Dopant-Induced Modification of Active Site Structure and Surface Bonding Mode for High-Performance Nanocatalysts: CO Oxidation on Capping-free (110)-oriented CeO_2:Ln (Ln = La-Lu) Nanowires

摘要

Active center engineering at atomic level is a grand challenge for catalyst design and optimization in many industrial catalytic processes. Exploring new strategies to delicately tailor the structures of active centers and bonding modes of surface reactive intermediates for nanocatalysts is crucial to high-efficiency nanocatalysis that bridges heterogeneous and homogeneous catalysis. Here we demonstrate a robust approach to tune the CO oxidation activity over CeO_2 nanowires (NWs) through the modulation of the local structure and surface state around Ln_ce′ defect centers by doping other lanthanides (Ln), based on the continuous variation of the ionic radius of lanthanide dopants caused by the lanthanide contraction. Homogeneously doped (110)-oriented CeO_2:Ln NWs with no residual capping agents were synthesized by controlling the redox chemistry of Ce(Ⅲ)/Ce(Ⅳ) in a mild hydrothermal process. The CO oxidation reactivity over CeO_2:Ln NWs was dependent on the Ln dopants, and the reactivity reached the maximum in turnover rates over Nd-doped samples. On the basis of the results obtained from combined experimentations and density functional theory simulations, the decisive factors of the modulation effect along the lanthanide dopant series were deduced as surface oxygen release capability and the bonding configuration of the surface adsorbed species (i.e., carbonates and bicarbonates) formed during catalytic process, which resulted in the existence of an optimal doping effect from the lanthanide with moderate ionic radius.