Effect of transition metal on stability and activity of La

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 4 2 ( 2 0 1 7 ) 1 9 9 2 0 e1 9 9 3 4

Available online at www.sciencedirect.com

ScienceDirect journal homepage: www.elsevier.com/locate/he

Effect of transition metal on stability and activity of La-Ca-M-(Al)-O (M ¼ Co, Cr, Fe and Mn) perovskite oxides during partial oxidation of methane Jaroslav Cihlar Jr.*, Radimir Vrba, Klara Castkova, Jaroslav Cihlar CEITEC - Central European Institute of Technology, Brno University of Technology, Purkynova 656/123, 612 00 Brno, Czech Republic

article info

abstract

Article history:

Perovskite oxides of the type of LaxCa1-xMyAl1-yO3-d (M ¼ Co, Cr, Fe, Mn; x ¼ 0.5; y ¼ 0.7e1.0)

Received 12 April 2017

were prepared using the polymerization methods and evaluated via N2 adsorption, X-ray

Received in revised form

diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning transmission electron

3 June 2017

microscopy (STEM), energy dispersive X-ray (EDX) spectroscopy, temperature-programmed

Accepted 8 June 2017

reduction by hydrogen (TPR-H2) and temperature-programmed oxidation by oxygen (TPO-

Available online 4 July 2017

O2). Catalytic behaviour of the perovskite oxides during methane oxidation was studied using a tubular fixed-bed reactor. In a partial oxidation, which proceeded in two steps,

Keywords:

there was total oxidation in the first step and CO2 and H2O were formed; in the second step,

Lanthanum perovskite oxides

the total oxidation products oxidized methane by (dry and wet) reforming reactions to yield

Methane

CO and H2. Total oxidation and the two reforming reactions proceeded on two types of an

Catalytic partial oxidation

active centre formed by transition metal ions, oxygen vacancies and oxide ions. The cat-

Transition metals

alytic system La-Ca-Co-Al-O which contained aluminium, decomposed in partial oxidation

Syngas

of methane (POM) into a composite that contained firmly bonded cobalt nanoparticles in the surface of a substrate made up of La2O3, CaO and Al2O3 which catalysed POM with a high methane conversion and hydrogen selectivity. © 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

Introduction Partial oxidation (POM) and reforming of methane rank among significant methods for the generation of syngas, which is important not only in the Fischer-Tropsch syntheses but also as fuel and source of hydrogen for heat machines and fuel cells [1e4]. The most active and industrially most widespread are POM catalysts based on very expensive precious metals (Rh, Pt, Pd) and supported on alumina, zirconia or magnesia substrates [5e9]. The cheaper POM catalysts based on

common transition elements (such as Ni, Co, Fe, Mn and Cr) have therefore been the subject of long-standing intensive research [9e14]. Complex perovskite oxides based on the oxides of lanthanides, alkaline earth metals and 3d-transition metals are the most promising candidates for electrochemical and catalytic applications [15]. In these oxides of the general formula Ax A0 1x By B0 1y O3 , the content of the oxide vacancies ðVO Þ can be influenced by substituting for lanthanide cations at site A while substituting for transition element cations at site B. By this process the redox behaviour and stability of the complex

* Corresponding author. E-mail address: [email protected] (J. Cihlar). http://dx.doi.org/10.1016/j.ijhydene.2017.06.075 0360-3199/© 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.


