Acid Modified H-USY Zeolite for Efficient Catalytic Transformation of

Article Cite This: Energy Fuels 2018, 32, 3783−3791

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Acid Modified H‑USY Zeolite for Efficient Catalytic Transformation of Fructose to 5‑Hydroxymethyl Furfural (Biofuel Precursor) in Methyl Isobutyl Ketone−Water Biphasic System Ashwini Pande,† Prashant Niphadkar,† Kiran Pandare,‡ and Vijay Bokade*,† †

Catalysis Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pashan, Pune 411008, India Polymer Science and Engineering, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pashan, Pune, Maharashtra 411008, India

‡

ABSTRACT: Sustainable process and efficient heterogeneous acid catalyst for the preparation of platform chemicals like 5hydroxymethyl furfural (5-HMF) from renewable source is much in demand in the context of heterogeneous catalysis. Commercially available solid acid catalyst, H-USY zeolite was modified by treating with aqueous solution of H3PO4 and H2SO4 (10−30 wt %). Modified H-USY was completely characterized by XRD, NH3-TPD, energy dispersive analysis X-ray (EDAX), FT-IR, pyridine-IR, and NMR. Its catalytic performance was evaluated for the fructose conversion to 5-HMF in methyl isobutyl ketone (MIBK)−water system. Modified H-USY zeolite was identified to have potential in enhancement of 5-HMF yield up to 65% from 32% (parent H-USY) with minimum formation of furfural (8%). H-USY modified with 10 wt % H3PO4 (10P−Y) was found to be the best compared to other studied catalysts, namely, H-USY modified with 20 and 30 wt % H3PO4 (20 and 30P−Y) or 10−30 wt % H2SO4 (10- to 30S−Y). Best performance of 10P−Y is associated with the optimum combination of moderate acidity (both weak as well as strong), moderate dealumination of Al from extra-framework sites as well as from framework sites of H-USY, formation of new Al−O−P bonds between framework Al and elemental monomeric phosphorus, presence of Brønsted as well as Lewis acidity, and creation of mesopores. This gives new insight on a potential heterogeneous acid catalyst for the synthesis of 5-HMF.

1. INTRODUCTION Due to long-term sustainability issues of fossil fuel resources, it is necessary to apply renewable biomass sources to energy, chemical, and alternative fuels production.1,2 In the Indian context, as per TIFAC (Technology Information Forecasting & Assessment Council) 2014 report of the Government of India, almost 623.4 million metric tons per year of biomass waste is generated of which 70% is contributed from agricultural waste, such as rice husk, wheat and rice straw, and sugar cane baggasse. In general, such biomass contains mainly C6 sugar, and its contribution is in the range of 33−51% based on the biomass source.1 Thus, converting this major compound of C6 sugar, such as cellulose, glucose, and fructose, to valuable chemicals is an industrially and academically attractive option.3 Cellulose and glucose can be easily converted to fructose by acid hydrolysis and isomerization, respectively.4,5 Further efficient conversion of fructose to desired chemicals using the right choice of heterogeneous catalyst is challenging and needs more research and development to make the catalytic process benign and industrially relevant. Among various reactions of fructose conversion, efficient transformation of fructose to 5hydroxymethyl furfural (5-HMF) is an important reaction to explore to identify a new, stable, economical, and reusable, easily available heterogeneous catalyst. This type of catalyst is superior compared to homogeneous catalysts due to environmental issues.6,7 As per the US-DOE, 5-HMF is documented among the 14 top biobased chemicals, having wide application for the synthesis of chemicals, such as levulinic acid, bioethanol, alkoxymethylfurfurals, or hydroxymethylfuran.8 5-HMF is still a topic of interest due to the need for a less selective and costly © 2018 American Chemical Society

process. The stability of 5-HMF can be improved in reactions by using suitable extracting solvents like dimethyl sulfoxide (DMSO), methyl isobutyl ketone (MIBK), and MIBK−water biphasic system. Among these solvents, the MIBK−water biphasic system was reported to be the best solvent system, improving activity especially for fructose dehydration to 5HMF.6,7,9 Various acidic heterogeneous catalysts, such as Al, Al−Si, Zr phosphate,10 niobic acid,11 ion-exchange resins,12,13 and zeolites14 like mordinite, H-β, H-ZSM-5, and H−Y, have been reported. Among these catalysts, zeolites seem to be the best potential option due to their thermal stability, porous structure, adjustable acidity, commercial availability, and reusability associated with catalytic performance. Based on the available reported literature, H-USY zeolite and its modified versions having additional features of mesoporosity as a catalyst have not been explored for fructose dehydration to 5-HMF so far. H-USY zeolite is used in chemical processes and is an ultrastable form of Y zeolite.15,16 The activity of H-USY can be tuned by altering its acidity. To modify the acidity of H-USY, it is necessary to modify the catalyst during synthesis or by postsynthesis treatment. A dealumination of zeolite, removing Al atoms from the lattice, is one of the best postsynthesis treatments to alter the acidity. Dealumination can be carried out by different methods.17 Modifed H-USY zeolites make changes in the Si/Al molar ratio of the framework, acidity, and porosity, enhancing catalytic activity for industrial relevance.18 Received: November 24, 2017 Revised: February 6, 2018 Published: February 7, 2018 3783

DOI: 10.1021/acs.energyfuels.7b03684 Energy Fuels 2018, 32, 3783−3791

Article

Energy & Fuels

run, fructose (1 g), catalyst (1 g), and 50 mL of MIBK−water mixture (MIBK/water volume ratio of 10:1, that is, 45.5 mL of MIBK and 4.5 mL of water) were placed in the autoclave. The reaction was conducted in the temperature range of 100−140 °C for 5 h at 600 rpm. As per the open domain,11,33,34 external diffusion does not interfere with the overall rate of reaction unless stirrer speed is very low (