Anjali Patel

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.

Synthesis and Crystal Structure of an Oxovanadium(IV) Complex with a Pyrazolone Ligand and Its Use as a Heterogeneous Catalyst for the Oxidation of Styrene under Mild Conditions

1-Phenyl-3-methyl-4-touloyl-5-pyrazolone (ligand) was synthesized and used to prepare an oxovanadium(IV) complex. The complex was characterized by single-crystal X-ray analysis and various spectroscopic techniques. The single-crystal X-ray analysis of the complex shows that the ligands are coordinated in a syn configuration to each other and create a distorted octahedral environment around the metal ion. A heterogeneous catalyst comprising an oxovanadium(IV) complex and hydrous zirconia was synthesized, characterized by various physicochemical techniques, and successfully used for the solvent-free oxidation of styrene. The influence of the reaction parameters (percent loading, molar ratio of the substrate to H(2)O(2), amount of catalyst, and reaction time) was studied. The catalyst was reused three times without any significant loss in the catalytic activity.

Tungstophosphoric acid supported onto hydrous zirconia: Physicochemical characterization and esterification of 1ℴ and 2ℴ alcohol

The Keggin type heteropolyacid, 12-tungstophosphoric acid (PW), was supported onto hydrous zirconia (Z) by impregnation method and designated as ZH3. The ZH3 was calcinated at 300°C and 500°C and designated as ZH33 and ZH35, respectively. The resulting materials were characterized by FTIR, diffuse reflectance spectroscopy (DRS), XRD, surface area measurement (BET method) and particle size distribution. The surface morphology was studied by scanning electron microscopy. The acidity of all materials was evaluated by carrying out chemisorption of ammonia and esterification of 1ℴ alcohol (n-butanol) with different acids like formic acid, acetic acid and propionic acid and 2ℴ alcohol (cyclohexanol, iso-butanol) with acetic acid. Above studies show the high dispersion of HPA in a non-crystalline form on the support as well as uniform distribution of particles of ZH3 which contains 30% 12-tungstophosphoric acid. It also shows that when ZH3 was calcinated at 500°C, it possesses highest acidity for both chemisorption of NH3 as well as esterification reactions.

Biodiesel synthesis via esterification and transesterification over a new heterogeneous catalyst comprising lacunary silicotungstate and MCM-41

Mono-vacant silicotungstate anchored to MCM-41 was synthesized by a direct post-synthesis grafting method and characterized by BET surface area measurements, FT-IR, 29Si MAS NMR, XRD and TEM. The catalytic application of the material was established for acid catalyzed synthesis of biodiesel via esterification of oleic acid and transesterification of different edible and non-edible oils such as waste cooking oil, jatropha oil, sunflower oil, cotton seed oil and mustard oil. A kinetic study was carried out for the esterification of oleic acid and it was found that esterification of oleic acid follows first order kinetics with the calculated activation energy Ea = 49.8 kJ mol−1 and pre-exponential factor A = 8.7 × 104 min−1. The expected mechanism for the biodiesel synthesis via esterification and transesterification has also been proposed.

Synthesis, structural, and spectral characterization of Keggin-type mono cobalt(II)-substituted phosphotungstate

Keggin-type mono Co(II)-substituted phosphotungstate was synthesized from 12-tungstophosphoric acid and cobalt chloride tetrahydrate. The obtained complex was systematically characterized in solution as well as solid by various physicochemical techniques. A single-crystal X-ray analysis shows that the complex crystallizes in tetragonal system, P42/ncm space group with a = b = 20.9860(5) Å, c = 10.4368(3) Å, and Z = 4. The crystal showed two types of disorders related by center of symmetry. Structural studies did not show the presence of Co, but the incorporation of the metal ion was proved by various spectral techniques. Spectral as well as electrochemical studies confirmed the presence of Co(II) into the lacunary position of the phosphotungstate moiety.

Keggin-type cesium salt of first series transition metal-substituted phosphomolybdates: one-pot easy synthesis, structural, and spectral analysis

The Keggin-type cesium salt of transition metal-substituted phosphomolybdates, Cs5[PCo(H2O)Mo11O39] · 6H2O (1) and Cs5[PMn(H2O)Mo11O39] · 6H2O (2), were synthesized from commercially available H3PMo12O40. The compounds were characterized by thermal, structural, and spectroscopic techniques. X-ray structural analysis reveals that, in these isostructural disordered compounds, the transition metal (Co/Mn) and Mo atoms are distributed over 12 positions. The presence of Co/Mn atoms was confirmed by powder XRD, FT-IR, DR-UV-Vis, ESR, and 31P NMR studies.

Room temperature acetalization of glycerol to cyclic acetals over anchored silicotungstates under solvent free conditions

Heterogeneous catalysts comprising of parent Keggin type silicotungstate as well as monolacunary silicotungstate anchored to MCM-41 were synthesized and characterized by several physicochemical methods. A solvent free green route towards valorisation of glycerol via acetalization with benzaldehyde has been proposed. Both the catalysts showed very good activity as well as selectivity towards dioxolane derivatives within a short reaction time and at room temperature. The tuning of the acidity of the parent silicotungstate leads to an increase in the selectivity towards 1,3-dioxolane. The catalysts were also recycled up to four times without any significant loss in the conversion. The excellent performance of these mesoporous catalysts is attributed to their combination of acidity, wide pores and large specific surface area.

Keggin type transition metal substituted phosphomolybdates: heterogeneous catalysts for selective aerobic oxidation of alcohols and alkenes under solvent free condition

Environmentally benign oxidation of alcohols and alkenes over transition metal substituted phosphomolybdates with molecular oxygen as an oxidant and TBHP as an initiator was carried out. The influence of different parameters on the conversion as well as the selectivity was investigated. All the catalysts showed good catalytic activity with excellent selectivity for the desired products as well as a higher TON. The system not only catalyzes the reaction but also avoids the use of organic solvents as it was carried out under solvent free conditions. Moreover, the catalysts could be recovered and reused four times without a significant loss in their activity and selectivity. A probable reaction mechanism was also proposed for the oxidation of alcohols and alkenes.

Heck coupling catalyzed by Pd exchanged supported 12-tunstophosphoric acid—an efficient ligand free, low Pd-loading heterogeneous catalyst

A stable, efficient ligand free, low Pd-loading heterogeneous catalyst comprising Palladium and supported 12-tunstophosphoric acid was synthesized and characterized by various physico-chemical techniques. The catalytic performance of this Pd-exchanged supported 12-tunstophosphoric acid was evaluated for the Heck coupling of olefins with halobenzene. A catalytic activity for recycled catalyst was also evaluated under optimized conditions. The results demonstrated that the catalyst was truly heterogeneous, stable and very active under the present reaction conditions, and could be reused up to three cycles without any significant leaching.

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.