perovskites can be influenced [16]. Perovskite substitution in a wide range of ion concentrations at sites A and B makes it possible to modify the composition, structure and thus oxygen stoichiometry and catalytic activity of perovskites in oxidation reactions. The oxygen vacancy, formed by substituting La3þ ions by lower valence ions or by the reduction of perovskites in the course of methane oxidation, can be re-filled with active oxygen by chemisorption of gaseous oxygen from the reaction medium in the current catalyst regeneration. Cyclic oxidation and reduction of the catalyst system associated with the oxidation of methane proceeds usually according to the Mars-Van Krevelen mechanism (MVK) [17]. Perovskite oxides containing Co (or Ni) are only precursors of active catalysts. In the reduction atmosphere during POM, perovskites decompose into a catalytically active mixture of oxides with finely dispersed metal particles on the surface [12]. Strong metal-support interaction between reduced Ni and oxide support (Ca-Sr-Ti-O) increased the catalytic activity and stability of the catalyst since it retarded the coke formation [18]. A similar effect was also described for cobaltites. Lago et al. [11] found that catalytic activity of CoO/Ln2O3 (Ln¼La, Nd, Sm, Gd) formed by the reduction of LnCoO3 decreased with increasing perovskite stability in the reduction. The more stable perovskites (LnCoO3) were easily deactivated by reoxidation. Deactivation can also occur due to the reaction of basic rare earths with water [11,19]. Perovskite cobaltites provide catalytic systems achieving almost 100% methane conversion and over 90% hydrogen selectivity [11,20,21]. A comparison with catalysts of POM derived from perovskite ferrites, manganites and chromites is difficult because comparable literature data obtained under similar conditions are scarce. In the catalysis of POM by the perovskite La1xSrxFeO3-d (x ¼ 0.0e0.6) [22] obtained 95% methane conversion while Khine et al. [23] came to 65%, but there was considerable methane cracking. This is probably the main reason why POM via perovskite ferrites is performed using the chemical looping method [24e30]. Using this method gives high yields but this is in fact not a catalytic process but two separate (s)-(g) reactions between perovskite ferrite and methane or oxygen. Wei et al. [31] used the pulsing method, which is similar to the chemical looping method, to study the reduction of LaMnO3 manganite by methane, and obtained a methane conversion of ca 20%. Modifying manganite by ruthenium (Rh/LaMnO3) yielded 90% methane conversion and 97% hydrogen selectivity [32]. For perovskite chromites, too, a low methane conversion (10%) [23] was established. Ruthenium doping of chromites increased the conversion of partial oxidation (POX) of diesel to 95%. Scattered literature data, however, do not allow drawing a definite conclusion as to the catalytic behaviour of perovskite oxides containing Co, Cr, Fe, and Mn in partial oxidation of methane. This topic, in particular the study of catalytic behaviour of transition elements in perovskites and their effect on the mechanism of POM, deserves serious attention. The present work therefore focuses on the study of the effect of the transition metal M (Co, Cr, Fe and Mn) in model perovskite systems La-Ca-M-(Al)-O of two types, La0.5Ca0.5MO3-d and La0.5Ca0.5M0.7Al0.3O3-d, on their catalytic activity in POM.

19921

Since in catalytic tests, temperature-programmed reduction (TPR) or temperature-programmed oxidation (TPO) the chemical and phase compositions of practically all perovskites changed, such decomposed perovskites are in the present work referred to as a “La-Ca-M-(Al)-O (M ¼ Co, Cr, Fe, Mn) system” instead of using the chemical name for the starting as-prepared perovskite.

Experimental Syntheses of perovskite oxides Powder oxides of the perovskite structure La0.5Ca0.5MO3d (M ¼ Co, Cr, Fe, Mn) were prepared by the Pechini method [33]. Starting substances were Ca(NO3)2$4H2O p.a. (99%, Lachema), Fe(NO3)3$9H2O p. a. (98%, Sigma-Aldrich), Al(NO3)3$9H2O p. a. (98%, Sigma-Aldrich), Co(NO3)2$6H2O p. a. (99%, Hichem), Mn(NO3)2$4H2O p. a. (97%, Sigma-Aldrich), Cr(NO3)3$9H2O p. a. (98%, Hichem), citric acid p. a. (99.8%, Onex), ethylene glycol p. a. (99.5%, Lachner) and potato starch (Sigma eAldrich). With the Pechini method, the starting substances were successively dissolved in distilled water heated to 80 C, in the following order: lanthanum nitrate, calcium nitrate, citric acid, ethylene glycol, and eventually the respective nitrates of transition metals, depending on the type perovskite being prepared. The molar ratio of citric acid/nitrates ¼ 3 and molar ratio of citric acid/ethyleneglycol ¼ 1. The molar ratio of the M (Co2þ, Mn2þ, Cr2þ), Ca2þand La3þ cations was Fe2þ, La:Ca:M ¼ 0.5:0.5:1. After re-filtering this solution, water and the other liquid phases were distilled off, with solid porous amorphous yellow, grey to black substance being formed. This solid substance was ignited in order to remove the organic component. The porous gel, formed by polycondensing a solution of citric acid and ethylene glycol, and containing homogeneously dispersed cations, was pyrolysed at 300 C, milled and calcined in air at 800 C/7 h. A combined carbohydrate-mechanochemical method was used to prepare a perovskite of the general composition La0.5Ca0.5M0.7Al0.3O3-d (M ¼ Co, Cr, Fe, Mn). The essence of the method consisted in mechanochemical homogenization of a mixture of La, Ca, Al, Co, Cr, Mn and Fe oxides in the molar ratio La:Ca:Al:M ¼ 0.5:0.5:0.3:0.7. Eight times the amount of starch was added to the mixture of nitrates in the molar ratio given above. The suspension formed was milled for 24 h in a planetary mill in the presence of 150 ml ethylene glycol. The resulting viscous substance was burnt at 300 C and the organic components and ethylene glycol contained in the substance were removed. The ash obtained was milled and then calcined in a furnace at 1000 C/24 h.

