Multistep Reaction Pathway and Kinetics of the Thermal Decomposition of Catalyst Precursors: Copper(II)–Zinc Hydroxycarbonates

The Cu–Zn hydroxycarbonates serve as precursors for the preparation of CuO–ZnO and Cu–ZnO catalysts for methanol synthesis. In this study, the multistep thermal decomposition of Cu–Zn hydroxycarbonates with varying Cu:Zn ratios was investigated using a methodologically sound kinetic analysis procedure. The objective was to provide fundamental data regarding the heterogeneous reaction scheme and kinetics of multistep thermal decomposition. It is expected that the fundamental kinetic data will subsequently be optimized for the specific Cu–Zn hydroxycarbonate under specific reaction conditions and utilized for refining the processing conditions to prepare CuO–ZnO and Cu–ZnO. The Cu–Zn hydroxycarbonates with different Cu:Zn ratios were characterized as malachite, zincian malachite, aurichalcite, and hydrozincite, as well as these mixtures depending on the Cu:Zn ratio. For all Cu–Zn hydroxycarbonate samples, the multistep thermal decomposition was individually modeled as a partially overlapping five-step process to produce CuO–ZnO via poorly crystalline intermediate oxycarbonates or carbonates. The contribution and kinetic parameters of each reaction step in individual samples with specific Cu:Zn ratios were tabulated, which were correlated to the stoichiometry of the multistep reaction and compared between different samples.