Effect of MAF-6 Crystal Size on Its Physicochemical and Catalytic Properties in the Cycloaddition of CO2 to Propylene Oxide

Maria N. Timofeeva,Biswa Nath Bhadra,Ivan A. Lukoyanov,Evgenii Yu Gerasimov,Sung Hwa Jhung,Valentina N. Panchenko

doi:10.3390/catal11091061

Abstract

Zeolitic imidazolate frameworks MAF-5 and MAF-6 based on Zn2+ and 2-ethylimidazole were demonstrated to be efficient heterogeneous catalysts in solvent-free coupling of CO2 and propylene oxide (PO) to produce propylene carbonate (PC) at 0.8 MPa of CO2 and 80 °C. Activity of MAF-5 was lower in comparison with MAF-6 due to the difference in their structural and textural characteristics. MAF-6 samples with particle size of 190 ± 20, 360 ± 30, and 810 ± 30 nm were prepared at room temperature from [Zn(NH3)4](OH)2 and 2-ethylimidazole. Control of particle size was achieved by variation of type of alcohol in alcohol/cyclohexane media for the preparation of MAF-6. According to this comprehensive study, the yield of PC was found to decrease with increasing crystal size of the MAF-6 material, which was related to the change in textural properties and the number and localization of active sites. The combination of MAF-6 with particle size of with particle size of 190 ± 20 nm and tetrabutylammonium bromide ([n-Bu4N]Br) as co-catalyst led to an approximately 4-fold enhancement in the yield of PC (80.5%). Compared with reported ZIFs catalysts, the efficiencies of MAF-5/[n-Bu4N]Br and MAF-6/[n-Bu4N]Br binary systems were comparable and higher under similar reaction conditions.

Highlights

Nowadays, it nearly impossible to imagine modern life without the products of chemistry
We have recently studied the effect of Zeolitic imidazolate frameworks (ZIFs)-8 particle size (50–800 nm) in a hexagonal shape on their catalytic efficiency in the synthesis of propylene glycol methyl ether (PGME)
The experimental data (Table 3) show the particle size of MAF-6 decreases in the following order, because of solvent effect: MAF-6(L) (MeOH) > MAF-6(M) (EtOH) > MAF-6(S) (PrOH)

Summary

Introduction

It nearly impossible to imagine modern life without the products of chemistry. The chemicals industry and other related industries supply us with a huge variety of essential products, from plastics to pharmaceuticals. These industries are based on the utilization of fossil fuels as a source of energy and feedstocks, and often release pollutants into the environment that provokes both economic and environmental challenges. To use renewable carbon resources, i.e., biomass and CO2 , in the chemical and energy industries, it is a key to finding lasting solutions to both economic and environmental challenges. CO2 represents a potential and alternative carbon feedstock for the preparation of a variety of useful chemicals [1,2,3,4].

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