unermtidliche Begleitung durch meine Arbeit und die anregenden Diskussionen,
...... In Figure 6 concentrations vs. temperature are presented for an empty.
Research Collection
Doctoral Thesis
Selective catalytic reduction of NOx by olefins Author(s): Radtke, Frank Publication Date: 1996 Permanent Link: https://doi.org/10.3929/ethz-a-001693105
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ETH Library
DissETHNr. 11792
Selective
Catalytic Reduction
of NOx
by Olefins
A dissertation submitted to the
SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH for the
degree of Doctor of Technical Sciences
presented by Frank Radtke
Dipl. Chem.-Ing. born
ETH
January 1,1966
citizen of Ennetmoos
accepted
on
(NW)
the recommendation of
Prof. Dr. A. Baiker, examiner Prof. Dr. K.
Hungerbuhler, co-examiner
1996
Meiner lieben Frau
Tochter
Barbara,
Stephanie
meiner
sowie meiner
lieben Familie
Danksagung
Allen voran, danke ich Prof. A. Baiker fur seine
personliche Betreuung
sowie die wissenschaftliche Unterstutzung meiner Arbeit. Besonders mochte ich mich fur die Hilfe bei der Abfassung der wissenschaftlichen Publikationen
bedanken. Im Weiteren
gebuhrt mein ausserordentlicher Dank Herrn Prof.
Hungerbuhler fur die Bereitschaft
Mein besonderer Dank
zur
gilt
K.
Ubernahme des Korreferats.
ausserdem Dr. R.A.
unermtidliche Begleitung durch meine Arbeit und die
Koppel
fur seine
anregenden Diskussionen,
die ich mit ihm fuhren durfte. Ebenso sehr mochte ich
Sergio Tagliaferri
danken, der fur mich die Software-Entwicklung fur die Anlagesteuerung ubemommen hat. Im Weiteren danke ich Frau J. den
Oberflachenuntersuchungen
am
Weigel fur Ihren Beitrag
zu
Paul Scherrer Institut. Der mechanischen
sowie der elektronischen Werkstatt unter der
Leitung von Herrn H. Seinecke
resp. Herrn M. Wohlwend danke ich fur ihre
praktische Unterstutzung beim
Aufbau der
Versuchsapparatur.
Fur die finanzielle
Unterstutzung gilt mein Dank dem "Schweizerischen
Bundesamt fur Umwelt, Wald und Landschaft" sowie dem "Nationalen
Energie-Forschungs-Fonds".
Schliesslich mochte ich all jenen
aus
der
Doktorandengruppe danken,
die
mich wahrend der letzten vier Jahre wahrend der Arbeit wie auch in der
Freizeit
begleitet haben.
Table of contents
Abstract
1
Zusammeofassung
3
Chapt.
INTRODUCTION
1
5
Automotive emission control standards
7
Diesel
8
engines
Emissions of Diesel engines Parameters
9
influencing the Diesel emissions
11
Scope of this thesis Chapt.
2
17
EXPERIMENTAL
Apparatus
21
Experimental procedures
33
Materials
45
Chapt. I. II. UJ.
Chapt.
3
BEHAVIOUR of Cu-ION EXCHANGED ZSM-5
Formation of Hydrogen
Effect of Water
on
Cyanide
....
the Formation of Byproducts
Formation of HNCO and other 4
and Nitrous Oxides
Byproducts
BEHAVIOUR of ALUMINA CATALYSTS
Chapt.5 BEHAVIOUR of COPPER/ALUMINA CATALYSTS
50
60 68
74
90
Final Remarks
133
List of Publications
135
Curriculum Vitae/ Lebenslauf
137
1
Abstract
The removal of nitrogen oxides from the exhaust of lean-burn
fuelled and diesel-foelled engines,
operating under net oxidizing conditions, has
recently attracted considerable attention. systems (A1203, Cu/Al203 and as
catalysts for
excess
harmful
Cu/ZSM-5)
work, three different catalytic
investigated for their suitability
are
Special emphasis is given
byproducts such
(NH3)
ammonia
In this
the selective reduction of nitrogen oxides
oxygen.
the formation of
to
(N20). The effect
potentially
of reaction temperature,
nitrogen oxide (NO, NOA. hydrocarbon (ethene, propene) and the formation of byproducts is
different atmospheres
by hydrocarbons in
hydrogen cyanide (HCN), cyanic acid (HNCO),
as
and nitrous oxide
temperature-programmed
gasoline
investigated.
surface reactions
used
were
to
and water
In situ FTTR
(TPSR)
investigate
activity
on
spectroscopy and
of adsorbed
the nature and
species in
reactivity
of
adsorbates formed under reaction conditions. The
catalytic activity was strongly influenced by the presence of water in
the feed. The effects of the other parameters
performance generally decreased, except when reduction of NOx were
over
were
propene
Cu/ZSM-5. Over Cu/ZSM-5
obtained, when ethene
was
used
as
was
reduced
impregnation performance. CuO),
the
maximum
of
For
more
y-Al203
efficiently
clearly higher conversion
In contrast, with
with copper led
to
an
was no
Y-A1203
extensive loss of this
dry feeds and with increasing CuO loading (0.46
of nitrogen
used for the
than NO with both reductants. The
catalysts reached maximum activity
yield
was
reducing agent, while there
significant difference when starting from NO or N02. N02
suppressed and the
slightly decreased.
at lower
to 1.65
wt%
temperature and the
2
As
regards the byproducts, their formation
type of catalyst, the
use
of either NO
or
N02, the
and the presence of water in the feed. With
tendency to form HCN
compared to
as
HCN formation. This contrasts the
production
was not
catalyst, HNCO
was
as
of the Cu For
reductant
loading,
as a
reductant
ethene showed
findings with Cu/ZSM-5,
a
lower
suppressed
where HCN
the presence of water. On this whereas
temperature range. NH3
same
the copper
over
y-A1203
additionally for dry feeds,
in the presence of water in the propene
alkene used
propene. Additon of water
significantly altered by found
strongly influenced by the
was
NH3 appeared
was
formed with
containing y-Al203 catalysts independent
the type of NOx and the presence of water.
dry feeds, precursor species for NH3 could be found on the surface for
both reductants. Reference TPSR measurements widi acetonitrile and
isocyanate showed the formation of NH3 in the similar
conditions
giving evidence
intermediates formed found in the
be detected
on
same
nitrile
mat
temperature range under as
well
catalyst surface could be the
the
ethyl
as
isocyanate
source
of ammonia
catalytic activity testing. Furthermore, N-containing species could
by
FTIR spectroscopy, when the
feed. Upon heating in H^^
predominantly isocyanate
cyanide
surface
sample
species
surface intermediates
was
were
appeared
loaded with
produced,
a
dry
whereas
in the spectra when
heating in Oj/Nj. The
findings are in accordance with a mechanism,
precursor, which
isocyanate a
pathway
and/or to
can
be
a
nitrile
or
an
oxime
cyanide species. Hydrolysis
ammonia.
Abstract
where
a
nitrogen containing
species,
reacts to
of these intermediates
surface
provides
3
Zusammenfassung
Der Entwicklung eines Verfahrens
zur
Entstickung der Abgase
von
Diesel- und
Magergemischmotoren wird weltweit besondere Bedeutung beigemessen. der
vorliegenden Arbeit wurden
(A1203, Cu/Al203
und
Katalysatorsysteme
Cu/ZSM-5) bezuglich ihres katalytischen Verhaltens in
der selektiven Reduktion Luftiiberschuss
drei unterschiedliche
In
von
Stickoxiden mit Kohlenwasserstoffen unter
(Alternativ-SCR)
untersucht. Von besonderem Interesse
war
dabei die Untersuchung der Bildung potentiell gefahrlicher Nebenprodukte wie Blausaure
(N20).
(HCN), Isocyansaure (HNCO), Ammoniak (NH3) und Lachgas
Der Einfluss der
Propen),
der
Reaktionstemperatur,
des Reduktionsmittels
Srickoxidkomponente (NO, N02),
sowie
von
(Ethen,
Wasser auf das
katalytische Verhalten und auf die Bildung der Nebenprodukte wurde untersucht. Die Art und Reaktivitat, der unter
Reaktionsbedingungen auf den
Katalysatoren gebildeten Oberflachenspezies wurde mittels
in situ FTIR-
Spektroskopie und Temperatur-programmierter Oberflachenreaktion (TPSR) in verschiedenen
Die
Gasatmospharen untersucht.
katalytische Aktivitat wird durch die Anwesenheit von Wasser stark
beeinflusst. So werden die Wirkungen anderer Parameter unterdruckt und die
katalytische Aktivitat nimmt, iiber Cu/ZSM-5
Die
wenn
ob NO oder
wird N02 mit
Propylen
zur
Reduktion
von
NOx
eingesetzt wird, generell ab. Mit Cu/ZSM-5 wurden deutlich
hohere Umsatze erzielt,
unabhangig
ausser wenn
N02
Ethylen als Reduktionsmittel verwendet wurde, das
Ausgangsprodukt
war.
