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Highlights: [•] Mesoporous CeO2 supports were synthesized using two different methods. [•] Preparation method of CeO2 notably affected the structure and activity of Ag catalyst. [•] Ag/CeO2-HP showed higher catalytic activity for CO oxidation than Ag/CeO2-SP. [•] More oxygen vacancies and species were formed on the CeO2-HP surface. [ABSTRACT FROM AUTHOR]

An understanding of active species–metal oxide support interaction is a necessary prerequisite for finely tuning the catalytic performance of Ag-based catalysts. To shed light on the interrelationship between Ag structures and acidic sites of acidic supports, a series of Ag/Al-SBA-15 catalysts with different Si/Al ratios were prepared using in situ “pH-adjusting” method and tested for catalytic CO oxidation. Of all the catalysts employed, the one with a Si/Al molar ratio of 200 (Ag/MAS 200) outperformed other catalysts in terms of activity and durability. 27 Al NMR and 1 H NMR results showed that the octahedrally coordinated extra-framework Al connected to the framework via oxygen atoms suppressed the formation of H-bonded SiOH groups, resulting in the formation of highly dispersed Ag nanoparticles with high catalytic activity. In the meantime, the presence of Ag 2 O particles formed over the framework Al with bridging hydroxyl groups considerably deteriorated the catalytic performance. However, the Ag/MAS 200 catalyst exhibited a striking feature: that is, the bulk Ag 2 O species are easily reduced by CO at room temperature, leading to “ in situ formation” of metallic Ag particles during CO oxidation even in the presence of high concentration of O 2 . This unique property caused the induction period (ca. 270 min) and gradually enhanced the catalytic activity, eventually reaching a high and steady-state CO conversion (85%). [ABSTRACT FROM AUTHOR]

Highlights: [•] Direct synthesis calcination method was developed to synthesize Ag nanoparticles. [•] Highly dispersed uniformly sized Ag nanoparticles were supported on silica. [•] DDA was a key factor in obtaining ordered support and dispersed silver particles. [•] High activity in CO oxidation (T98%=20°C) was obtained. [ABSTRACT FROM AUTHOR]

Abstract: The structural properties of Ag/SBA-15 catalysts with various Ag loading after pretreatment under different atmosphere, i.e., O2, Ar and H2, in relation to their activities on CO oxidation were investigated. N2 adsorption–desorption results showed that the pretreatment atmosphere had a negligible effect on the physical structure of all catalysts. Interestingly, it was found that different pretreatment atmosphere (Ar, O2) and Ag loading exhibited a large difference on the structure of silver catalyst and their catalytic activity. For Ag/SBA-15 catalyst with low silver loading (≤6wt%), Ar pretreatment resulted in the highest activity for CO oxidation. However, the highest catalytic performance was observed after oxygen pretreatment over the silver catalyst with high loading (>6wt%). UV–vis and H2-TPR results showed Ar pretreatment and Ag loading strongly affected the states of Ag species for the silver catalysts, which were changed from metal Ag (≤4wt%) to a mixture of Ag and Ag2O (≥6wt%). Moreover Ar pretreatment was favorable for the formation of small Ag particles for Ag/SBA-15 catalyst with low Ag loading. When the silver loading is increased, the heavy aggregation of silver particles occurred after Ar pretreatment, resulting in the decrease of TOF for CO oxidation. O2 pretreatment was conductive to the formation of subsurface oxygen species on the larger silver particles for Ag/SBA-15 catalyst with high Ag loading, which resulted in the increase of TOF for CO oxidation. It was evident that small metal Ag particles was key factor of the higher catalytic activity for Ag/SBA-15 catalyst with low Ag loading, while a large number of subsurface oxygen species played an important effect on the higher catalytic activity for Ag/SBA-15 catalyst with high Ag loading. [Copyright &y& Elsevier]

Abstract: We report an Ag/SBA-15 catalyst with low loading (1.42wt%) that shows excellently high activity in CO oxidation at room temperature after oxygen pretreatment at 900°C. A 98% conversion of CO is achieved at 20°C (T 98 =20°C). An evaporation–deposition–diffusion mechanism for Ag/SBA-15 catalyst is proposed. The oxygen adsorbate-induced decrease in the surface-free energy at 900°C induces the evaporated silver atoms to be redeposited on the support, and meanwhile diffuse into the channels of SBA-15, forming more highly dispersed small silver particles inside the channels. The favorable structure of silver catalyst for CO oxidation is believed to arise from the synergistic effect of oxygen atmosphere, high temperature (900°C), and the channel of SBA-15. In addition, the formation of Ag+ on the surface of support after oxygen pretreatment at 900°C is also suggested to be essential for the following reduction and high catalytic activity for CO oxidation. [Copyright &y& Elsevier]