Preparation of a highly active ternary Cu-Zn-Al oxide methanol synthesis catalyst by supercritical CO2 anti-solvent precipitation

Simon A Kondrat,Paul J Smith,Li Lu,Jonathan K Bartley,Stuart H Taylor,Michael S Spencer,Gordon J Kelly,Colin W Park,Christopher J Kiely,Graham J Hutchings

doi:10.1016/j.cattod.2018.03.046

Abstract

Methanol synthesis using Cu/ZnO/Al2O3 catalysts is a well-established industrial process. Catalyst development is always an important factor and this has resulted in the current fully optimised commercial catalyst that is prepared by co-precipitation via hydroxycarbonate precursors. Recently, the synthesis of a CuZn hydroxycarbonate precursor, analogous to the rare mineral georgeite, was reported to produce a high activity methanol synthesis catalyst. Here we report the addition of Al3+, the third component found in industrial catalysts, to the zincian georgeite-derived catalyst prepared using a supercritical CO2 anti-solvent precipitation methodology. The co-addition of an AlO(OH) sol to the Cu/Zn precursor solution was found to not disrupt the formation of the CuZn georgeite phase, while providing efficient mixing of the Al3+ within the material. The catalyst derived from the CuZn georgeite precursor phase doped with Al3+ showed a high level of methanol synthesis productivity, which was comparable to that of the binary CuZn georgeite derived catalyst. This material also exhibited enhanced stability during an accelerated ageing test compared to the non-Al doped zincian georgeite material. Performance was benchmarked against an industrially relevant Cu/ZnO/Al2O3 standard catalyst.

Highlights

Cu/ZnO/Al2O3 is a well-studied commercial catalyst used in the synthesis of methanol from syn-gas (CO, CO2 and H2) and in the lowtemperature water-gas shift reaction (LTS) [1,2]
It could have a direct role in the reaction mechanism through activation of CO2 or through generation of an active site resulting from a Cu-Zn interaction [7,8,9,10,11,12]
Metal acetate salts are chosen [21], it was found that aluminium triacetate was unsuitable due it its relatively high solubility in supercritical carbon dioxide

Summary

Introduction

Cu/ZnO/Al2O3 is a well-studied commercial catalyst used in the synthesis of methanol from syn-gas (CO, CO2 and H2) and in the lowtemperature water-gas shift reaction (LTS) [1,2] Both reactions are industrially important, with methanol being an important chemical intermediate having a worldwide demand exceeding 50 M tons per annum and the LTS reaction being used up-stream of many industrial processes for H2 production and CO removal [2]. Two structures for the active site are typically considered; namely a Cu-Zn surface alloy or an interfacial synergy between Cu/ZnO While this Cu-Zn interaction has formed the focus of many structure/ activity studies, the third component of the industrial catalyst, namely Al2O3 (and Al3+ in particular) is often overlooked. We report the successful addition of ∼20 at.% Al3+ into Cu/ZnO catalysts prepared by the SAS technique and investigate the effect of this promoter on the catalytic activity and stability

Experimental

Catalyst characterisation

Catalyst testing

Results and discussion

Conclusions