Characterization of perovskite oxides The La0.5Ca0.5MO3-d and La0.5Ca0.5M0.7Al0.3O3-d (M ¼ Co, Cr, Fe, Mn) perovskite oxides were evaluated via nitrogen adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM),

19922


energy dispersive X-ray (EDX) spectroscopy, temperatureprogrammed reduction by hydrogen (TPR-H2) and temperature-programmed oxidation by oxygen (TPO-O2). The phase composition of perovskite particles was determined by the X'pert RTG diffractometer (Philips) in a central focusing configuration, using CoKa radiation and two types of detectors e X'celerator and Microprobe. The corresponding standards were established by comparing the ICSD (Inorganic Crystal Structure Database, FIZ). The crystallographic structures and quantitative phase-analysis were assessed using the Highscore program (PANalytical). The data were entered into the algorithm according to Rietveld [34] and mathematically processed to completely cover the measured diffractogram. The morphology of the perovskite particles (particle shape and size) and their chemical composition were evaluated on a scanning electron microscope SEM XL30-EDAX (Philips) equipped with energy dispersion XRD spectrometer. The specific surface of perovskites was measured on a CHEMBET 3000 device (Quantachrome) and, using the BET method, evaluated from the adsorption isotherms of nitrogen measured at 77 K on samples degassed at 300 C. Detailed morphologies and chemical composition of the La-Ca-Co-O system after tests of POM were established using the TITAN Themis 60-300 device (FEI) at an acceleration voltage of 300 kV. The composition was analysed via EDS mapping with the aid of a SUPER-X detector, with subsequent processing by the Esprit 1.9 software (Bruker). Structural imaging was performed using a STEM detector of the HAADF (high angle annular dark field) type. X-ray photoelectron spectroscopy (XPS) of the La-Ca-Co-O system reduced in the course of POM was carried out using Kratos Axis Supra (Kratos-XPS), with monochromatic Ka radiation, 300 W emission power, magnetic lens and the charge compensation turned on. The survey and detailed spectra were measured using pass energies of 160 and 20 eV, respectively). The spectra were evaluated using the Unifit 2013 software. The TPR-H2 and TPO-O2 profiles were measured on the Catlab device (Hiden Analytical Ltd.) (details are given in Supplementary information). Simultaneous thermal analysis of the La-Ca-Co-O perovskite system was measured on STA 409 CD/QMS 403 Skimmer (Netzsch) in reduction and oxidation atmospheres (details are given in Supplementary information).

Tests of catalytic activity of La-Ca-M-(Al)-O systems The catalytic activity of perovskites during the oxidation of methane by gaseous oxygen was tested in a tubular fused silica reactor with fixed catalytic bed, placed in a horizontal tubular furnace (Fig. 1S, details are given in Supplementary information). The methane conversion XCH4, oxygen conversion XO2, selectivity Si, and yield Yi of CO, CO2, H2 and H2O were evaluated using Eqs. (1)e(8), where F0CH4 and F0O2 represents the molar flow of methane and oxygen [mmol s1] in the input of the reactor, and Fi (i ¼ CH4, O2, CO, CO2, H2 and H2O) represents the molar flow of reactants and products in the output of the reactor. XCH4 ¼

FoCH4 FCH4 $100 ½% F0 CH4

(1)

XO2 ¼

FoO2 FO2 $100 ½% F0 O2

(2)

SCO ¼

FCO $100 ½% FCO þ FCO2

(3)

FCO2 $100 ½% FCO þ FCO2

SCO2 ¼

SH2 ¼

FH2 $100 ½% FH2 þ FH2O

SH2O ¼

FH2O $100 ½% FH2 þ FH2O

(4)

(5)

(6)

YH2 ¼

SH2 $XCH4 ½% 100

(7)

YCO ¼

SCO $XCH4 ½% 100

(8)