Im
Gegensatz dazu
A1203 durch beide Reduktionsmittel effizienter reduziert
Impragnierung
von
A1203
mit
dieser Effizienz. In Abwesenheit
Kupfer fuhrt
von
zum
als NO.
weitgehenden Verlust
Wasser wird der maximale Umsatz mit
4
zunehmender
Beladung (0.46 bis
1.65
CuO) bereits bei tieferen
wt%
Temperaturen erreicht und nimmt dabei leicht ab. Bezogen auf die Nebenprodukte, wird deren Bildung durch die Wahl des
Katalysators resp. der Kupferbeladung, und durch die Anwesenheit
Ethylen, unabhangig von zur
HCN-Bildung,
unterdruckt sie
im
der
Katalysator wurde
Wasser stark beeinflusst. Mit
zu
Propylen,
Dies steht im
Wasser
nur
von
und die
resp.
Eduktgemischen
Vorlaufer des
Wasser im
Wasser
damit ist einen Hinweis
beladenen
hat. Diese in
bei s&mtlichen ob
man
dabei
Kupfervon
NO
war.
Messungen mit
vergleichbarer Weise NH3 gebildet und
kommen kann. FTIR
Katalysatoren, lassen die wenn
TPSR Referenz
gegeben, dass eine dieser Spezies als Vorlaufer fur die
NH3 in Frage
spezies erkennen,
gefunden,
NH3 konnten auf der Katalysatoroberflache, bei trockenem
Acetonitril und Ethyhsocyanat wurde in
von
Wasser
gleichen Temperaturbereich NH3
beigemischt
Eduktgas, nachgewiesen werden. Bei
Bildung
von
auch HNCO
A1203 Katalysatoren gefunden, unabhangig,
N02 ausging oder ob
Zugabe
Gegensatz zum Cu/ZSM-5, dessen
nachgewiesen werden konnte. NH3 wurde mit Propylen beladenen
A1203 zeigt
unwesentlich beeinflusst wird. Bei diesem
bei trockenen
wahrend in Anwesenheit
Stickoxids, des Reduktionsmittels
Kupferbeladung, eine markant niedrigere Tendenz
Vergleich
vollstandig.
HCN-Bildung durch
von
des
Anwesenheit
Messungen, ausgehend von
die Beladung in wasserfreier
von
N-haltigen Oberflachen-
Atmosphare stattgefunden
reagieren zu oberflachengebundenen Cyanidspezies, bei Aufheizen
H.^2, wahrend,
in
0^2, tiberwiegend Isocyanatspezdes entstehen.
Resultate stehen in Eintracht mit einem
Diese
Mechanismus, bei dem eine N-haltige
Oberflachenspezie (ein Oxim oder eine Nitrilspezie) weiter
zu
Oberflachen-
Isocyanat und/oder -Nitril reagiert. Die Hydrolyse dieser Zwischenprodukte stellen einen
Reaktionsweg zu Ammoniak
dar.
Zusammenfassung
5
Chapter
1
Introduction
Global reservoirs like the atmosphere and the lakes and rivers)
local and
are
aquatic system (oceans,
linked to each other and thus support by transportation the
global distribution of solid, liquid and
disaster of the nuclear power station at
gaseous emissions. With the
Tschernobyl (Ukraine) in 1986, large
amounts of radioactive dust has been distributed all
within
atmosphere. Furthermore
the
year showed the
conflagration
at
Schweizerhalle
the
same
the
transportation capability of aquatic systems, like Besides
gases'
or
can occur
the
especially
sun
areas
the
as
'greenhouse
due to reactions of NOx and
light.
greenhouse
gases, not all of them result from human most
abundant of them
(carbon dioxide)
major part from combustion processes of fossil fuels,
like the
next to natural
activity of volcanos. Further greenhouse gases are nitrous oxide
(major source for this molecule
in the
atmosphere
is of microbiological
origin)
[1] and methane, the most powerful of them [2]. With their accumulation atmosphere,
a
of
the Rhine.
in the atmosphere, such
activities, but the emissions of the
sources
(Switzerland) in
accumulation and transformation
processes,
the formation of ozone in urban
Concerning
a
and Asia
regionally limited, but not less important, effects
transportation
hydrocarbons initiated by
result to
Europe
days, showing the tremendous transportation capability of the
some
processes
over
temperature increase has
to be
Introduction
expected
due to
a more
in the
efficient
6
absorption of the
energy
increase of the
atmosphere
sun
on
light. The
consequences of this temperature
global weather conditions
are
actually discussed
by experts.
Examples
for the transformation processes
smog, acid rain and
ozone
oxidation reactions from
are
the formation of summer
in urban areas, with the latter
formed
being
photochemically active substances like nitrogen
by
oxides
e.g. OH radicals.
NO„ originates mainly from
combustion processes, but also from biomass
burning and hghtnings [3],
(NOJ
and
hydrocarbons with
whereas the main
sources
evaporative emissions
for
and
hydrocarbons
unburned tail
pipe emissions,
refuelling losses [4].
Finally nitrogen dioxide
is known to
alterations of the immune system matters
are
cause
bronchitis, pneumonia and
[5], while solid emissions like particulate
(PM), resulting from Diesel engines are suspected to have carcinogenic
properties, due to the polynuclear aromatic hydrocarbons (PAH), the
adsorbed
on
particles [6]. The effects of the
transportation, accumulation
and transformation
processes of emissions
resulting from combustion of fossil fuels have forced
several governments to
legislate emission standards
In the
EEC and
following sections the standards
of the
for
pollutants.
legislative
in the U.S.A., the
Japan are discussed. The formation processes of particulates [6] and
nitric oxides
[3, 5] resulting from
the
use
of Diesel
engines
as
well
as
the
parameters influencing the exhaust gas composition will be introduced and the
chapter will
end with the scope of this thesis.
Chapter
1
7
Automotive emission control standards
The U.S.A. started
already in
1955 to set up limits for the emissions of
HC, CO and NOx for passenger cars followed by the Air Quality Act of 1967, and the Clean Air Act Amendments of 1970 and 1977. In the 90* refined and
strengthened pollution
control
was
Clean Air Act Amendments. It is divided into from which Title II treats mobile
sources
[7].
vehicles of the U.S. and California Standards
a
a
further
established with the
recent
total often sections
The actual limits for are
presented in
(Titles)
light-duty
Table 1.
TABLE 1 U S and California Emission Standards
Year and standard
Pollutant
Hydrocarbons
Carbon monoxide
Nitrogen oxides
1990 U.S.
0 41
34
10
1994 U.S.
0 25
34
0 40
0 25
34
0 40
1993 California 1994
(TLEV)1
0125
34
0 40
(LEV)*
0 075
34
0 20
0 040
17
0 20
1997
1997
[g/milej
-
2003
(ULEV)3
1
TLEV= transitional low
2
LEV Low
3
ULEV Ultra low
emission
vehicle
vehicle
emission
In Western
legislated in
emission
vehicle
Europe first limitations of automotive emissions
1987 with the
so
emissions for heavy-duty vehicles
were
called FAV2 standard. In this standard the as a
major part
Introduction
of the diesel fuelled vehicles
g
are
limited: CO
g/kWh).
(8.4 g/kWh), HC (2.1 g/kWh), NOx (14.4 g/kWh)
In 1992 the EURO I standard became actual CO, HC & NO, PM 0.14
(2.72, 0.97,
g/km) [8]
and since 1996 the
new
EURO II standard is
introduced, limiting the emissions of CO, HC, NOx and PM 0.15
and PM 0.7
to
4, 1.1,7 and
g/kWh, respectively [9]. New Standards (EURO IH) are now in discussion
to lower the
NOx limit
g/kWh.
to at least 5.0
Japan's emission control standards are more or less equivalent to the U.S. standard. TABLE 2
Operation parameters
of Diesel
engines
versus
Otto
Otto
engine
Diesel
engines
engine
Internal combustion
Internal combustion
Combustion type
Cyclic
Cyclic
Air/Fuel Mixing
Heterogenous
Homogenous
Auto
External
Process type
Ignition Type 30
Operation pressure Temperature X-
at
compression
0
X
Diesel
Oxygen
0.8
Gaseous
components
FuelC/H/O/S/N
=0 amount
composition
=&
=&
composition
\*
Engine load, speed and displacement Engine wear and comsumption
Particulates
lube oil
=& amount =0
composition
=S> size
distribution
Engine fuel consumption
Lube oil additives
4 1
Figure
2:
Exhaust gas aftertreatment devices
Parameters that influence the tail
pipe powered engine [6] H PAH: Polyaromatic hydrocarbon 2)
found to
Sampling and analytical methods
Test cycle
Fuel additives
A
emissions of a diesel
T95: temperature at which 95% of a fuel has been distilled. Chapter I
13
number of nozzle The
(EPEFE)
openings and
European Programme
a
on
Emissions, Fuels and Engine Technologies
up from 1993 to 1995 to
was set
technical connections in relation
emission of
moderate swirl ratio.
gasoline
to
and diesel
fuel
provide relevant data
quahty
and
sets and
engine technology for the
powered engines. This
programm
was
supported by the European automobile industries, European mineral oil companies
as
well
by
as
the EC-Commission
(EEC).
