Supercritical Antisolvent Precipitation of Amorphous Copper-Zinc Georgeite and Acetate Precursors for the Preparation of Ambient-Pressure Water-Gas-Shift Copper/Zinc Oxide Catalysts.

Paul J Smith,Graham J Hutchings,Jonathan K Bartley,Stuart H Taylor,Michael S Spencer,Simon A Kondrat,James H Carter,Philip A Chater

doi:10.1002/cctc.201601603

Abstract

A series of copper–zinc acetate and zincian georgeite precursors have been produced by supercritical CO2 antisolvent (SAS) precipitation as precursors to Cu/ZnO catalysts for the water gas shift (WGS) reaction. The amorphous materials were prepared by varying the water/ethanol volumetric ratio in the initial metal acetate solutions. Water addition promoted georgeite formation at the expense of mixed metal acetates, which are formed in the absence of the water co‐solvent. Optimum SAS precipitation occurs without water to give high surface areas, whereas high water content gives inferior surface areas and copper–zinc segregation. Calcination of the acetates is exothermic, producing a mixture of metal oxides with high crystallinity. However, thermal decomposition of zincian georgeite resulted in highly dispersed CuO and ZnO crystallites with poor structural order. The georgeite‐derived catalysts give superior WGS performance to the acetate‐derived catalysts, which is attributed to enhanced copper–zinc interactions that originate from the precursor.

Highlights

The water-gas-shift (WGS) reaction (CO + H2OÐH2 + CO2) is of central importance for the industrial production of hydrogen and depletion of CO in syngas streams.[1,2] the WGS process is intimately linked with ammonia synthesis and hydrogen polymer electrolyte membrane fuel cell (PEMFC) applications for which CO is a poison
We have shown that the presence of water has significant implications on the physicochemical properties of copper–zinc precipitates prepared by supercritical CO2 antisolvent (SAS) precipitation
Optimum SAS precipitation occurs in the absence of water, with gas-like mixing between EtOH and supercritical CO2 (scCO2) resulting in intimately mixed, high-surface-area acetates

Summary

Introduction

We have recently prepared zincian georgeite, an amorphous copper–zinc hydroxycarbonate, by supercritical CO2 antisolvent (SAS) precipitation and have demonstrated that it can be used to prepare Cu/ZnO catalysts that are highly active and stable for the WGS reaction.[30] This enhanced stability removes the necessity to incorporate alumina into the catalyst This procedure enables the processing of high-purity materials devoid of residual catalyst poisons, including nitrates[28] and alkali metals,[31] and does not require delicate control of a broad range of conditions such as pH. The catalyst performances could be correlated to their structures, which highlighted the importance of the catalyst precursor phase

Results and Discussion

Conclusions

Conflict of interest