Results Structure of La-Ca-M-(Al)-O perovskites The lattice parameters of La-Ca-M-(Al)-O perovskite oxides are given in Table 1. In the first group, 50% of La3þ ions in the basic LaMO3 lattice were substituted with Ca2þ ions. In the second group, 50% of La3þ ions in the lattice were substituted with Ca2þ ions, and 30% of Mzþ ions (Co, Cr, Fe, Mn) were substituted with Al3þ ions. Since the molar concentrations of La3þ and Ca2þ or La3þ, Ca2þ, Al3þ in the La-Ca-M-O or La-Ca-M(Al)-O perovskites are similar, the difference in the crystal structure should primarily depend on the type (and content) of the transition metal M. The ideal undoped ABO3 (LaMO3) perovskite containing a B-cation with coordination number CN ¼ 6, an A-cation with CN ¼ 12, and an O-anion with CN ¼ 2 should have a cubic lattice [35] when the so-called Goldschmidts' tolerance factor t ¼ 1 [36]. However, the t-factor of perovskites may lie in a wide range from 0.75 to 1, and the LaMO3 perovskite can generally crystallize in an arbitrary lattice [37]. The t-factor values for the La-Ca-M-(Al)-O perovskites given in Table 1S (Supplementary data) are in the range from 0.89 to 1.02. The La-Ca-M-(Al)-O perovskites, the crystallography data of which are given in Table 1, crystallized in the orthorhombic (Pnma or Pbnm) or rhombohedral (R3c) lattice. Diffraction spectra of the La-Ca-M-(Al)-O as prepared perovskites before (BT) POM testing are given in Figs. 2S and 3S, (Supplementary data). If we compare the crystallography data of basic LaMO3 perovskites taken from the literature and the crystallographic data of doped La-Ca-M-O perovskites (Table 1), we can see that the type of the crystal structure of the basic LaMO3 perovskites [38,39] remained preserved in practically all doped La-Ca-M-O perovskites. In all the four perovskites, some parameters of the crystal lattices were reduced and their volume decreased. This effect relates to the substitution of 50% of La3þ ions with Ca2þ ions, whose ion A a radius is smaller than that of La3þ (rLa3þ ¼ 1.36 A). The doping of La-Ca-M-O perovskites in rCa2þ ¼ 1.34

19923


Table 1 e Crystallographic data of La-Ca-M-(Al)-O perovskites (as prepared). Perovskite system

Lattice parameters [ A]

Lattice

Content

Volume

type

a

b

c

[wt %]

[nm3]

La-Ca-CoO La-Ca-Fe-O La-Ca-Cr-O La-Ca-Mn-O La-Ca-Al-Co-O La-Ca-Al-Fe-O La-Ca-Al-Cr-O La-Ca-Al-Mn-O

R3c Pnma Pnma Pnma R3c Pbnm Pnma Pbnm

5.4005 5.4846 5.4600 5.4337 5.3932 5.4656 5.3808 5.3903

5.4005 7.7878 7.7280 7.7103 5.3932 5.4631 7.6031 5.3758

13.1812 5.5050 5.4905 5.4690 13.1054 7.7278 5.4108 7.5728

99.5 100 La-Ca-Cr-(Al)-O, i.e. with increasing stability of the La-Ca-M-(Al)-O systems during reduction by hydrogen (see Sec. 3.2) or with increasing strength of the MeO bond in perovskites [43,44]. With the MVK mechanism the reaction rate is primarily dependent on the thermodynamic strength of the MeO bond but it also depends on kinetic parameters (T, pCH4, pO2) and, above all, on the number of active sites on the catalyst surface. In the description of active centre a model of stable perovskite structure is used which contains different types of oxygen bonded in the surface layers or in the volume in the form of

Fig. 8 e STEM-EDS mapping images of chemical elements for La-Ca-Cr-Al-O system after POM test (the green colour indicates Cr and pink Ca). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

19931

Fig. 9 e XPS spectrum of the Cr2p core level of La-Ca-Cr-AlO system after POM test.

[55] and oxygen vacancies near the transition O2, O2 2 , O metal. The description holds good in the case of a perovskite structure that does not decompose in the catalytic test. In POM taking place in the tube reactor, where perovskite is in the presence of both the reduction agent CH4 and the oxidation agent O2, perovskite generally is not stable. Most papers and also this work indicate that Co-based perovskite decomposes into Co particles, which segregate on the surface of irreducible oxides, La2O3, CaO, Al2O3 etc. and the catalysis of POM does not proceed on a perovskite structure and thus the active centre cannot be thought of as a site on the perovskite structure containing oxygen, vacancies and transition metal. Similarly, in POM the La-Ca-Fe-(Al)-O perovskites decompose, giving rise to particles of Fe0, iron oxides and irreducible oxides of the other elements contained in perovskite. Even on decomposed perovskites, however, oxidation of methane could proceed by a mechanism proposed by Mihai et el [68]. for the structurally stable perovskite LaFeO3. The catalysis of TOM, POM and MP (methane pyrolysis) can occur on one type of a structurally similar active centre containing transition metal (Co, Fe) and its oxide with a varied number of O coordinated in its vicinity. The centre containing metal with a high coordination number (CN) catalysed TOM, that with medium CN catalysed POM, and that with low CN catalysed the methane pyrolysis. Out of all the systems under study, the catalytic activity (conversion, selectivity and yield during POM) of this type of centre, containing metal nanoparticles Co0 and Fe0, was the highest. It was only at this type of centre that the methane pyrolysis occurred (Fig. 12). The simultaneously occurring TOM and POM at 850 C showed that methane oxidation catalysed by La-Ca-Cr-(Al)-O and La-Ca-Mn-(Al)-O perovskites was taking place simultaneously on two types of active site containing metal ions (Mnzþ, Crzþ) with different numbers of superficial oxygen atoms and vacancies in close neighbourhood. Crzþ ions on the surface of stable La-Ca-Cr-(Al)-O perovskite with superficially bonded oxygen and oxygen vacancies in close neighbourhood

19932


Fig. 10 e A, B Effect of the reaction temperature on pO2 and pH2 in the products of POM catalysed by La-Ca-M-(Al)-O perovskite systems.