The influence of the
engine technology was a minor part of the programm but was in general found to
have
fuel
bigger affects
on
the emissions than the influences found with
qualities [16]. Similar results
were
obtained from
Copper
varying
et al. who
compared the emissions of two different types of diesel powered engines [17]. Fuel properties
In
a
study from 1990
cooperation with the
investigated
the
oil
the Swedish Environmental Protection
industry and
composition
fuels lead to more
terms of emissions
further shown that the
sulphur content
the gaseous emissions but
the
that
use
of
an
high
heavy duty
ignition improver
may be
neglected with regard
The influence of fuel
fuel parameters: density, PAH content,
heavy duty vehicles.
It
density fuels It
are
was
marked influence
composition
also part of the EPEFE programm mentioned above.
total of 11 different fuels
vehicles
compared to high density fuels. no
[18],
aromatic contents in
and that low
of the fuel has
in
on
significantly affected particulate and SOx emissions.
composition of the emissions. was
study revealed
high levels of PAH in the emissions
favourable in
Finally
motor vehicle manufacturers
of exhaust emissions bom
with different diesel fuels. The
Agency,
was
was
cetane
blended and
on
to the
emissions
By varying the four
number and T95 temperature
compared, using
8
fight duty and
a
5
observed that the reduction of the density, the PAH
Introduction
14
content and the T95
temperature and
the
of
NOx emissions
an
increase of the cetane number reduces
heavy duty vehicles. The
necessary to reduce the
particulate emissions
cetane number is needed.
Concerning die reduction
heavy duty vehicles,
a
fuel
same
specifications
of passenger
cars
but
lower
of particulate emissions for
low PAH content is necessary, while with
lower NOx emissions of passenger cars,
a
are
additionally a higher
regard
to
T95 temperature
is necessary. The formations of NOx and
other, leading either emissions
as
particulates
are
to low concentrations of
presented in Figure
always
NOx
or
correlated to each to low
particulate
3.
study as baseline for the EPEFE programm disclosed already
A literature
known correlations between the emission and fuel parameters such influence of the
sulphur content
100 ppm elimination of the
and the type of additives in the fuel
sulphur
content in
a
fuel,
a
as
the
[16].
Per
reduction of the
particulate emission of 0.16 wt% for passenger cars and 0.87 wt% for heavy
duty vehicles improvers
can
e.g.
%v/v) [19])
be achieved. Fuel additives
isopropyl nitrate (25 %v/v)
have
an
influence
on
or
(like detergents
and
ignition
triethylene glycol dinitrate (4
the cleanness of the
engine and injection
system. Over the lifetime of an engine they may affect the emission and power values. It is obvious that the emissions vary with the age of the
abrasion processes of the
injection system, the fittings and bearings.
the lifetime of these parts
level, the shown
use
of non
by Paesler [20].
diesel fuel. Due
to
as
well
aggressive
elimination processes
on
the
engine due
as
to maintain the
To
to
prolong
initially lower emission
and abrasive lubricants is evident
as
He described the consequence of the
could be
sulphur
the content of natural surface active components in
desulphuration
process
Chapter
I
a
a
decrease of these abrasion
15
reducing of the to
substances had to be
accepted, leading to
injection system. So it was necessary
to
especially
shorter hfetime
develop
new
groups of additives
maintain the lubrication effect of the diesel fuel. When using new cleaner diesel fuels and
composition of emissions can be to
a
the
the
additives, faster changes ofthe
obtained to all vehicles at the
rapid replacement of diesel fuels by refilling.
With
new
same
time, due
developments
engine manufacturer side, however, the bigger improvements
achieved with
interest
methyl
are
ester
new
use
[6], Liquified Petroleum Gas (LPG) could
(CNG) [21]. Promising results
of alcohols or
[19], Rapeseed
Compressed Natural
already be obtained with
an
g/kWh)
Gas
LPG fuelled
designed by Dutch DAF Company [21]. The exhaust emission
reached much lower values than denned in the EURO II standards NO
compared to
be
engine technologies. Other technologies of increasing
alternative fuel concepts like the
passenger bus
can
on
7.0
and PM
g/kWh), (0.05
i
CO
to 0.15
k
TC
(1.0 compared
to 4.0
g/kWh),
g/kWh).
engines
NA
engines
CO CO
1 1
1 NOx Figure
3:
concentration particulate and NO, engine designs [19]. Normally aspirated
Correlation between
emissions for different NA:
TC: Turbocharged
Introduction
HC
(0.6
(1.0
to 1.1
16
Catalytic
after treatment
For
stationary systems suitable applications
have been
engines due
as
to the relative
due to the
reducing agent,
the
injection system of the Other clean-up
CaO
or
technology
is not suitable for mobile diesel
costly support of the aftercleaning system and
high toxicity of ammonia. By replacing ammonia with problem of the toxicity could be reduced due
formation of ammonia, but
of NO to
cleaning devices
successfully introduced with the selective catalytic reduction of NOx
with ammonia. However, this
moreover
of flue gas
making additional equipment
water
dissolved
techniques
such
to in situ
necessary for the
reducing agent.
as
N02, followed by absorption
urea
wet
systems like gas phase oxidation
in
solution containing NaOH, NH3,
a
CaO/CaCOj, or dry systems like non selective catalytic (NSCR)
catalytic reduction techniques (NCR) [3]
are
also
or non
available, but proved
to be
less efficient. A
in
completely new challenge for the selective catalytic reduction of NOx
excess
who
of oxygen
were
the
findings
of Iwamoto
[22] and Held
et al.
[23],
independently reported hydrocarbons to be a selective reducing agent
copper
containing
zeolites such
as
Cu/ZSM-5. With their
hydrocarbons could not be handled any more agents [24]. As of alternative
a
as non
selective
result, increased attention has been given
findings
over
the
catalytic reducing
to the
development
catalyst systems. Different types of zeolites with and without ion
exchanged cations [25,26,27,28] without transition metal additives reduce NOx with
hydrocarbons
as
well
as
various metal oxides with and
[28,29,30,31] have been shown
in the presence of oxygen. However,
velocity performance, selectivity behaviour and durability the presence of steam and
to
sulphur
oxides have to be
Chapter
1
of these
selectively high
space
catalysts in
improved
to make
17
application feasible.
Scope
of this thesis
The
objective of the present work was to investigate
three different catalyst systems,
Cu/ZSM-5,
for the selective
v-Al203,
copper
catalytic reduction
presence of excess oxygen and to
investigate
the
suitability
of
impregnated A1203 and
of
N0X by olefins in the
possible formation of harmful
the
byproducts such as hydrogen cyanide, cyanic acid,
ammonia and nitrous oxide
in the
devoted to the effects of the
course
of tiie reaction.
kind of nitrogen oxide (NO as a
reducing agent,
Special emphasis
or
was
NOj), the hydrocarbon (CjH4
and of water
on
the overall
or
C3IL,) employed
catalytic performance and
on
the formation of byproducts. For this purpose
equipped
with
a
a
specific experimental setup
gas cell for gas
analysis
was
with
FT-IR spectrometer
a
set up, which allowed the
simultaneous detection of IR-active components in the gas
computer controlled apparatus consisted essentially of continuous tubular fixed-bed microreactor and In order to to
gas
gas
The
fully
mixing unit,
on
the nature and
were
and
reactivity of surface species formed
under reaction conditions, in situ FTIR and
(TPSR) experiments
a
analysis system.
gain insight into the mechanism of the byproduct formation
obtain information
reaction
me
a
phase.
temperature-programmed surface
performed
CuO/Al203 catalyst.
Introduction
in different
atmospheres
on
the
IS
References
[1 ]
D.R. Bates and P.B.
