In Situ TEM Investigation of Cu/ZnO Interface Formation Mechanisms Derived from the Decomposition of Copper–Zinc Hydroxycarbonate Precursors

The Cu/ZnO/Al 2 O 3 catalyst stands as one of the most efficient systems for methanol synthesis, water–gas shift, and CO 2 hydrogenation reactions. Critical to its performance is the formation of the CuO/ZnO interface during the thermal decomposition of catalyst precursors. In this work, we investigate binary CuO/ZnO catalyst precursors derived from copper/zinc hydroxycarbonates via ex situ and in situ transmission electron microscopy techniques, focusing on their structural evolution and crystal growth dynamics under varied calcination conditions. We reveal pronounced precursor heterogeneity, comprising zinc malachite and Cu-rich aurichalcite phases with distinct Cu/Zn ratios. We find that, besides calcination conditions, the effective mass transfer length scale in the precursor strongly influences the formation of CuO/ZnO interfaces and the derived CuO x /ZnO interfaces after reduction. In confined local regions of Cu-rich aurichalcite, localized mass transfer at the intermediate heating stage promotes preferential CuO x nucleation, followed by adjacent ZnO formation and dense CuO x /ZnO interfacial contact. In contrast, in extended precursor domains, increasing the temperature and/or prolonged heating promote large-scale mass transfer, particle coarsening, and pronounced CuO x /ZnO segregation, leading to interface structures reminiscent of conventional supported catalysts. These results show that temperature/time, precursor morphology, and compositional heterogeneity jointly determine the transport regime and, thus, the resulting interfacial architecture, providing mechanistic guidance for the rational design of Cu/ZnO catalysts with tailored interfaces.