Sudipta De

Advances in conversion of hemicellulosic biomass to furfural and upgrading to biofuels

Recent approaches to furfural synthesis from hemicellulosic biomass and pentose sugars with both homogeneous and solid acidic catalysts have been summarized by addressing the associated sustainability issues. The features of deconstruction of hemicellulosic biomass by acid hydrolysis to produce pentose sugar feedstock for furfural have been discussed in brief. Several strategies including solvent extraction in a biphasic process, application of surface functionalized materials such as acidic resins, mesoporous solids and mechanistic insight in limited cases are discussed. The present status of the promising furfural platform in producing second generation biofuels (furanics and hydrocarbon) is reviewed. The performances of each catalytic system are assessed in terms of intrinsic reactivity and selectivity toward furfural production. Overall, this minireview attempts to highlight the scope of further developments for a sustainable furfural process and upgrading to fuels.

Microwave assisted conversion of carbohydrates and biopolymers to 5-hydroxymethylfurfural with aluminium chloride catalyst in water

The common Lewis acid AlCl3 has efficiently produced 5-hydroxymethylfurfural (HMF) from carbohydrate and biopolymer substrates in water, DMSO, and water–methylisobutylketone biphasic solvents under microwave irradiation. The yield of HMF in different solvents follows an increasing order from water to water–MIBK biphasic solvent to DMSO. The yield of HMF increased with an increase in catalyst loading whereas it remains unchanged upon increase of the carbohydrate concentration. In most reactions, the maximum yield of HMF is recorded within 2 min of reaction time. The mechanism of the AlCl3 catalyzed glucose dehydration reaction is proposed to proceed through the isomerization of glucopyranose to fructofuranose, followed by a proton assisted transformation of fructofuranose to HMF.

Hydrodeoxygenation processes: advances on catalytic transformations of biomass-derived platform chemicals into hydrocarbon fuels.

Lignocellulosic biomass provides an attractive source of renewable carbon that can be sustainably converted into chemicals and fuels. Hydrodeoxygenation (HDO) processes have recently received considerable attention to upgrade biomass-derived feedstocks into liquid transportation fuels. The selection and design of HDO catalysts plays an important role to determine the success of the process. This review has been aimed to emphasize recent developments on HDO catalysts in effective transformations of biomass-derived platform molecules into hydrocarbon fuels with reduced oxygen content and improved H/C ratios. Liquid hydrocarbon fuels can be obtained by combining oxygen removal processes (e.g. dehydration, hydrogenation, hydrogenolysis, decarbonylation etc.) as well as by increasing the molecular weight via C-C coupling reactions (e.g. aldol condensation, ketonization, oligomerization, hydroxyalkylation etc.). Fundamentals and mechanistic aspects of the use of HDO catalysts in deoxygenation reactions will also be discussed.

Ni-based bimetallic heterogeneous catalysts for energy and environmental applications

Bimetallic catalysts have attracted extensive attention for a wide range of applications in energy production and environmental remediation due to their tunable chemical/physical properties. These properties are mainly governed by a number of parameters such as compositions of the bimetallic systems, their preparation method, and their morphostructure. In this regard, numerous efforts have been made to develop “designer” bimetallic catalysts with specific nanostructures and surface properties as a result of recent advances in the area of materials chemistry. The present review highlights a detailed overview of the development of nickel-based bimetallic catalysts for energy and environmental applications. Starting from a materials science perspective in order to obtain controlled morphologies and surface properties, with a focus on the fundamental understanding of these bimetallic systems to make a correlation with their catalytic behaviors, a detailed account is provided on the utilization of these systems in the catalytic reactions related to energy production and environmental remediation. We include the entire library of nickel-based bimetallic catalysts for both chemical and electrochemical processes such as catalytic reforming, dehydrogenation, hydrogenation, electrocatalysis and many other reactions.

Stabilizing a Platinum1 Single‐Atom Catalyst on Supported Phosphomolybdic Acid without Compromising Hydrogenation Activity

In coordination chemistry, catalytically active metal complexes in a zero- or low-valent state often adopt four-coordinate square-planar or tetrahedral geometry. By applying this principle, we have developed a stable Pt1 single-atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)-modified active carbon. This was achieved by anchoring Pt on the four-fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square-planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities.