Hays Atmospheric
nitrous
oxide, Planet. Space Sci.
15(1967), 189 [2]
Oh,
S.H.
P.J. Mitchell and R M. Siewert ACS
Symp.
Series
(ed's.
R.G.
Silver, JE. Sawyer and J.C Summers) 495 (1991) Chapt 2.
[3]
H. Bosch and F. Janssen Catal.
[4]
J.C. Summers and R.G. Silver ACS Symp. Series (ed's. R. G. Silver, J.E.
Sawyer and J.C. Summers)
495
[5]
J.N. Armor Appl. Catal. B 1
[6]
E.S. Lox, B.H.
Engler
Today 2 (1988) 369.
(1991) Chapt
1
221.
(1992)
and E. Koberstein Diesel Emission Control,
Catalysis and Automotive
Pollution Control II, Elsevier Sci.
(ed. A.
Crucq) (1991) 291.
[7]
J.C. Summers, J.E.
Sawyer and R G.
Silver ACS Symp. Series
(ed's.
R. G.
Silver, J.E. Sawyer and J.C. Summers) 495 (1991) Chapt 8.
[8]
T.J.
Truex, R.A. Searles and D.C. Sun Plat. Met. Rev. 36(1) (1992) 2.
[9]
B.
Ursprung "Oekologische Aspekte",
Shell
Dieseltagung Lucerne (Switzerland) February [10]
G.W. Smith SAEpaper 820466
[11]
J. Zeldovich Oxidation
[12] C.P.
(1996).
(1982)
ofnitrogen
Rend. Acad. Sci. USSR 51
6
(Switzerland), Shell
in
combustion and
explosion, Compt.
(1946).
Fenimore Formation of nitric oxide from fuel nitrogen
flames, Combust. Flame 19 (1972) 289.
Chapter
I
in
ethylene
19
[13]
C.P. Fenimore Formation
flames, 13th Int. Symp.
on
of nitric oxide
in
premixed hydrocarbon
Combustion, (1970) The combustion Institute,
Pittsburgh (1971)373.
[14]
A. Gill SAE paper 880350
[15]
T.
Murayama,
861232
[16]
M.
N.
(1988).
Miyamoto,
T. Chikahisa and K. Ysmsae SAE Paper
(1986).
Signer "Erkenntnisse
(EPEFE)",
Iveco
aus
dem
Europaischen
Motorenforschung AG,
Shell
Auto-oil
Programm
Dieseltagung
Lucerne
(Switzerland) February 6,1996
[17]
B.J.
[18]
K.E.
Copper and S.A. RorhP/or.
J.M. Betton automotive
[20]
H. Paesler
industry (ed.
178.
R. Westerholm Swedish
Agency Report Series, Stockholm (1990).
"Replacement of diesel by alcohol", J.A.G.
Drake) Roy.
Soc.
Chemicals
for the
of Chemistry (1991).
"Emfluss moderner Additivtechnologie auf das Leistungs-
Emissionsverhalten
von
und
heutigen Dieselkraftstqffen", Deutsche Shell AG
PAE Labor, Shell Dieseltagung Lucerne
[21] M.
35(4) (1991)
Egeback, G. Mason, U. Rannug and
Environmental Protection
[19]
Met. Rev.
(Switzerland) February 6,1996.
"Emfuhrung Fliissiggasmotor LT
de Vries and P. Schoenenmakers
160 LPG", DAF Components, Shell Dieseltagung Lucerne
(Switzerland)
February 6,1996.
[22]
M. Iwamoto, NMizuno and H Yahiro
Workshop m Catalytic Science
and
m
Technologyfor Alternative Energy
and Global Environmental Protection
[23] W.Held,
A
Konig
and L.
Proceedings of First Japan-EC
Tokyo December 2-4, (1991)
Puppe SAE paper 900496 (1990) Introduction
20
[24]
Anderson, W.J. Green and D.R. Steele Ind. Eng. Chem.
H.C.
53
(1961)
199.
[25]
C.J.
Bennet, P.S. Bennet, S.E. Golunski, J.W. Hayes and A.P. Walker
Appl. Catal. 86(A) (1992)LI. [26] C.N. Montreuil andM. Shelef Appl. Catal. 1(B) (1992) LI.
[27]
Y. Li and J. Armor Appl. Catal.
[28]
M.
1(B) (1992) LI.
Sasaki, H. Hamada, Y. Kintaichi and T. Ito Catal. Lett. 15 (1992) 297.
[29] Y.Ukisu,
S.
Sato, G. Muramatsu and K. Yoshida Catal. Lett. 11 (1991)
177.
[30]
S. Subramanian, R.J. Res.
[31]
A.
Kudla,
W. Chun and S. Chattha Ind.
Eng.
Chem.
32(1993)1805.
Obuchi,
Appl.
A.
Catal.
Ohi,
M.
Nakamura, A. Ogata, K. Mizuno and H. Obuchi
2(B) (1993) 71.
Chapter
I
21
Chapter
2
Experimental
Apparatus
General For
screening experiments,
an
apparatus
was
built, allowing the
investigation ofthree catalysts
at the same time and the control
concentrations
a
components
by
means
mixed
were
of
could be
water
splitting system.
by means of mass
could be additionally fed with
components, the
flow
a
A total of 8 gas
flow controllers
microstep pump.
of the inlet gas
(mfc)
phase
and water
The flow of all gas
phase
feeding, the furnace temperatures and the valve settings
changed either manually
or
by
remote control via
a
computer. As
analytical system a Fourier Transform Infrared (FTIR) spectrometer equipped with
a
heatable gas cell
The spectrometer means
of a
used for gas
phase analysis
required a second computer, which
shown in
as
was
used
Figure
1.
slave
by
as a
TTL-signal. This computer together with a macro programm (OPUS
2.0) served for the The
was
control and data
acquisition of the
gas
phase analysis.
following paragraphs briefly specify the components of the system,
which essentially consisted of
composition,
a
gas
dosing system, the analysis of gas
the temperature and system control.
Experimental
22 HC
:©
Figure
1:
Flow sheet of the
N2
NO
so2
co2
:© :©
experimental setup
Chapter
2
CO
ic)
h2o
(fic)
23
Gas
dosing system
The gas
mixing manifold
desired feed gas
controllers
compositions,
(Brooks 5850E).
was
as
stream contained die
balance gas
stream at room
in Table
was
at 393
nitrogen,
chosen
as
of NO, oxygen
temperature by
K), a
containing the
NO in
of mass flow
or
shown in
mixture and
NOx component. For
gas mixtures
fed into the 4.9% NO in
three-way
valve. The
nitrogen
high partial
together with a residence time of ca. was
detected for Feeds 3 and
conversion of NO to
S02
were
hydrocarbon/nitrogen
of a
means
(Table 1), indicating that the CO, C02, H2
means
1. The main
as
7 min facilitated the formation of N02. No NO
gases like
1, by
Figure
was
pressure of oxygen and nitrogen monoxide
4
the concentrations of the
Two streams of independently blended gases
(thermostated
containing N02 in place
adjust
to
specified
mixed in the hot box
pure oxygen, when NO
used
could be fed
N02
was
100%. Other
optionally into the
stream
nitrogen mixture.
TABLE 1
Simulated exhaust
compositions (feed gas mixtures) employed in catalytic studies; balance
NO
NO,
C,H4
CjH,
O,
H,0
[ppm|
[ppm]
[ppm]
[ppm]
[%]
[%]
1/lw
980/(940)
0
0
910/(860)
2.0/(2.0)
0/(10)
2/2w
970/(940)
0
1390/(1260)
0
2.0/(2.0)
0/(10)
3/3w
0
970/(940)
0
910/(860)
1.9/(2.0)
0/(10)
4/4w
0
980/(950)
1450/(1270)
0
1.9/(2.0)
0/(10)
Feed*
•
nitrogen.
Values in
with
parenthesis correspond to
feeds
containing
w.
Experimental
10% water, which
are
denoted
24
After
a
of 8
mixing section
tube
m
length,
the gas flow
was
equal flows using silica capillaries (length 500 mm, i.d. 0.32 mm). pressure of 9.5 bar
2.4
l(STP)/min. flows
splitted
was
The
was
used for all components to
resulting
used to
ensure a
gas flow rates varied within
measure
the feed
mm), which could be operated
6
effluent
was
An
into 4
operation
total flow rate of
±
5%. One of the
concentration, whereas the other
flows could be directed independently to the three U-tube quartz
(i.d. of
split
in series
glass
The reactor
parallel.
or
reactors
either directed to the gas cell of the FTIR spectrometer
or
to
the
purge.
