Rawesh Kumar

Sn-ZSM-12, a new, large pore MTW type tin-silicate molecular sieve: synthesis, characterization and catalytic properties in oxidation reactions

A new large pore tin-silicate analogue of zeolite ZSM-12 (MTW topology) with Si/Sn molar ratio >70 has been synthesized hydrothermally using a new template, hexamethylene bis(benzyl dimethyl ammonium hydroxide). This material exhibits an expansion in unit cell volume (XRD), an IR band at 970 cm−1 and a charge transfer band at 205 nm in the UV-Vis region indicating the presence of Si-O-Sn units with Sn4+ centers in Td configuration. Sn-ZSM-12 catalyzes the oxidation of phenol,m-cresol andm-xylene using dilute H2O2 as an oxidizing agent.

Niobium doped hexagonal mesoporous silica (HMS-X) catalyst for vapor phase Beckmann rearrangement reaction

The synthesis of e-caprolactam, a demanding monomer, through a heterogeneous catalytic pathway has remained a key area of research in the last decade. The Beckmann rearrangement reaction in the vapor phase using a solid acid catalyst was found to be very effective for producing e-caprolactam. It is observed that niobium incorporated into mesoporous silica serves as a good catalyst for the Beckmann rearrangement reaction. Recently developed mesoporous silica, having an ordered honeycomb structure, is very useful as it can lead to effective diffusion of reactants and products for several reactions. In this study, Nb-doped mesoporous HMS-X nanocomposite materials with different Nb loadings were prepared by a one step hydrothermal synthesis and characterized by BET surface area and porosity measurements, wide and small angle XRD, SEM, HR-TEM, elemental mapping, FTIR, 29Si-NMR and NH3-TPD techniques. The activity of the Nb–HMS-X catalyst was evaluated for the vapour phase Beckmann rearrangement reaction. The catalyst characterization study shows that Nb is highly dispersed on the HMS-X matrix at lower Nb loadings. At higher Nb loadings it is present in the extra-framework position as revealed from XRD, HR-TEM and 29Si-NMR studies. The NH3-TPD result shows the presence of acidic sites on the catalyst surface, which are active sites for the Beckmann rearrangement reaction. Using the Nb–HMS-X catalyst (Si/Nb = 13) under vapour-phase reaction conditions [temperature = 350 °C, weight hourly space velocity (WHSV) = 15 h−1, cyclohexanone oxime in benzene, cyclohexanone oxime : benzene weight ratio of 1 : 11] gave 100% cyclohexanone oxime conversion with 100% e-caprolactam selectivity, with a space time yield of 1.4–1.6 × 10−3 mol h−1 gcat−1. The catalyst was highly recyclable up to 9 times without significant loss of catalytic activity.

Mesoporous TUD-1 supported indium oxide nanoparticles for epoxidation of styrene using molecular O2

Activation of molecular O2 by metal or metal oxide nanoparticles is an area of recent research interest. In this work, for the first time, we report that indium oxide nanoparticles of <3 nm size dispersed on mesoporous silica (TUD-1) can activate molecular O2 and produce styrene epoxide with a selectivity of 60% and styrene conversion around 25% under mild conditions. It is found that neither indium oxide nor TUD-1 themselves respond to the styrene epoxidation reaction. The computational studies provide evidence that an oxygen molecule is highly polarized when it is located near the interface of both surfaces. The kinetic study shows that the reaction is of pseudo-first order and that the activation energy for styrene conversion is 12.138 kJ mol−1. The catalysts are recyclable for up to four regeneration steps, with the styrene conversion and styrene epoxide selectivity almost unchanged.