Copper oxide and zinc oxide based (Cu/ZnO) catalysts are widely used for a variety of chemical transformations, including methanol synthesis, steam reforming of methanol, lower alkene purification due to their low cost and high performance characteristics. Among several known synthesis methodologies of Cu/ZnO catalysts, the coprecipitation method is a popular one, which produce hydroxycarbonate precursors. Although these carbonates are decomposed during the final calcination steps, a small amount (ppm level) of carbonate moieties could be present in the product of Cu/ZnO catalysts. These carbonates could affect the performance of Cu/ZnO catalysts in some applications, depending on its sensitivity on carbonate. In this context, the following contribution attempts to investigate the thermal decomposition of the residues of carbonate that remain in the calcined Cu/ZnO catalyst at a few ppm levels. A comprehensive knowledge on the nature of these carbonate species would be developed by using analytical techniques such as in situ XRD and TG/MS. It is found that the coprecipitation of Cu2+ and Zn2+ salts with a carbonate precipitating agent produces different hydroxycarbonate precursors such as malachite and aurichalcite. After the calcination at 673 K, the main crystalline phases are copper oxide and zinc oxide. However, the usual calcination conditions are not fully effective to completely eliminate hydroxides carbonates. The above studies indicate a possible in-situ thermal treatment may be important if the Cu/ZnO catalysts would be used for the applications with sensitivity on carbonates species.

In situ characterization of the residual carbonates in Cu/ZnO catalysts

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