Analysis
of gas
composition
The Fourier Transform Infrared (FTIR) spectrometer for gas a
analysis
at the reactor
heatable gas cell (3.2
m
inlet and outlet,
path length, gold
100 ml volume; Infrared
respectively,
as
shadowed
Analysis Inc.) and
areas
in
Figure
was
a
MCT detector. To avoid
tubing were heated
phase components,
developed according to the information given by Bruker [1]. adapted
the present system and
to
equipped with
at 393
K,
1.
For calibration of the relevant gas
were
used
coated mirrors, ZnSe windows and
condensation in the system, the gas cell and all indicated
(Bruker IFS 66)
are
a
method
was
Basic parameters
presented in Table
2.
Influence of resolution
High resolution scanning was chosen to obtain maximum separation of the
absorption
bands of the individual
limit of calibrated and, In
Figure 2
as a
compounds
and to increase the detection
further positive aspect, of uncalibrated components.
absorbance spectra of carbon monoxide
recorded with
a
resolution of A
=
0.5, B
=
Chapter
2
are
1.0 and C
=
presented, which 2.0
were
cm"1, respectively.
25
TABLE 2 Basic parameters of FTIR-spectrometers used for the
Apparative parameters
Steady
state and
experiments
TPSR
experiments
DRIFT experiments
(Bruk er, IFS 55)
(Bruker, IFS 66) optical parameters
Globar(MIR)
Globar(\OR)
KBr
KBr
MCT
MCT
Mertz
Mertz
Blackmann-Harris 4
Blackmann-Harris 3
Term
Term
4
2
cm"1
4 cm-'
50
256
absorbance
reflectance
source
beam
splitter
detector
FT parameters
phase
correction
apodization
zero
function
filling factor
resolution
setup experiment
0 5
scans
result spectrum
Influence of pressure
The gas cell
heated box
was
connected to the purge via
(see Figure 1)
to
MS. In die purge line the gas This closed system
over
increasing flow rate
allow further gas phase was
concentrations.
analysis, for example by
an
increase of the cell pressure with
of the feed. The pressure in the cell
correlation influenced the were
separate exit from the
remixed with the effluent gas of the reactors.
the gas cell led to
about 38 mbar when the flow rate
spectra
a
was
raised from 0
quantification of gas
recorded at
a
Consequently
thereby increased by
to 575
ml(STP)/min. This
mixtures when the calibration
different flow rate, resulting in inaccurate
the calibration spectra
Experimental
were
corrected
by linear
26
2300
2250
2200
Wavenumber Figure
2:
2100
2150
FTIR spectra of carbon monoxide
(all
2050
2000
-1 /cm
50
scans) recorded with different
resolutions: A resolution 0.5 cm-' B
resolution 1.0cm'
C resolution 2.0 cm-1
correlation of the pressure and the calibration offset. The influence of the gas cell pressure
illustrated, when analysing different flow rates.
while in the second
external exit of the hotbox to die purge 3. With
the
quantification
e.g. I'OOO ppm carbon monoxide in
During the first run the cell
atmosphere (symbol: E)
Figure
on
was
run
connected
it
(symbol: ).
was
can
nitrogen
directly
be at
to the
connected via the
The results
are
shown in
decreasing flow rate, the difference between the two calculated
values diminishes. As emerges from decrease
Figure 3, the measured concentration
markedly with decreasing flow rate. This
of CO still
influence of the flow rate
on
the concentration measurements could be attributed to the behaviour of the mass
flow controllers
(mfc), when working Chapter 2
at
low setpoints.
Readjusting the
27
linearity of all mfc's resulted in a standard CO), when changing the rate over the (symbol: A)
compared
as
(for I'OOO
whole range from 0 to 575
ppm
ml(STP)/min
to 122 ppm without this correction.
200
Gas Figure 3:
deviation of 28 ppm
Influence of pressure
400
300
500
600
flew/rri(STP)*rrirf1 on
the
quantification of I'OOO ppm
CO in
nitrogen
at
different flow rates:
calculation without pressure correction of the calibration spectra; sd
-
141
ppm D
122 ppm calculation for the gas cell open to the atmosphere; sd 28 ppm calculation after pressure correction and mfc readjustment; sd =
=
Calibration ranges
For per
cahbration, absorbance FTIR spectra (resolution 0.5 cm'1, 50
spectrum)
concentrations
of
specially prepared
were
cahbration gas mixtures with known
recorded for each component.
background spectra.
scans
The cahbration for
C02
Experimental
Nitrogen was used for die
and
H20
was
carried out
by
28
oxidizing corresponding concentrations of propene and ethene (2nd series) 866 K
over
1 wt%
4.9% nitric oxide in was
Pd/Al203. Nitrogen dioxide nitrogen with
was
calibrated
oxygen. In these calibration
found, indicating that the conversion
to
N02
was
at
by premixing
spectra,
no
NO
100%.
TABLE 3
Calibrated components with the number of calibration spectra, the range, the
integration method
number
component
of spectra
34
Nitrogen monoxide
Nitrogen dioxide
(24)
33
integrated spectral
and the calibrated concentration range
integrated spectral
[cm']
range
integration
calibrated
method
concentration
[ppm]
(cubic)
range
1872 14 -1877 20
area
24
-
1752
1612 00-1613 75
area
24
-
1947
Nitrous oxide
12
2213 9-2214 0
peak height
5-198
Ammonia
12
1082 7 -1087 9
area
5-100
Hydrogen cyanide
9
712 3-712 7
peak height
5-101
Propene
35
2947
-
2957
area
24 -1947
Ethene
35
2984
-
2992
area
24-2920
Carbon monoxide
39
(36)
2118-2133
area
24
Carbon dioxide
34
(40)
2294 8-2296 7
area
73-5840
Water
34
(40)
area
73
value
in
parenthesis correspond to
a
1987
-
second calibration
Concentrations of each component
absorption bands.
1994
-
2434
5840
series
were
obtained
by integrating specific
In Table 3 the number of cahbration spectra, the
and cahbration ranges for the components and the Chapter 2
-
integration
integration method
are
listed
29
An
appropriate software package (OPUS
vs.
2.0; Bruker) was used
to calculate
the concentrations of the feed and effluent gases. The accuracy in the
by
concentration measurements
FTIR
nitrogen dioxide, carbon dioxide
5% for all components except
was ±
(± 10%),
and water
as
evidenced
by
measurements with calibration gas mixtures.
The concentration of nitrogen formed by reduction of NOx
by using a mass balance
all
over
was
calculated,
nitrogen containing species (NO, N02, N20,
NH3 and HCN) (equation 2). S
i
=
*
The indices in and
NOj,
summarized
t^l^-products]
'
(1)
[(NOX- (NOx)J
out
stay for inlet and outlet concentrations of NO and
NO„ and 2 N-products represents all nitrogen containing
as
products, except N2. When
using
ethene
as
reducing agent, overlapping of the absorption
bands of ethene and nitric oxide occurred (1880 -1860 was
taken into account
using the relation given in
cm"1). This interference
eq. 2.
Reactor A
quartz glass U-tube
for the
defined
catalytic
tests.
position.
reactor with
inner diameter of 6
an
Quartz wool plugs
were
The temperature of the
thermocouple (Type K), located distribution over the catalyst bed
at
position
was
to fix the
catalyst
2. A
corrfirmed
Experimental
used
was
used
mm was
catalyst
recorded
in
by
a
a
nearly uniform temperature
by recording the temperature
30
at three
different
measurement, the on
positions
of the reactor
reactor was
reactor line 3. The
to 873 K while 150
(Figure 4).
For this temperature
filled with 250 mg of CuO/Al203 and mounted
temperature
was
increased in steps of 50 K from 473 K
ml(STP)/rnin nitrogen was passed
over
the
catalyst.
•8
Figure
4:
Positions of thermocouples (1-3) for the measurement over the catalyst
temperature bed.
Temperature and system The furnace controller allowed the control
parallel
control
(JUMO
DICON
Z), mounted in the control box,
control of four furnaces. The
could be changed manually
or
setpoints for temperature
electronically.
temperature control, the parameters of the controller furnaces
as
shown in Table 4. The
were
thermocouples (Type K), Chapter
2
For
an
optimal
adjusted for all for
recording
the
31
temperatures, with
were
in
a
increasing temperature
setpoint and
me
locations of me K
placed
were
separate tube inside die furnaces. Generally,
an
increasing deviation
catalyst temperature
thermocouples,
recorded for the
e.g. at
a
was
between the furnace
observed,
due to the different
setpoint temperature of 873 K only 860
catalyst bed.
