Microscopic Investigation of H2 Reduced CuO x /Cu(111) and ZnO/CuO x /Cu(111) Inverse Catalysts: STM, AP-XPS, and DFT Studies

Understanding the reduction mechanism of ZnO/CuO x interfaces by hydrogen is of great importancein advancingthe performance of industrial catalysts used for CO and CO2 hydrogenation to oxygenates, the water-gas shift, and the reformingof methanol. Here, the reduction of pristine and ZnO-modified CuO x /Cu(111) by H-2 was investigatedusing ambient-pressure scanning tunneling microscopy (AP-STM), ambient-pressureX-ray photoelectron spectroscopy (AP-XPS), and density functionaltheory (DFT). The morphological changes and reaction rates seen forthe reduction of CuO x /Cu(111) and ZnO/CuO x /Cu(111) are very different. On CuO x /Cu(111), perfect 44 and 29structures displayed a very low reactivity toward H-2 atroom temperature. A long induction period associated with an autocatalyticprocess was observed to enable the reduction by the removal of chemisorbednonlattice oxygen initially and lattice oxygen sequentially at theCuO( x )-Cu interface, which led tothe formation of oxygen-deficient 5-7 hex andhoneycomb structures. In the final stages of the reduction process,regions of residual oxygen species and metallic Cu were seen. Theaddition of ZnO particles to CuO x /Cu(111)opened additional reaction channels. On the ZnO sites, the dissociationof H-2 was fast and H adatoms easily migrated to adjacentregions of copper oxide. This hydrogen spillover substantially enhancedthe rate of oxygen removal, resulting in the rapid reduction of thecopper oxide located in the periphery of the zinc oxide islands withno signs of the reduction of ZnO. The deposited ZnO completely modifiedthe dynamics for H-2 dissociation and hydrogen migration,providing an excellent source for CO2 hydrogenation processeson the inverse oxide/metal system.

Automated summary

Understanding the reduction mechanism of ZnO/CuOx interfaces by hydrogen is crucial for improving the performance of industrial catalysts in various hydrogenation processes. This study investigated the reduction of pristine and ZnO-modified CuOx/Cu(111) using AP-STM, AP-XPS, and DFT. The reduction behaviors and reactions rates differed significantly between CuOx/Cu(111) and ZnO/CuOx/Cu(111). The addition of ZnO particles facilitated the dissociation of H2 and promoted the rapid reduction of copper oxide, leading to enhanced CO2 hydrogenation on the inverse oxide/metal system.