[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Recent Advances in Polyoxometalate-Catalyzed Reactions

Novel catalytic materials are highly demanded to perform a variety of catalytic organic reactions. MOFs combine the benefits of heterogeneous catalysis like easy post reaction separation, catalyst reusability, high stability and homogeneous catalysis such as high efficiency, selectivity, controllability and mild reaction conditions. The possible organization of active centers like metallic nodes, organic linkers, and their chemical synthetic functionalization on the nanoscale shows potential to build up MOFs particularly modified for catalytic challenges. In this review, we have summarized the recent research progress in heterogeneous catalysis by MOFs and their catalytic behavior in various organic reactions, highlighting the key features of MOFs as catalysts based on the active sites in the framework. Examples of their post functionalization, inclusion of active guest species and metal nanoparticles have been discussed. Finally, the use of MOFs as catalysts for asymmetric heterogeneous catalysis and stability of MOFs has been presented as separate sections.

Metal–organic frameworks: versatile heterogeneous catalysts for efficient catalytic organic transformations

Concern over the economics of accessing fossil fuel reserves, and widespread acceptance of the anthropogenic origin of rising CO2 emissions and associated climate change from combusting such carbon sources, is driving academic and commercial research into new routes to sustainable fuels to meet the demands of a rapidly rising global population. Here we discuss catalytic esterification and transesterification solutions to the clean synthesis of biodiesel, the most readily implemented and low cost, alternative source of transportation fuels to meet future societal demands.

/pdf/heterogeneous-catalysis-for-sustainable-biodiesel-production-wruq11o683.pdf

Heterogeneous catalysis for sustainable biodiesel production via esterification and transesterification

Two novel polyoxometalate (POM)-based metal–organic frameworks (MOFs), [TBA]3[e-PMoV8MoVI4O36(OH)4Zn4][BTB]4/3·xGuest (NENU-500, BTB = benzene tribenzoate, TBA+ = tetrabutylammonium ion) and [TBA]3[e-PMoV8MoVI4O37(OH)3Zn4][BPT] (NENU-501, BPT = [1,1′-biphenyl]-3,4′,5-tricarboxylate), were isolated. In these compounds, the POM fragments serving as nodes were directly connected with organic ligands giving rise to three-dimensional (3D) open frameworks. The two anionic frameworks were balanced by TBA+ ions residing inside the open channels. They exhibit not only good stability in air but also tolerance to acidic and basic media. Furthermore, they were employed as electrocatalysts for the hydrogen evolution reaction (HER) owing to the combination of the redox activity of a POM unit and the porosity of a MOF. Meanwhile, the HER activities of e(trim)4/3, NENU-5, and HKUST-1 were also studied for comparison. Remarkably, as a 3D hydrogen-evolving cathode operating in acidic electrolytes, NENU-500 exhibits the hig...

Ultrastable Polymolybdate-Based Metal–Organic Frameworks as Highly Active Electrocatalysts for Hydrogen Generation from Water

12-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.

Oxidative Esterification of Aldehydes to Esters over Anchored Phosphotungstates

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.

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

This chapter gives an overview of the work carried out in our group on the application of various forms of heteropoly acids (HPAs) for ammoxidation of methylpyrazine (MP). It starts with a general description of HPAs, ammonium salts of HPA, and the metal substituted HPAs (combinedly called as heteropoly compounds, HPCs). The various methods adopted for the synthesis of these compounds have been described. The HPCs have also been dispersed on different supports, and the methodology of their preparation is presented. Different characterization techniques have been used to determine their physicochemical properties. The reactivity of the catalysts is evaluated for the ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyrazine (CP). The enhanced thermal stability and activity of the supported systems compared with those of the bulk ones are highlighted. Two new methods – one for the preparation of catalysts by in situ synthesis of the ammonium salt of heteropoly acid on supports and the other for the determination of dispersion of HPC on the support by FTIR technique – developed in our laboratory are introduced. Finally, correlations drawn between the activity and selectivity with the physicochemical properties of HPCs are presented.

Environmentally Benign Catalysts

An ecofriendly solid catalytic system comprising undecaphosphotungstate and neutral alumina was found to be an efficient catalytic system for solvent-free liquid-phase aerobic epoxidation of alkenes under mild reaction conditions. The superiority of the present catalyst lies in achieving 85% conversion for cyclohexene with 100% selectivity toward cyclohexene oxide. Further, the catalyst can be regenerated and can be reused up to three cycles without any significant loss in the catalytic activity.

Supported Undecaphosphotungstate: An Ecofriendly and Efficient Solid Catalyst for Nonsolvent Liquid-Phase Aerobic Epoxidation of Alkenes

The catalytic conversion of bio-platform molecules into desired products can be an important unit for the future biorefinery. The present contribution consists of synthesis of solid acid catalyst comprising 20 % 12-tungstophosphoric acid (TPA) and MCM-41 and its characterization by various physico-chemical techniques such as fourier transform infrared, X-ray diffraction surface area measurement (BET method), transmission electron microscopy and total acidity. The use of synthesized catalyst was explored for esterification of bio-platform molecules such as succinic acid and malonic acid with different alcohols. The catalyst shows high activity in terms of higher yields towards all diesters. The product selectivity towards the mono and diester was found to be the same for TPA alone and supported system, TPA2/MCM-41, that also confirms the uniform distribution of the TPA on MCM-41. The excellent catalytic performance is attributed to the large surface area and pore diameter of the mesoporous support, MCM-41 as well as the Bronsted acid strength of TPA, as active sites. The catalyst shows the potential of being used as a recyclable catalytic material after simple regeneration without significant loss in activity.

Anjali Patel

Papers

Oxidative Esterification of Aldehydes to Esters over Anchored Phosphotungstates

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

Environmentally Benign Catalysts

Supported Undecaphosphotungstate: An Ecofriendly and Efficient Solid Catalyst for Nonsolvent Liquid-Phase Aerobic Epoxidation of Alkenes

Esterification of bioplatform molecules over 12-tungstophosphoric acid anchored to MCM-41