TABLE 4
Standard
setpoints for the
furnaces of the
Xd=30
switching difference
Xp=ll
proportional
Tv=
25
apparatus
range for heating
retarding time
sec
T„= 90 sec
adjustment time
Cyl= 3
maximal
sec
switching frequency of the heatmg contact
limit of the positive output signal
Y,= 25%
W,= 273 K
lower set point limit
W.= 1373 K
upper set point limit
X„,X,= 0K
correction
of the actual value
The temperature programmed experiments demanded
Therefore the limit of the positive output time
(every
setpoints
200
that
seconds).
were
reactor
Table 5 lists the relevant
slightly different
linearity of the heating
signal (Y,)
a
linear heating rate.
had to be
changes
adapted
for the furnace
for each furnace. The standard deviation
rate was 4.7
K, 3 3 K and 5
6
K, respectively, for
line 1,2 and 3.
A master computer was used to control the remote
settings of the valves,
the furnace temperature, the flow rates of the different components TTL
with
signal, die
slave computer for
recording
Experimental
uie
and, via
a
FITR spectra. A software
32
package (written in
our
group) [2] allowed timed programming
of a series of
setpoints.
TABLE 5
Parameter set of Yt
(limit
of positive output
signal) for each fiimace during temperature
programmed surface reaction (adapted eveiy 200 seconds).
ointN"
reactor lines
Y, for line
1
Y,
for line 2
Y,
for line 3
1
11
14
12
2
12
14
12
3
13
16
14
4
14
16
14
5
15
17
16
6
16
17
16
7
17
19
18
8
18
20
18
9
19
22
20
10
20
24
20
11
21
24
22
12
22
27
22
13
23
27
24
14
24
29
24
15
25
29
26
Chapter
2
33
Experimental procedures
experiments
Basic
Apparative characteristics The flow rate a
knowledge of the purge behaviour of the gas was
cell in
necessary to determine the necessary purge time before
measurement. When
starting to early, the system
was
and no conclusive spectrum could be recorded, whereas to unnecessary
For
elucidating the optimal time, die
10
15
Concentration of NO mixture
•
o
a
transient state
starting to late have led
gas flow of
was
purged with
in
a
time /seconds
dependence of the purge
ml(STP)/min ml(STP)/min 1 150 ml(STP)/mm 2
in
nitrogen
series
series
Experimental
tune
of the gas cell for
3.5
pressure
25
20
containing I'OOO ppm NO
gas flow of 450 gas flow of 150
gas cell
I'OOO ppm nitric oxide in nitrogen passed
Purge 5:
still in
starting
prolongation of experiments.
l(STP)/min nitrogen, while
Figure
dependence of the
a
gas
34
relief valve
placed
in front of a three way valve. After
recording
spectra (resolution 0.5 cm'1,50 scans) the three way valve NO in
mixture. With this setup
nitrogen
was
a
background
switched to the
approximate step
an
response
experiment could be conducted. In
Figure
5 the results for two different flow rates
ml(STP)/min less than concentration. At reach
to
a
a
flow rate of 150
a
two
time with the runs
were
shown. With 450
necessary to reach
50 seconds
ml(STP)/min,
a
steady
were
state
necessary
constant concentration of NO. Due to memory limitation of die data
acquisition processor at
40 seconds
are
with
a
of the FTIR
only
10 spectra (20
scans) could be recorded
rapid scan TRS technique of the software package.
flow of 150 ml/min
range and achieve
were
necessary to record
Therefore
whole
me
purging
desired resolution of 12 spectra per minute. Run two
a
started 12 seconds after
was
switching the valve.
Chemical characteristics
Figure
In reactor an
6 concentrations
and for
(Figure 6A)
inlet feed gas
one
vs.
temperature
no
composition similar
reaction took place in boui
conversion and
became
N02 decomposition
significant
at
presented for
filled with 40 mg quartz wool to
experiments. to NO and
at
was
150
In die empty reactor ethene
02 started around
800 K and
quarz wool filled
slightly higher temperatures. This behaviour is
attributed to the role of quarz wool
as
radical trap
(3)
of the
homogenous
reactions. Note that NOx conversion remained below 10 %, whereas ethene conversion took
empty
from 465 to 1048 K. Below
higher temperatures, whereas in the
reactor, reactions started
an
(Figure 6B) for
Feed 4. The flow rate
nn(STP)/min and the temperature was increased 750 K
are
place.
Chapter
2
complete
35
500
600
700
900
800
1000 1100
Temperature /K Figure
6:
Concentrations of ethene(T), NOx(D),
N02(o) and
NO(a) in dependence of the temperature; 150 ml(STP)/min, Feed 4 (Table 1): A
empty U-tube
B
40 mg quartz wool in U-tube reactor
Flow rate
reactor
When only N02 in N2 was fed to the empty and quarz wool filled U-tube reactors, a
respectively a similar behaviour could
temperature of 800 K
experiments.
no
conversion of
Above this temperature,
pronounced in the empty
be observed
N02
to NO
(Figure 7). Up to
occurred for both
N02 conversion started, being
reactor as shown in
Figure
suppressed the homogenous decomposition of N02 to Experimental
7.
Quarz
NO and
wool
more
again
02. The stability
36
of the system at
873 K when
high temperatures
using quarz wool to
Anodier
7:
Activity of the decomposition
a
a
this, equal
empty
B
40 mg quartz wool in U-tube reactor
N02(a).
in die U-tube reactors and mounted to
to
nitrogen
8 for each reactor line. Around 550 K and at 855 K
nitrogen
respectively).
variation
and
They were pretreated as described later and experiments
distribution of the
some
dependence of
NO„(D), NO(o)
conducted witii Feed 3. The conversions of NOx
6% and 5%,
in
the
reactor
Cu0/Al203 catalyst were placed
Figure
02
was
(250 mg)
amounts
reaction of N02 to NO and
flow rate of 150 ml/min.
A
each reactor line.
about
catalyst in its position.
reactor lines. To check
the temperature with
of
fix the
experiments up to
important aspect for perfect functioning of the apparatus
equality of the three
Figure
allowed to conduct
(3%).
a
conversion could be observed
are
were
shown in
significant broader (standard deviation
The conversion of propene at 550 K showed also
At 855 K
complete
conversion of propene occured and
Chapter 2
37
no
difference could be observed. The variation of conversions
due to
dependence at these points (see also
sensitive temperature
a
profiles),
as
the conversion increased
around 550 K, and decreased
experiments, (see Table 6)
a
was
probably
temperature
strongly witii increasing temperature
markedly around
855 K. With
repeated
lower standard deviation could be obtained.
TABLE 6
Average conversions and standard deviations
CuO/Al203 catalyst with Feed 3,
N° of
average of
points
temperature
StDev of
average conv.
of
NO
conv.
aver. conv.
StDev of
of propene
propene
/%
/%
468
6
2
2
563
33
3
15
617
45
2
28
664
48
2
43
764
82
2
100
860
54
5
100
To study the influence of the amount of catalyst on the
and
on
the formation of byproducts,
Catalytic 187.5
tests with
increasing
mg) arranged in
a
reactor
increase of conversions with increasing influence
containing with
a
on
the concentration of
62.5 mg and 125 mg
reactor
containing 187.5
on
the
(62.5
mg, 125 mg and
amount of
catalyst
as
byproducts. Comparing
well
mg of the
same
in series
catalyst placed in parallel
assuming
behaviour.
Experimental
as an
two reactors
CuO(1.65), respectively, arranged
catalytic
1.
configuration showed the expected
should result in identical conversions, when
apparative characteristics
catalytic behaviour
experiments were conducted using Feed
amounts of CuO(0.78)
parallel
over a
measured with different reactor lines.
NO /%
IK
of NO and propene conversions
no
influence of
38
600
800
700
Temperature Figure
Comparison
8:
rate
D o
A
In
150
catalyst catalyst
ml(STP)/min: on
line 1
mounted
on
line 2
catalyst mounted on
line 3
9 the conversion of propene and the
depicted showing and 669 K
of reactor lines, tested with 250 mg of Cu0/Al203; Feed 3; flow
mounted
Figure
a
slightly higher activity
paragraph,
When
as
and
selectivity
the temperature
were
are
shown
vs.
