Development of CuO/ZnO/Al2O3-hydrotalcite −based catalysts for middle temperature water gas shift reaction: Impact of calcination temperature and residual carbonates

Abstract

A series of Cu/ZnO/Al2O3 catalysts are synthesized using a reverse co-precipitation method and subjected to calcination at different temperatures ranging from 300 to 650 °C. Characterization of the resulting powders is carried out through ICP, N2-physisorption, XRD, TGA, H2-TPR, N2O chemisorption and SEM techniques. Subsequently, the catalytic performance of the final samples is assessed in the medium-temperature water gas shift reaction across a broad temperature range from 200 to 330 °C. The precursor predominantly featured a hydrotalcite-like structure, undergoing decomposition through three main stages by losing structural H2O and CO2 molecules. All catalysts demonstrated stable performance without by-products during accelerated aging under reaction conditions. The results revealed that the partial elimination of carbonate ions at 300 °C resulted in easily reducible and consequently less thermally stable active sites. For calcined samples at 450 °C and 550 °C the thermal sintering played a pivotal role, leading the less copper surface area and subsequently higher CO slip values. In the case of the calcined sample at 650 °C, despite larger CuO and ZnO crystals, a trade-off between the emission of high-temperature carbonates and thermal sintering led to acceptable activity and thermal stability. Ultimately, the highest Cu surface are of 222 m2gr cat −1 along with the lowest amount of CO slip are observed for calcined sample at 350 °C, attributed to an optimal amount of carbonate, resulting in the superior catalytic performance. This effective balance between thermal sintering and the amount of residual carbonates yielded a final catalyst with outstanding activity and stable performance.