Reversible and Irreversible Structural Changes in Cu/ZnO/ZrO2 Catalysts during Methanol Synthesis

The structure and chemical state of heterogeneous catalysts are closely related to their operational stability. Knowing these relationships as precisely as possible is thus essential for further catalyst development. This work focuses on the deactivation of a Cu/ZnO/ZrO2-type catalyst for methanol synthesis. Experiments were performed in a parallel setup, with which time-dependent changes in the catalyst material can be observed. Elucidation of potential deactivation pathways is described for catalyst aging at different times on stream (0, 50, 935 h). Data from X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, N-2 physisorption, and transmission electron microscopy measurements reveal that sintering of Cu-0 domains and restructuring within ZnO domains mainly contribute to deactivation. Subsequent reactivation by reduction (in H-2/N-2) reverts the observed structural changes only to a limited extent. Moreover, this work highlights the participation of ZrO2 as a promoter and reveals redispersion of zirconia after initial reduction.