Sukriti Singh

Recent progress on supported polyoxometalates for biodiesel synthesis via esterification and transesterification

Biodiesel is now recognized as a “green fuel” that has several advantages over conventional diesel. In the present review we discuss the catalytic esterification and transesterification reactions to the clean synthesis of biodiesel, over most readily investigated supported polyoxometalates to meet future societal demands. Here for the first time, we are reviewing biodiesel synthesis using supported lacunary polyoxometalates; also how the prevailing reaction conditions like reaction time, alcohol content, temperature, and catalyst amount affect the catalytic activity of the catalyst is discussed in detail. The new results for supported lacunary polyoxometalates are included where the effect of catalysts and supports was correlated with the catalytic activity.

Keggin-type lacunary and transition metal substituted polyoxometalates as heterogeneous catalysts: A recent progress

ABSTRACT In this article we discussed synthesis and catalytic applications of heterogeneous catalysts based on lacunary polyoxometalates (LPOMs) and transition metal substituted polyoxometalates (TMSPOMs), however exclusively the focus has been given to the mono LPOMs and mono-TMSPOMs. As the field of supported LPOMs/TMSPOMs is upcoming important field, some aspects about choice of support as well as methods of supporting have also been described. We also include a few of our new research results in order to understand the effect of support and active species as well as choice of organic transformation.

Oxidative Esterification of Aldehydes to Esters over Anchored Phosphotungstates

Abstract12-Tungstophosphoric acid and lacunary phosphotungstate anchored to MCM-41 and ZrO2 were synthesized, characterized and used as bifunctional catalyst for oxidative esterification of benzaldehyde with methanol. The different aldehyde substrates study show excellent selectivity for esters, indicating the scope of the catalysts. A tentative reaction mechanism for oxidative esterification of aldehyde is also proposed.Graphical Abstract

Aerobic oxidation of alcohols and alkenes over a novel lacunary phosphomolybdate anchored to zeolite Hβ

Lacunary phosphomolybdate anchored to zeolite Hβ was synthesized and characterised by various physicochemical techniques. The catalytic activity was evaluated for aerobic oxidation of benzyl alcohol and styrene. The catalyst was found to be efficient, especially in terms of selectivity for the desired benzaldehyde product (for benzyl alcohol – 90%, styrene – 72%), very high turnover number (alcohols > 3500, alkenes > 18 000) as well as recyclability. The viability of the catalyst was also extended to various alkenes and alcohols.

Environmentally Benign Oxidations of Alkenes and Alcohols to Corresponding Aldehydes over Anchored Phosphotungstates: Effect of Supports as Well as Oxidants

Series of catalysts comprising of parent phosphotungstate (PW12) and mono lacunary phosphotungstate (PW11) anchored to different mesoporous materials (MCM-41 and MCM-48) were prepared. Environmentally benign oxidation of alkenes and alcohols were carried out with H2O2 and molecular oxygen as oxidants. The influence of different parameters on the conversion as well as the selectivity was investigated. Comparative study was ascertained over anchored parent, lacunary phosphotungstates as active species and the supports. The kinetic and thermodynamic studies were correlated with the effect of support as well as active species. Moreover, the catalysts could be recovered and reused four times without significant loss in their activity and selectivity.Graphical Abstract

Value added products derived from biodiesel waste glycerol: activity, selectivity, kinetic and thermodynamic evaluation over anchored lacunary phosphotungstates

New prospects for conversion of glycerol into value-added products was explored by choosing viable reaction conditions with Lacunary phosphotungstate anchored to mesoporous (MCM-41, MCM-48) as catalysts. Both the catalysts showed high conversion for glycerol esterification as well as oxidation with higher selectivity towards di-acetyl glycerol and dihydroxyacetone products, respectively. The kinetic studies shows that both the catalysts are thermodynamically and kinetically stable, having first order dependence with no mass transfer limitation. The difference in % conversion and selectivity was correlated with the nature of supports, where the three dimensional pore network of MCM-48 resulted in better activity. Multiple use of catalyst suggested regeneration without significant loss in the activity. Probable mechanism was also demonstrated for both the reactions.