One‐Pot Conversions of Lignocellulosic and Algal Biomass into Liquid Fuels

The one-pot conversion of lignocellulosic and algal biomass into a liquid fuel, 2,5-dimethylfuran (DMF), has been achieved by using a multicomponent catalytic system comprising [DMA]⁺ [CH₃SO₃]⁻ (DMA=N,N-dimethylacetamide), Ru/C, and formic acid. The synthesis of DMF from all substrates was carried out under mild reaction conditions. The reaction progressed via 5-hydroxyemthylfurfural (HMF) in the first step followed by hydrogenation and hydrogenolysis of HMF with the Ru/C catalyst and formic acid as a hydrogen source. This report discloses the effectiveness of the Ru/C catalyst for the first time for DMF synthesis from inexpensive and readily abundant biomass sources, which gives a maximum yield of 32 % DMF in 1 h. A reaction route involving 5-(formyloxymethyl)furfural (FMF) as an intermediate has been elucidated based on the ¹H and ¹³C NMR spectroscopic data. Another promising biofuel, 5-ethoxymethylfurfural (EMF), was also synthesized with high selectivity from polymeric carbohydrate-rich biomass substrates by using a Brønsted acidic ionic liquid catalyst, that is [DMA]⁺ [CH₃SO₃]⁻, by etherification of HMF in ethanol.

Self-assembly of mesoporous TiO2 nanospheres viaaspartic acid templating pathway and its catalytic application for 5-hydroxymethyl-furfural synthesis

Self-assembled mesoporous TiO2 nanoparticulate material with well-defined nanospherical morphologies was prepared by using DL-aspartic acid as a template. Powder XRD, TEM and SEM techniques were used to characterize the TiO2 nanoparticles. The presence of high acid density in the mesoporous TiO2 was confirmed by pyridine-IR and NH3-TPD studies. This new mesoporous TiO2 nanomaterial efficiently catalyzed the dehydration of D-fructose and D-glucose into 5-hydroxymethylfurfural in DMA-LiCl solvent under microwave assisted heating. The acidic sites of the TiO2 nanomaterial were responsible for the dehydration reaction which produced a maximum 82.3% HMF.

Biomass‐Derived Porous Carbon Materials: Synthesis and Catalytic Applications

Novel biomass‐derived porous carbons are attractive candidates for the preparation of carbon‐supported catalysts with a wide range of catalytic applications. Such carbonaceous catalysts are environmentally benign and could provide a cost‐competitive advantage as compared to existing heterogeneous catalysts. Tunable surface properties of carbon materials and excellent physical properties (e.g., hydrophobicity, chemically inert nature, etc.) are compatible with diverse catalysis reactions including organic transformations, as well as electro‐ and photochemical processes in aqueous solutions. This contribution provides an overview on the utilization of different biomass feedstocks and/or biomass‐derived precursors for the synthesis of carbonaceous materials to design advanced catalytic systems and their emerging applications in catalysis.

Solid-acid and ionic-liquid catalyzed one-pot transformation of biorenewable substrates into a platform chemical and a promising biofuel

A wide variety of polymeric carbohydrate-rich weed species were directly converted to a platform chemical, 5-hydroxymethylfurfural (HMF), and a promising next-generation biofuel, 5-ethoxymethyl-2-furfural (EMF), with homogeneous and heterogeneous catalysts under mild reaction conditions. Bronsted acidic IL catalysts, [DMA]+[CH3SO3]− and [NMP]+[CH3SO3]−, were found to be effective enabling maximum 58 and 52 wt% HMF yields, respectively, from foxtail weed. Strong Lewis acidic silica supported heteropolyacid (HPA-SiO2) catalyst was also effective producing a maximum 32 wt% HMF from the same weed substrate. Both IL catalysts were effective for high-purity EMF production from HMF and weeds. HMF was quantitatively converted to EMF in 2 h. In the case of weed substrates, EMF was formed as the major product. The ratio of EMF and ethyl levulinate (EL) in the isolated product was 7 : 1. To address the sustainability issue and potential industrial application opportunity of the current method, a larger scale experiment under conventional heating demonstrated to produce 55 wt% HMF in 4 h. Most importantly, the spent catalyst and the solvent system were efficiently recycled for four consecutive catalytic cycles without a significant loss in yield.

Self-Assembled TiO2 Nanospheres By Using a Biopolymer as a Template and Its Optoelectronic Application

Self-assembled TiO(2) nanoparticulate materials with well-defined spherical morphologies were synthesized by using a biopolymer sodium alginate as a template under different synthesis conditions. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) techniques were used to characterize the TiO(2) nanoparticles. N(2) sorption analysis revealed the moderately good surface area (124.0 m(2) g(-1)) and pore volume (0.44 cm(3) g(-1)) of these TiO(2) nanoparticles. The biopolymer templating pathway leads to good-quality self-assembled TiO(2) nanoparticles with dimensions of ca. 10-12 nm within the synthesis temperature range of 0-60 °C. These porous TiO(2) nanomaterials showed high photogenerated current in the presence of a dye (Rose Bengal), used as a sensitizer for several photo on/off cycles.