Effect of Calcination Atmosphere and Temperature on the Hydrogenolysis Activity and Selectivity of Copper-Zinc Catalysts

Oleg Kikhtyanin,Jaroslav Aubrecht,David Kubička,Miloslav Lhotka,Violetta Pospelova

doi:10.3390/catal8100446

Oleg Kikhtyanin, Jaroslav Aubrecht + Show 3 more

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https://doi.org/10.3390/catal8100446

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Abstract

A series of CuZn catalysts with a Cu/Zn ratio of 1.6 was prepared by the calcination of a single precursor, CuZn-P consisting of an equimolar mixture of aurichalcite and zincian malachite, in three different calcination atmospheres (air, nitrogen, and hydrogen) at three temperatures (220, 350, and 500 °C). All catalysts were characterized by XRD and N2-physisorption to assess their phase composition, crystallite sizes and textural properties and tested in dimethyl adipate (DMA) hydrogenolysis in a batch reactor at 220 °C and 10 MPa H2. The XRD examination of these catalysts proved that both parameters, calcination temperature and atmosphere, affected the resulting phase composition of the catalysts as well as their crystallite sizes. In an oxidizing atmosphere, CuO and ZnO in intimate contact prevailed whereas in inert or reducing atmosphere both oxides were accompanied by Cu2O and Cu. The crystallite size of Cu2O and Cu was larger than the size of CuO and ZnO thus indicating a less intimate contact between the Cu-phases and ZnO in catalysts calcined in nitrogen and hydrogen. Catalysts prepared by calcination at 220 °C and CuZn catalyst calcined in the air at 350 °C significantly outperformed the other catalysts in DMA hydrogenolysis with a 59–78% conversion due to the small crystallite size and intimate contact between the CuO and ZnO phases prior to catalyst reduction. Despite the low DMA conversion (<30%), transesterification products were the main reaction products with overall selectivities of >80% over the catalysts calcined in nitrogen or hydrogen at least at 350 °C. The obvious change in the preferred reaction pathway because of the atmosphere calcination and temperature shows that there are different active sites responsible for hydrogenolysis and transesterification and that their relative distribution has changed.

Highlights

Over the past few decades, increasing attention has been paid to green chemistry principles to achieve a higher sustainability of chemical technologies
The results from the present study show that starting from the same CuZn hydroxycarbonate precursor, it is possible to prepare samples greatly varying in physicochemical properties and catalytic performance
All three catalysts calcined in different atmospheres at T = 220 ◦ C demonstrated good activity, resulting in a dimethyl adipate (DMA) conversion of 59–63%

Summary

Introduction

Over the past few decades, increasing attention has been paid to green chemistry principles to achieve a higher sustainability of chemical technologies One of these principles is based on the application of highly efficient catalysts in industrial processes. Their efficiency alone does not guarantee the overall technological sustainability as some catalyst productions use or produce harmful materials. Have been2018, used industrial copper-zinc catalysts have been shown to possess significant catalytic activity in the hydrogenolysis of chromium that have been used for the industrial hydrogenolysis of esters to alcohols since the 1950s biomass-derived esters [4,5,6] and could replace copper-chromium catalysts that do not meet the [1,2,3]. Copper-zinc catalysts have been shown to possess significant catalytic activity in the highest environmental standards

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