Markedly higher concentrations
temperature,
error, estimated in
findings point
factor of more than 2
Chapter
of ammonia, carbon
a
different behaviour
containing 187.5
by
The
in
of ammonia and carbon monoxide
a
error.
catalysts placed
experimental
deviation of the concentrations by
experimental
are
only differed within 2 K.
measured at 669 K for the reactor
an
for the
looking at Figure 10, where die concentrations
monoxide and nitrous oxide emerges.
yield of nitrogen
similar behaviour for both reactor arrangements. At 618
series is observed. This deviation is within die the above
900
/K
2
mg
can
catalyst. This
not
to a related
be
explained
mechanism for
39
500
600
700
800
900
Temperature /K Figure 9: Influence of reactor arrangement on conversions using Feed 1 Filled symbols: 62 5 and 125 mg of catalyst CuO(l 65) (Table 9) arranged in series (reactor line 1 and 2) Open symbols: 187 5 mg of catalyst CuO(l 65) in reactor line 3
ammonia and carbon monoxide formation. Note that the temperature for the increased formation of NH3 and CO coincided wim die temperature where
maximum
catalytic activity was observed (Figure 9).
The formation of nitrous oxide did not
seem to
arrangement.
Experimental
be affected
by the
reactor
40
500
600
700
800
900
Temperature /K Figure
10:
Influence of reactor arrangement on byproduct formation using Feed 1. Filled symbols: 62.5 and 125 mg of catalyst Cu0(1.65)
(Table 9) arranged in series (reactor line 1 and 2). Open symbols: 187.5 mg of catalyst CuO(1.65) in reactor line
Chapter
2
3.
41
Catalytic
tests
873 K for 2 hours in 5% oxygen in to 473 K in
The temperature
Figure
me
nitrogen,
nitrogen. Subsequently,
passed over uie catalyst bed whh
raising
250 mg of
catalytic experiments,
Before
dependence
a
a
followed
reaction gas,
flow rate of 150
of the
as
was
pretreated
by cooling
die
catalytic behaviour
was
was
2 hours.
measured
to 873 K
as
at
catalyst
listed in Table 1,
ml(STP)/min for
temperature in steps of 50 K from 473
by
shown in
11.
Background spectra seconds witii nitrogen
were
recorded after
purging
also
Figure 4) and
100
die gas cell for 200
(3.5 l(STP)/min). Before measuring the gas mixtures at
die inlet and die outlet of uie reactors, die gas cell
(see
catalyst
two
200
spectra
300
400
were
500
was
purged for
200 seconds
measured within 400 seconds. At
600
700
800
900
1000 1100 1200
Runtime /min Figure
Course of temperature for the reactors 11: A dotted lines: reactor line 1 B
straight
line: reactor line 2
C dashed line:
reactor
line 3
Experimental
during steady
state
experiments:
42
each temperature step, the inlet concentrations
stability
vs.
time. Witii tiiree
minutes per temperature step concentrations. In 110 minutes
was
experiments
were
catalysts
were
analyzed
to
mounted in die system,
needed
to
monitor tiieir a
analyze the catalysts and me inlet
(wet feeds),
with 10% water in the feed stream
waited to allow die
total of 80
catalysts reaching
a
steady-state.
Surface Reactions of Adsorbed
Temperature-Programmed
Species
(TPSR) TPSR measurements
were
carried out to
between Uie formation of harmful precursors
exposed
die
on
350
400
a
500
possible
relation their
the 250 mg of CuO(0.78)
were
reaction mixture
450
a
byproducts (e.g. ammonia) and
catalyst surface. Therefore
for 2 hours to
investigate
(Table 7)
550
600
at a defined
650
700
temperature
750
Runtime /min Figure
12:
Course of temperature for the reactors during surface reaction
(TPSR) experiments:
A dotted lines: reactor line 1 B
straight line:
reactor line
2
C dashed line: reactor line 3
Chapter
2
temperature-programmed
800
43
and
rapidly cooled in nitrogen
men
die temperature
was
atmospheres,
specified
as
phase products
were
After
to 423 K.
reaching thermal stability,
raised at 10 K/min to 900 K
(Figure 12)
in Table 7. The concentrations of die
monitored
in various
evolving
gas
by FTIR.
TABLE 7
compositions
Feed gas
Gas
atmospheres during
for TPSR
experiments
over
CuO(0.78)
composition during loading procedure
Feedl
Feed lw
Feed 2
562, 615,661 K
615 K
615 K
TPSR 2%
2%
Oj' H20-
O,;
2%
2%
H,Ob
615 K 615 K
N2' 2%
615 K
615 K
H,'
comparative experiments, containing additionally 212 b
ppm
CH3CN
200 ppm
comparative experiments, containing additionally
or
I'OOO ppm
C^NCO.
HCN, 212 ppm CH3CN
or
r000ppmC2H5NCO. c
comparing experiments, containing additionally I'OOO ppm C2H5NCO.
For
comparison, a series of TPSR experiments was carried out in the
temperature range with CuO(0.78), pretreated with 5% Oj/Nj and then cooled
additionally The
to 463
200 ppm
a
as
specified
HCN, 212 ppm CH3CN,
concentrations
concentration at
K, using feeds
or
analyzed by FTIR do
specific temperature due
in Table 7
I'OOO ppm not
to uie time
Experimental
at 873 K
same
for 2 h
containing
C2H5NCO.
exactly reflect the
delay in recording the
44
spectra. As 200 seconds
were
needed to record
phase concentrations represent With
a
fresh
a
a
spectrum the measured gas
temperature range of about 30 K.
catalyst sample, hydrogen chloride
phase during TPSR above
823 K
originating
found in die gas
was
from chlorine residuals from die
A1C13 precursor used for the preparation of y-Al203 (Degussa, Type C). a
second run,
no
further
hydrogen chloride evolved indicating
composition. Further details
Diffuse
Reflectance
are
described in
Infrared
Chapter
Fourier
a
stable
After
catalyst
5.
Transform
(DRIFT)
Measurements DRIFT
experiments
spectrometer
equipped with
ZnSe windows within
nitrogen cooled
a
performed using
were a
Bruker IFS 55 FTIR
controlled environmental chamber fitted witii
diffuse reflectance unit
(botii Spectra-Tech),
and
a
MCT detector.
DRIFT measurements
during die temperature-programmed experiments
were
carried
Feed
lw, respectively, and rapidly cooled
were
a
out
pretreated
with catalyst
CuO(0.78) loaded in
at 615 K with Feed 1 and
nitrogen. The loaded samples
in situ in die FTIR chamber at 423 K in
nitrogen (50
ml(STPymin) for one hour and a background spectrum was taken (resolution 4
cm'1,
I'OOO
scans).
DRIFT spectra
switching to die reaction
gas mixture and
of 5 K to 773 K. Defined flows 5%
(4 cm"1,256 scans)
were
increasing me temperature
(50 mI(STP)/min) of 5%
hydrogen (TPR) in nitrogen, respectively,
were
used
compounds
(HCN and CH3CN)
ethyl isocyanate (C2H5NCO)
were
catalyst.
Chapter
2
obtained
oxygen
as
Reference spectra of pure and
recorded after in steps
(TPO) and
reactant
mixture.
by adsorbing nitriles on
the pretreated
45
Materials
Catalysts The as
catalysts
used for the
experiments
were
prepared
and characterized
described below. The metiiods used for the characterization have been
described in detail in die literature
Informations on
me
chemical
obtained from atomic
[4, 5,6,7].
composition of die catalytic systems where
absorption spectroscopy (AAS). X-ray diffraction
(XRD) provided additional information regarding die crystallinity composition
of me
total surface
area
catalysts. Nitrogen physisorption
was
used to
and
phase
measure
die
and die pore size distribution of die catalytic systems.
Cu/ZSM-5
The
ion-exchanged Cu/ZSM-5
Chemie Uetikon
0.024, SKVA1A a
=
44).
2 g of the zeohte
were
0.694, K20/A1203
=
=
washed for 20 h in 400 ml of
(purum; Fluka) solution, dried overnight under vacuum at
ion-exchanged for
Fluka) solution (90 ml, The
prepared from Na/ZSM-5 supplied by
(Zeocat PZ-2/44 Na; N^O/ALA
12 mmol NaN03
303 K, and uien
was
12
65 h wiui
a
diluted
mmol), following the metiiod
Cu(N03)2 (puriss,
of Iwamoto et al.
(8).
slurry was filtered, die resulting cake washed tiiree-times wiui deiomzed
water
and dried
The copper
overnight under vacuum at
loading
spectroscopy (AAS),
of die
was
amounted to 373
a
as
determined
2.60 wt%. BET surface
precursor Na/ZSM-5 and die
exchange did not lead to
catalyst,
303 K.
by atomic absorption
area
measurements of die
ion-exchanged catalyst indicated
significant change of the
m2/g for botii samples.