Fig. 11 e Relation between pO2 and YH2 in the products of POM catalysed by La-Ca-M- (Al)-O perovskite systems.

of Crzþ can also serve as active centres in POM. The high stability and low mutual oxygen exchange in perovskite manganites and chromites in the reduction processes are the main cause of their low activity in POM. The comparison of catalytic activity of La-Ca-Cr-(Al)-O perovskite with the most active La-Ca-Co-(Al)-O system is evident from time-on-stream test given in Fig. 21S in Supplementary information. The MVK mechanism of partial oxidation of methane catalysed by reduced La-Ca-M-(Al)-O systems can be expressed € ger-Vink notation [69] given in Supplementary using the Kro information. Based on TPR/TPO experiments and catalytic tests in fixed-bed reactor, partial oxidation of methane catalysed by La-Ca-M-(Al)-O systems can be interpreted via a twostep mechanism. In the first step, the total oxidation of methane occurred and in the second step, products of the total oxidation reacted with methane to give CO and H2 by stream and dry reforming reactions.

Conclusions

Fig. 12 e Effect of the reaction temperature on pH2/pCO in the products of POM catalysed by La-Ca-M-(Al)-O perovskite systems.

With the exception of the La-Ca-Cr-(Al)-O system the transition element was partially or completely reduced in TPR-H2 and the perovskite structure decomposed. Reoxidation of decomposed La-Ca-M-(Al)-O systems did not restore the original single-phase structure of perovskites. Partial oxidation of methane in catalytic tubular fixed-bed reactor can be described by a two-step mechanism. At the reactor input, the total oxidation of methane took place while deeper in the reactor at a partial oxygen pressure of units of Pa the water and carbon dioxide reformation of methane to syngas occurred. The catalysis of POM probably proceeded on a different type of active centre than TOM. Catalytic activity did not depend directly on a specific surface but on the amount of accessible active sites on the catalyst surface. The structure of the active sites was dependent on the type of transition element in perovskite or on its reducibility. The highest catalytic activity in POM was established for La-Ca-Co-(Al)-O perovskite systems which decomposed by reduction to composite of metal nanoparticles (Co0) bounded on the surface of irreducible oxides (La2O3, CaO, Al2O3).


Acknowledgements This research was conducted under the CEITEC 2020 (ID number LQ1601) project, with financial support from the Ministry of Education, Youth and Sports of the Czech Republic under National Sustainability Programme II. Part of the work was carried out with the support of the core facilities of the CEITEC open access project, ID number LM2011020, funded by the Ministry of Education, Youth and Sports of the Czech Republic under the activity “Projects of major infrastructures for research, development and innovations”. The authors would also like to thank Dr. Spotz, Dr Polcak, Dr. Kalina and Michalicka, MSc. who provided the XRD, XPS and SEM/TEM measurements.

Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ijhydene.2017.06.075.

references

~ a MA, Fierro JLG. Chemical structures and performance of [1] Pen perovskite oxides. Chem Rev 2001;101:1981e2017. [2] Dai XP, Wu Q, Li RJ, Yu CC, Hao ZP. Hydrogen production from a combination of the water-gas shift and redox cycle process of methane partial oxidation via lattice oxygen over LaFeO3 perovskite catalyst. J Phys Chem B 2006;110:25856e62. [3] van den Bossche M, McIntosh S. Rate and selectivity of methane oxidation over La0.75Sr0.25CrxMn1-xO3-d as a function of lattice oxygen stoichiometry under solid oxide fuel cell anode conditions. J Catal 2008;255:313e23. [4] Irvine JTS, Neagu D, Verbraeken MC, Chatzichristodoulou C, Graves C, Mogensen MB. Evolution of the electrochemical interface in high-temperature fuel cells and electrolysers. Nat Energy 2016;1. [5] Enger BC, Lodeng R, Holmen A. A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts. Appl Catal a-Gen 2008;346:1e27. [6] Pompeo F, Nichio NN, Ferretti OA, Resasco D. Study of Ni catalysts on different supports to obtain synthesis gas. Int J Hydrogen Energ 2005;30:1399e405. [7] Liu HM, He DH. Recent progress on Ni-Based catalysts in partial oxidation of methane to syngas. Catal Surv Asia 2012;16:53e61. [8] Rodrigues LMTS, Silva RB, Rocha MGC, Bargiela P, Noronha FB, Brandao ST. Partial oxidation of methane on Ni and Pd catalysts: influence of active phase and CeO2 modification. Catal Today 2012;197:137e43. [9] Dedov AG, Loktev AS, Komissarenko DA, Parkhomenko KV, Roger AC, Shlyakhtin OA, et al. High-selectivity partial oxidation of methane into synthesis gas: the role of the redox transformations of rare earth - alkali earth cobaltatebased catalyst components. Fuel Process Technol 2016;148:128e37. [10] de Araujo GC, Lima S, Rangel MD, La Parola V, Pena MA, Fierro JLG. Characterization of precursors and reactivity of LaNi1-xCoxO3 for the partial oxidation of methane. Catal Today 2005;107e108:906e12.

