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The present review is focused on a recent development in the preparation of various layered hydrotalcites and their applications in environmental, catalytic and supported materials.

Lignocellulosic material (LCM) has been considered as a potent feedstock for biofuel production either as gaseous, liquid, and/or solid fuel to meet the energy demands. Conversion of lignocellulosic materials to biofuels is possible mainly by two processes, i.e., thermochemical and biochemical. For overall efficiency of processes designed to convert the lignocellulosic materials into the desired biofuel, it is important to understand the characteristics of these lignocellulosic components. The present study aims for physicochemical characterization of common lignocellulosic agricultural residues available in India, i.e., rice straw, rice husk, cotton stalk, wheat straw, bagasse, corn stover, sorghum stalk, mustard stalk, corn cob, and jatropha pruning. Physical and chemical characterization of lignocellulosic samples is carried out by higher heating value, crystallinity index, thermal properties, CHNS/O analysis, FTIR, metal analysis, and compositional analysis. Among all of the biomass samples analyzed, corn cob has the highest content of cellulose and hemicellulose, i.e., 61.2% (w/w), making it the most potent feedstock for production of biofuels using biochemical process, whereas cotton stalk has relatively higher thermochemical potential due to its higher heating value (19.2 MJ/kg). Rice husk and rice straw have the highest ash content, i.e., 17.4 and 13.7% (w/w), respectively, indicating a significant amount of undesirable material.

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Rhodium containing macromolecules calix[4]pyrrole (RhCP) and tetraphenyl porphyrin (RhTPP) were prepared and grafted on the surface of functionalised molecular sieve materials. 1H and 13C NMR, CHNS and mass spectral analyses were used for the structural elucidation of homogeneous organometallic complexes.1H NMR and CHNS analyses confirm the formation of calix[4]pyrrole (CP) and tetraphenyl porphyrin (TPP). The introduction of rhodium ions into the macromolecule is well evident from the disappearance of the 1H NMR signal characteristic of N-H proton (7.1 ppm in CP and -2.74 ppm in TPP). Furthermore the formation of RhCP and RhTPP complexes is confirmed using CHNS and mass spectral analysis; the data are in line with theoretically calculated values. The grafting of RhCP and RhTPP on a diamino functionalised SBA-15 support was confirmed through low angle XRD, 13C MAS-NMR and SEM-EDAX analysis. Both homogeneous and heterogeneous catalysts were utilized for nitrobenzene reduction. RhCP and RhTPP heterogenized on SBA-15-F showed complete conversion of nitrobenzene with exclusive formation of aniline as a product. The catalytic activities were retained in both the systems even after several runs.

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Silicate intercalated CoAl hydrotalcite materials were synthesized (CoAl-HT-Si) and systematically characterized. The intercalated hydrotalcite materials lead to the formation of solid solutions of cobalt silicate and cobalt spinel structures, which have higher surface area and pore volume than pure CoAl-HT. The XPS studies revealed the presence of cobalt in divalent and trivalent oxidation states on the surface. The resultant materials were found to be promising catalysts for oxidation of various alcohols. Experimental sectionHydrotalcite (HT) with a Co-Al molar ratio 3 : 1 was synthesized according to a method previously described in the literature. 24 Scheme 1 Schematic representation of intercalation on HT.