Experimental
tiiat die ion
BET surface area, which
46
A1203 The
investigations
aluminium
oxides.
were
performed using
Alumina
A,
(Alumina-C,
agglomerated with deionized water, dried and crushed to
Martinswerk)
a
two
at 393
commercially available Degussa
K, calcined in air
sieve fraction of 120-250 urn. Alumina B,
with
an
Corp.)
initial sieve fraction of 150-200
was
at 873 K
(Alumina-GX,
urn
was
treated
similarly.
TABLE 8
Characteristics of the alumina based
Catalysts
"
b
CuO-loading*
BET surface
catalysts
sieve fraction
area
XRD
[wt%]
K/g]
[umj
alumina A
-.-
109
120-250
100%
alumina B
-.-
100
150-200
90%
y-AljOj/
10%
o-Al20,
CuO(0.46)
0.46
CuO(0.78)
0.78
CuO(1.65)
1.65
copper
101
loadings expressed as CuO,
value in
120-250
100%
Y-A1203
106
120-250
100%
y-AljOj
103
120-250
100%
Y-A1203
determined
by
AAS.
parenthesis correspond to a repeated measurement.
BET surface
amounted to 109
corresponding
areas
m2g''
determined by
alumina B
was
nitrogen adsorption
for alumina A and 100
average pore diameters of 29
analysis showed for alumina
as
(107)"
y-Al203
A
nm
m2g''
made up of approximately 90 %
listed in Table 8.
Chapter 2
for alumina B, with
and 9 nm,
only reflections due
measurements
to
respectively.
XRD
y-A1203, whereas
y-alumina and
10 %
-
1—
800
700
Temperature Figure
7:
900
/K
Temperature dependence of conversion of NO to nitrogen for (A) Feed 2 and (B) Feed 2w (Table 1;
Chapter 2). (T) A1203, (o) CuO(0.46), (a) CuO(0.78), () CuO(1.65); total flow rate, ml(STP)/min; catalyst weight, 250 mg.
Figure and
C02
8
150
depicts die temperature dependence of the formation of CO, NH3
for the TPSR in 2 %
Feed 1 at 562, 615 and 661 K,
Oj/Nj using sample CuO(0.78)
respectively. Production of other
products such as HCN or N20 was neghgible during TPSR in 2
sample
loaded with
loaded at 615 K showed the
largest
amount
Copper-alumina catalysts
of gas
%
gas
phase
Q>J\$2.
The
phase products
106
formed, indicating highest loading of the catalyst with adsorbates For
loading temperatures exceeding 661 products
gaseous
nitrogen yield during reaction with
Comparing
surface.
the
a
steady decrease in the
C02 and NH3
Feed 1
were
NH3
are
CuO(0.78), only low
over
measured, indicating
the relative amounts of products
highest proportion, followed by CO, and,
of 45 ppm,
amount of
found and for 765 K, tiie temperature of maximum
was
concentrations of CO,
K
deposits.
or
with
a
almost clean
an
formed, C02 represents maximum concentration
NH3. The temperatures of maximum formation of CO, C02, and
comparable
for identical
loading temperatures
and
are
shifted to
higher
temperatures for increasing loading temperatures. The temperature window of
NH3 fonnation during TPSR (Fig. 8B) coincides
catalytic
tests
witii the
one
observed in the
(see Figure 2).
No ammonia formation and
ppm) and C02 (396 ppm)
substantially lower concentrations of CO (100
were
observed when
CuO(0.78)
was
loaded witii
Feed lw at 615 K. This
indicates, tiiat the presence of water suppresses the
formation of deposits
the
on
catalyst surface, which moreover do
precursor
species for NH3 formation.
CuO(0.78)
loaded at 615 K with
propene resulted in less
C02 (133 ppm) found in the
Figure
9 shows die
02, H20,
or
conducted witii
produced
H20
over a
as
-
evolution from
as
CuO(0.78) loaded
different gas mixtures
containing
reactive components. With 2%
wide temperature range
maximum of 47 ppm at 648 K. In the
in the temperature range 580
well
2.
comparison of NH3
+
as
at 652 K. Note that no ammonia was
during TPSR in diree
02
contain
containing ethene (Feed 2) in place of
(34 ppm), all
catalytic tests with Feed
ammoma was a
feed
experiments
pronounced evolution of ammonia (7 ppm),
and CO
at 615 K with Feed 1
either
a
TPSR
not
800 K,
case
of 2 %
peaking
Chapter
5
starting
Oj/Nj,
H20/N2,
at 520 K with
ammonia
appeared
at 707 K with 45 ppm.
Using
107
500
600
700
Temperature/ Figure
8:
Comparison
of formation of (A) carbon monoxide,
and (C) carbon dioxide
programmed
vs.
690
K, indicating
in
(B) ammonia,
temperature for temperature-
0^2 of CuO(0.78) loaded Chapter 2) at different temperatures. ()
loaded at 562 K, (o) loaded
H20
900
surface reaction in 2 %
with Feed 1 (Table 1;
both 2% 02 and 2%
800
K
nitrogen
two reaction
at
615 K and (A) loaded at 661 K.
two maxima were
pathways leading
Copper-alumina catalysts
to
observed
at 608 K and
NH3. Table
1 hsts the
108
products
during the
observed
atmospheres, including
2 %
H2/N2.
species as being the primary
source
of ammonia formation,
using acetonitrile and ethyl isocyanate
added to
a
TPSR feed
depicted in Figure
10A for
containing
comparable
to the one
Furthermore,
as
are
is
observed
at 575 K
produced
over
appears in the
found in
Fig. 9,
02
Fig.
(2020 ppm)
+
as a
9 for the
and at 700 K
single peak In
maximum of 43 ppm at 640 K
2 %
are
used in
evolution of ammonia starting at
peaks
appear at 545 K
ammonia ca.
peak.
60 K to
K
in
H20
sample loaded
(1890 ppm).
nitrogen
-
are
02/N2.
800
K)
with Feed 1.
was
Carbon dioxide
whereas CO
investigated,
(770 ppm) simultaneously
at 700 K
addition,
small amount of HCN witii
a
detected. Note that this temperature
place
of ethyl
picture
isocyanate (Fig.
(216 ppm).
at 640 K
a
lays
emerges when
1
IB),
slightly lower temperature (480 K).
(295 ppm) and
formation, peaking at 640
etfryl isocyanate
h at 873 K in 5%
within the two maxima of ammonia fonnation. A similar 212 ppm acetonitrile
compounds. The
temperature range (500
a
die whole temperature range
NH3 peak.
model
were
clearly discernible peaks of ammonia formation
two
product gas
with the second
2 %
experiments
1000 ppm
CuO(0.78) pretreated for 2
Ammonia formation takes place in
in
as
C02 and NH3 produced when
concentrations of CO, was
gas
investigate the possibility of surface cyanide and/or isocyanate
In order to
carried out
experiments using different
TPSR
with the
Two
NH3
Note that CO
(320 ppm), is again overlapping with die second
The onset temperature for
C02 and
higher temperatures compared
to
CO formation is shifted
die
by
NH3 formation. The high
concentrations found for die low temperature
peak of ammonia, thus exceeding
the feed concentrations of the
and nitrile
reactions of adsorbates
or
isocyanate
deposits formed
at lower
in the fonnation of NH3.
Chapter 5
species, indicate that
temperatures
are
involved
f
ata
r-alumn
«»
£ S
C,H4
-
.
513-699
20 770
-
611-855
H,0
547
474-855
-
513-784
124 569
770
511-855
506
646
445-874
547-855
513-757
-
244
714
517-874
CO,
-
1020
679
550-779
CO
-
81
646-842
NO -
474-855
611
4 19
779
517-615
-
725 8
-
669
318
669
669
-
12 480 -
39 669
738
545-757
9 13
675
580-738
45
707
S84-811
415-545
[KJ
[ppm]
575
HCN
NH,
cone
H,0/N, max
2%
[ppm]
T-max
PC]
T-range
+
at 615 K with Feed 1
TPSR with 2% O,
[KJ
cone
[K|
T-range max
2%H,/N,
T-max
TPSR with
CuO(0 78) loaded
[ppm]
cone
over
[K]
max
TPSR measurements
[K]
T-range
T-max
0,/N,
phase components during
TPSR with 2%
Concentrations of gas
TABLE 1
110
Performing 2 %
02
2 %
or
containing
the
same
experiments
witii
a
reactant gas
H20 in nitrogen results in single
gas mixture
whereas two ammonia
(616
peaks
K for were
ammonia
etiiyl isocyanate,
containing either
peaks
for die water
575 K for
acetonitrile),
observed for the oxygen
containing feed
at
i—i—i—i—i—.—i——i—i—i—.—i—,—i—i—i—,—] 50-
F o
,
Q.
40-
r>
i 30-
"6
2? o
?n-
-hi j=
'
c
10-
o
