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Understanding the atomic diffusion process of a metal oxide helps with the design of more effective oxygen carriers for chemical looping with oxygen uncoupling (CLOU). Herein we investigated the atomic diffusion process in both slab and bulk CuO with varying oxygen vacancy (VO) under CLOU conditions using density functional theory (DFT) calculations and molecular dynamic (MD) simulation based on the neural network (NN) potential. Although the diffusions of both the Cu and the O atoms are important for the slab model, the O atoms’ outward diffusion to fill surface VOdominates the interlayer diffusion. In contrast, Cu atoms barely diffuse in the bulk model, and the diffusion process is dominated by O atoms through the VO. The MD-estimated chemical diffusion coefficients (10–9–10–13m2/s) and activation barriers (1.14–1.34 eV) of both models are consistent with those experimentally measured values. The diffusion coefficient increases with increasing VO, and the values of the slab model are two orders of magnitude higher than those of the bulk model with a similar VO. These results indicate that the chemical diffusion is dominated by the surface instead of the bulk, and the diffusion in the bulk only becomes important when it becomes the frontier of oxygen uncoupling, i.e., grain boundary between CuO and Cu2O. The majority of diffusion species (O atom or vacancy) and process revealed in this study provide atomic insight into the diffusion in CuO-based materials.

Catalytic conversion of CO2to CO via reverse water gas shift (RWGS) and CH4via methanation are competing reactions that simultaneously happen on Ni-based catalysts, and selective control of the reactions is of great importance to subsequent applications. Herein, conversion of CO2on Mo3O5/Ni(111) with varying MoOxcoverages was investigated using a combination of density functional theory (DFT) calculation and microkinetic modeling. The overall reaction proceeds through sequential RWGS to CO and CO methanation. The coordinatively unsaturated Mo (Moov) site at the interface of Mo3O5/Ni(111) enhances CO2adsorption and facilitates C–O cleavage over the bare Ni(111), leading to more favorable CO2direct dissociation to CO formation than the carboxyl and formate pathways. The oxophilic Moovalso facilitates hydrogenation of CO to HCO and decomposition of CHO to CH and O. On Mo3O5/4 × 4 Ni(111), the enhanced hydrogenation and C–O breakage activity resulted in CH4as the selective product. On Mo3O5/3 × 3 Ni(111), in contrast, the reduced size of the surface Ni ensembles caused the d-band center of surface Ni sites to shift downward, weakened CO adsorption, and reduced the hydrogenation activity, resulting in CO as the dominant product. Microkinetics analysis revealed that direct CO2dissociation was the dominant path on Mo3O5/4 × 4 Ni(111) and the interfacial sites of Mo3O5/4 × 4 Ni(111) were primarily covered by O and OH. The rate-limiting step on Mo3O5/Ni(111) was the regeneration of Mo3O5. Consistent with the experimental results, the microkinetics also predicts that CH4is selectively produced on Mo3O5/4 × 4 Ni(111) whereas CO is the primary product on Mo3O5/3 × 3 Ni(111).