19933

[11] Lago R, Bini G, Pena MA, Fierro JLG. Partial oxidation of methane to synthesis gas using LnCoO3 perovskites as catalyst precursors. J Catal 1997;167:198e209. [12] Slagtern A, Olsbye U. Partial oxidation of methane to synthesis gas using La-M-O catalysts. Appl Catal A General 1994;110:99e108. [13] Silva CRB, da Conceicao L, Ribeiro NFP, Souza MMVM. Partial oxidation of methane over Ni-Co perovskite catalysts. Catal Commun 2011;12:665e8. [14] Vella LD, Villoria JA, Specchia S, Mota N, Fierro JLG, Specchia V. Catalytic partial oxidation of CH4 with nickellanthanum-based catalysts. Catal Today 2011;171:84e96. [15] Taguchi H, Masunaga Y, Hirota K, Yamaguchi O. Synthesis of perovskite-type La1xCaxFeO3 (0 x 0.2) at low temperature. Mater Res Bull 2005;40:773e80. [16] Merino NA, Barbero BP, Cellier C, Gamboa JA, Cadus LE. Effect of the calcium on the textural, structural and catalytic properties of La1-xCaxCo1-yFeyO3 perovskites. Catal Lett 2007;113:130e40. [17] Mars P, van Krevelen DW. The Proceedings of the Conference on Oxidation Processes Oxidations carried out by means of vanadium oxide catalysts. Chem Eng Sci 1954;3:41e59. [18] Hayakawa T, Harihara H, Andersen AG, Suzuki K, Yasuda H, Tsunoda T, et al. Sustainable Ni/Ca1xSrxTiO3 catalyst prepared in situ for the partial oxidation of methane to synthesis gas. Appl Catal A General 1997;149:391e410. [19] Marcos JA, Buitrago RH, Lombardo EA. Surface chemistry and catalytic activity of La1 yMyCoO3 perovskite (M ¼ Sr or Th). J Catal 1987;105:95e106. [20] Morales M, Espiell F, Segarra M. Performance and stability of La0.5Sr0.5CoO3-d perovskite as catalyst precursor for syngas production by partial oxidation of methane. Int J Hydrogen Energ 2014;39:6454e61. [21] Dedov AG, Loktev AS, Komissarenko DA, Mazo GN, Shlyakhtin OA, Parkhomenko KV, et al. Partial oxidation of methane to produce syngas over a neodymium-calcium cobaltate-based catalyst. Appl Catal A General 2015;489:140e6. [22] Zhao K, He F, Huang Z, Zheng AQ, Li HB, Zhao ZL. La1-xSrxFeO3 perovskites as oxygen carriers for the partial oxidation of methane to syngas. Chin J Catal 2014;35:1196e205. [23] Khine MSS, Chen LW, Zhang S, Lin JY, Jiang SP. Syngas production by catalytic partial oxidation of methane over (La0.7A0.3BO3 (A ¼ Ba, Ca, Mg, Sr, and B ¼ Cr or Fe) perovskite oxides for portable fuel cell applications. Int J Hydrogen Energ 2013;38:13300e8. [24] Mihai O, Chen D, Holmen A. Chemical looping methane partial oxidation: the effect of the crystal size and O content of LaFeO3. J Catal 2012;293:175e85. [25] Li KZ, Wang H, Wei YG. Syngas generation from methane using a chemical-looping concept: a review of oxygen carriers. J Chem-Ny 2013:1e8. [26] Zeng Y, Tamhankar S, Ramprasad N, Fitch F, Acharya D, Wolf R. A novel cyclic process for synthesis gas production. Chem Eng Sci 2003;58:577e82. [27] Neal L, Shafiefarhood A, Li FX. Effect of core and shell compositions on MeOx@LaySr1-yFeO3 core-shell redox catalysts for chemical looping reforming of methane. Appl Energ 2015;157:391e8. [28] He F, Li XN, Zhao K, Huang Z, Wei GQ, Li HB. The use of La1xSrxFeO3 perovskite-type oxides as oxygen carriers in chemicallooping reforming of methane. Fuel 2013;108:465e73. [29] Evdou A, Zaspalis V, Nalbandian L. La1-xSrxFeO3-d perovskites as redox materials for application in a membrane reactor for simultaneous production of pure hydrogen and synthesis gas. Fuel 2010;89:1265e73. [30] Dai XP, Yu CC. Nano-perovskite-based LaMO3 oxygen carrier for syngas generation by chemical-looping reforming of methane. Chin J Catal 2011;32:1411e7.

