(691d) Controlling the Nanoarchitecture and Reaction Conditions to Enhance the VOC Oxidation Activity of Ag-TiO2 Catalysts

Catalyst deactivation, which results from active-metal sintering and surface area loss, accompanied by the formation of surface-covering coke deposits, remains a significant challenge in several industrial and environmental catalytic applications. Addressing this, we demonstrate a novel methodology of encapsulating and dispersing Ag nanoparticles in a reducible, mesoporous TiO₂ nanosphere to enhance both thermal stability and catalytic activity for VOC oxidation using n-butanol oxidation as a probe reaction.

Using a set of comprehensive material characterization techniques, collectively, we show that encapsulation approach helps in maintaining a uniform active-metal particle size distribution (2-5 nm) and promotes metal-support interactions by maximizing the number of interfacial sites. To examine the effects of active-metal placement, we also evaluate the performance of conventionally prepared, surface impregnated Ag-TiO₂ catalysts. In stark contrast to the encapsulated catalyst morphology, n-butanol oxidation profiles reveal that the surface impregnated Ag-TiO₂ catalysts suffer from significant silver sintering during cycled high-temperature (550°C) aging. This results in a continuous increase in the temperature required for 90% n-butanol conversion (T₉₀) from 220°C to 260°C, indicating thermally induced deactivation. To further enhance the thermal stability of the encapsulated Ag-TiO₂ catalysts, we demonstrate a post-synthesis solvothermal treatment methodology that can be used to effectively anchor active-metal to the support in addition to controlling the active-metal size and support structure. This treatment inhibits the agglomeration of both active-metal and support domains and leads to a catalyst with improved activity and maintains the T₉₀ of 200°C even after subjecting to repeated high-temperature (550°C) aging.

Finally, recognizing that industrial flue gas streams inevitably contain water vapor, we examine a constructive method of deliberately exposing the catalyst’s surface to water vapor before beginning the reaction. This simple method increases the abundance of ·O-H groups on the catalyst surface and enhances the rate of VOC oxidation reaction up to six-fold.