Pt anchored in the skeleton of rice husk-based ZSM-5 for excellent catalytic VOC oxidation: structure–activity relationship and environmental impact assessment

Abstract

ZSM-5 molecular sieves (ZSM-5-T1, ZSM-5-T2, ZSM-5-T3) were synthesized using SiO₂, SiO₂-8.7% C, and SiO₂-23.6% C as templates from rice husk powder, respectively. Pt species were fixed within the ZSM-5 skeleton via the isovolumetric impregnation method, and the resulting catalysts were employed for the efficient oxidation of toluene (C₇H₈). Notably, Pt/ZSM-5-T2 exhibited the highest C₇H₈ catalytic oxidation activity (R_{175 °C} = 0.733 μmol g⁻¹ s⁻¹, WHSV = 60 000 mL h⁻¹ g⁻¹) among the three variants. Furthermore, this catalyst displayed excellent water resistance when exposed to various concentrations of water vapor (2 vol%, 5 vol%, 8 vol% and 10 vol%) during the activity test. The characterization results provided insight into the exceptional catalytic performance of the Pt/ZSM-5-T2 catalyst, attributing it to its high specific surface area, appropriate hydrophilicity, abundant Lewis acid sites, and a high Pt⁰/(Pt⁰ + Pt²⁺) ratio. In situ DRIFTS analysis further suggested that the key step in the oxidation of C₇H₈ to benzyl alcohol involves C–H cleavage on Pt/ZSM-5. Simultaneously, the application of a life-cycle assessment (LCA) revealed that this strategy, involving the substitution of chemicals with biomass, led to a remarkable 41–43% reduction in carbon footprint. This environmentally friendly approach underscores the potential for repurposing rice husk powder waste. Pt/ZSM-5-T2 meets the requirements for practical applications, paving the way for sustainable resource utilization in the realm of environmental preservation.