19934


[31] Wei HJ, Cao Y, Ji WJ, Au CT. Lattice oxygen of La1-xSrxMO3 (M ¼ Mn, Ni) and LaMnO3-aFb perovskite oxides for the partial oxidation of methane to synthesis gas. Catal Commun 2008;9:2509e14. [32] Barbato PS, Landi G. Partial oxidation and CO2-ATR of methane over Rh/LaMnO3 honeycomb catalysts. Catal Lett 2010;137:16e27. [33] Pechini MP. Method of preparing lead and alkaline earth titanates and niobates and coating method using the same to form a capacitor. Patent US 3330697 A; 1967:7p. [34] Rietveld HM. A profile refinement method for nuclear and magnetic structures. J Appl Crystallogr 1969;2:65e71. [35] Gupta S, Mahapatra MK, Singh P. Lanthanum chromite based perovskites for oxygen transport membrane. Mater Sci Eng R Rep 2015;90:1e36. [36] Goldschmidt VM. Die Gesetze der Krystallochemie. Naturwissenschaften 1926;14:477e85. [37] Levy MR. Crystal structure and defect property predictions in ceramic materials [a dissertation submitted to the University of London for the degree of Doctor of philosophy and the Diploma of imperial college]. London: University of London, Imperial College of Science, Technology and Medicine; 2005. [38] Chiba R, Yoshimura F, Sakurai Y. An investigation of LaNi1xFexO3 as a cathode material for solid oxide fuel cells. Solid State Ionics 1999;124:281e8. [39] Gupta S, Mahapatra MK, Singh P. Phase transformation, thermal expansion and electrical conductivity of lanthanum chromite. Mater Res Bull 2013;48:3262e7. [40] Miniajluk N, Trawczynski J, Zawadzki M, Tomaszewski PE, Mista W. Solvothermal synthesis and characterization of mixed oxides with perovskite-like structure. Catal Today 2015;257:26e34. [41] Tien-Thao N, Alamdari H, Kaliaguine S. Characterization and reactivity of nanoscale LaCo,CuO3 perovskite catalyst precursors for CO hydrogenation. J Solid State Chem 2008;181:2006e19. [42] Royer S, Duprez D, Kaliaguine S. Role of bulk and grain boundary oxygen mobility in the catalytic oxidation activity of LaCo1exFexO3. J Catal 2005;234:364e75. [43] Royer S, Alamdari H, Duprez D, Kaliaguine S. Oxygen storage capacity of La1xBO3 perovskites (with A0 ¼ Sr, Ce; B ¼ Co, Mn)drelation with catalytic activity in the CH4 oxidation reaction. Appl Catal B Environ 2005;58:273e88. [44] Guo JJ, Lou H, Zhu YH, Zheng XM. La-based perovskite precursors preparation and its catalytic activity for CO2 refonning of CH4. Mater Lett 2003;57:4450e5. ski J, Mista W, Zawadzki M. Ethanol [45] Białobok B, Trawczyn combustion over strontium- and cerium-doped LaCoO3 catalysts. Appl Catal B Environ 2007;72:395e403. [46] Brackmann R, Perez CA, Schmal M. LaCoO3 perovskite on ceramic monoliths - pre and post reaction analyzes of the partial oxidation of methane. Int J Hydrogen Energ 2014;39:13991e4007. [47] Scherrer B, Harvey AS, Tanasescu S, Teodorescu F, Botea A, Conder K, et al. Correlation between electrical properties and thermodynamic stability of ABO3-d perovskites (A¼ La, Pr, Nd, Sm, Gd). Phys Rev B 2011;84:085113. [48] Go KS, Son SR, Kim SD. Reaction kinetics of reduction and oxidation of metal oxides for hydrogen production. Int J Hydrogen Energ 2008;33:5986e95. [49] Zhang RD, Li PX, Liu N, Yue WR, Chen BH. Effect of hardtemplate residues of the nanocasted mesoporous LaFeO3 with extremely high surface areas on catalytic behaviors for methyl chloride oxidation. J Mater Chem A 2014;2:17329e40. [50] Zhang XJ, Li HJ, Li Y, Shen WJ. Structural properties and catalytic activity of Sr-Substituted LaFeO3 perovskite. Chin J Catal 2012;33:1109e14.

[51] Ciambelli P, Cimino S, De Rossi S, Faticanti M, Lisi L, Minelli G, et al. AMnO3 (A¼La, Nd, Sm) and Sm1xSrxMnO3 perovskites as combustion catalysts: structural, redox and catalytic properties. Appl Catal B Environ 2000;24:243e53. [52] Baker RT, Metcalfe IS. Activity and deactivation of La0.8Ca0.2Cr0.9X0.1O3 (X¼Ni, Co) in dry methane using temperature-programmed techniques. Appl Catal a-Gen 1995;126:319e32. [53] Yan AY, Liu B, Tu BF, Dong YL, Cheng MJ. A temperatureprogrammed-reduction study on La1-xSrxCrO3 and surfaceruthenium-modified Lal-xSrxCrO3. J Fuel Cell Sci Tech 2007;4:79e83. [54] Sauvet AL, Fouletier J, Gaillard F, Primet M. Surface properties and physicochemical characterizations of a new type of anode material, La1-xSrxCr1-yRuyO3-d, for a solid oxide fuel cell under methane at intermediate temperature. J Catal 2002;209:25e34. [55] Russo N, Fino D, Saracco G, Specchia V. Studies on the redox properties of chromite perovskite catalysts for soot combustion. J Catal 2005;229:459e69. [56] Zhu JJ, Rahuman MSMM, van Ommen JG, Lefferts L. Partial oxidation of methane to synthesis gas in a dual catalyst bed system combining irreducible oxide and metallic catalysts. Stud Surf Sci Catal 2004;147:205e10. [57] Grunwaldt JD, Kimmerle B, Baiker A, Boye P, Schroer CG, Glatzel P, et al. Catalysts at work: from integral to spatially resolved X-ray absorption spectroscopy. Catal Today 2009;145:267e78. [58] Kimmerle B, Grunwaldt J-D, Baiker A, Glatzel P, Boye P, Stephan S, et al. Visualizing a catalyst at work during the ignition of the catalytic partial oxidation of methane. J Phys Chem C 2009;113:3037e40. [59] Giroir-Fendler A, Alves-Fortunato M, Richard M, Wang C, Diaz JA, Gil S, et al. Synthesis of oxide supported LaMnO3 perovskites to enhance yields in toluene combustion. Appl Catal B-Environ 2016;180:29e37. [60] Okamoto Y, Nakano H, Imanaka T, Teranishi S. X-ray photoelectron spectroscopic studies of catalysts d supported cobalt catalysts d. B Chem Soc Jpn 1975;48:1163e8. [61] Nakamura T, Petzow G, Gauckler LJ. Stability of the perovskite phase LaBO3 (B ¼ V, Cr, Mn, Fe, Co, Ni) in reducing atmosphere I. Experimental results. Mater Res Bull 1979;14:649e59. [62] Calle-Vallejo F, Martı´nez JI, Garcı´a-Lastra JM, Mogensen M, Rossmeisl J. Trends in stability of perovskite oxides. Angew Chem Int Ed 2010;49:7699e701. [63] Chen JH, Shi WB, Li JH. Catalytic combustion of methane over cerium-doped cobalt chromite catalysts. Catal Today 2011;175:216e22. [64] Liu X, Su W, Lu Z, Liu J, Pei L, Liu W, et al. Mixed valence state and electrical conductivity of La1xSrxCrO3. J Alloy Compd 2000;305:21e3. [65] Rida K, Benabbas A, Bouremmad F, Pena MA, MartinezArias A. Surface properties and catalytic performance of La1xSrxCrO3 perovskite-type oxides for CO and C3H6 combustion. Catal Commun 2006;7:963e8. [66] Merkle R, Maier J. The significance of defect chemistry for the rate of gasesolid reactions: three examples. Top Catal 2006;38:141e5. [67] Mihai O, Chen D, Holmen A. Catalytic consequence of oxygen of lanthanum ferrite perovskite in chemical looping reforming of methane. Ind Eng Chem Res 2011;50:2613e21. € ger FA, Vink HJ. Relations between the concentrations of [68] Kro imperfections in crystalline solids. In: Frederick S, David T, editors. Solid state physics. Academic Press; 1956. p. 307e435. [69] Evdou A, Zaspalis V, Nalbandian L. La1xSrxMnO3-d perovskites as redox materials for the production of high purity hydrogen. Int J Hydrogen Energ 2008;33:5554e62.