Abstract
Herein, to investigate the pore effect on toluene catalytic oxidation activity, novel supports for Pt nanoparticles—ZSM-5 foam (ZF) fabricated using polyurethane foam (PUF) templates and pore-modified ZSM-5 foam (ZF-D) treated by acid etching, comparing with conventional ZSM-5 and pore-modified ZSM-5 (ZSM-5-D), were successfully synthesized. Pt nanoparticles were loaded on series ZSM-5 supports by the impregnation method. The Pt loaded on ZF-D (Pt/ZF-D) showed the highest activity of toluene catalytic combustion (i.e., T90 = 158 °C), with extraordinary stability and an anti-coking ability. Based on various catalysts characterizations, the unique macropores of ZF facilitated the process of acid etching as compared to conventional ZSM-5. The mesopores volume of ZF-D significantly increased due to acid etching, which enlarged toluene adsorption capacity and led to a better Pt distribution since some Pt nanoparticles were immobilized into some mesopores. Specifically, the microporous distribution was centered in the range of 0.7–0.8 nm close to the molecular diameter of toluene (ca. 0.67 nm), which was key to the increasing toluene diffusion rate due to pore levitation effect of catalysts and accessibility of metal. Furthermore, the reducibility of Pt nanoparticles was improved on Pt/ZF-D, which enhanced the activity of toluene catalytic oxidation.
Highlights
Volatile organic compounds (VOCs), as one of the most important precursors of air pollution for causing many environmental problems, are generated by the vehicle exhaust emission, industrial processes emission, and volatile chemical products [1,2,3,4,5]
Results of N2 adsorption–desorption indicate that typical hierarchical porous structures and the enlarged pore volume of Pt loaded on ZSM-5 foam (ZF)-D (Pt/ZF-D) can be beneficial for the diffusion and adsorption of the relatively large molecules such as toluene
Macro-meso-microporous ZF-D was successfully synthesized by a nitric acid etching strategy, and Pt nanoparticles were loaded onto ZF and ZF-D respectively using the wetness impregnation method
Summary
Volatile organic compounds (VOCs), as one of the most important precursors of air pollution for causing many environmental problems, are generated by the vehicle exhaust emission, industrial processes emission, and volatile chemical products [1,2,3,4,5]. Over the past several decades, developing techniques such as adsorption [6,7], catalytic combustion [8], thermal incineration [9], biological processes, plasma catalytic oxidation [10], and photocatalytic degradation, etc. Have attracted great attention to remove VOCs. Among them, catalytic combustion is a well-known technology of high catalytic performance, economic feasibility, high selectivity, low operation cost, and non-organic by-products for its approximately completely catalytic oxidation of VOCs into CO2 and H2O at low temperatures [11,12,13]. According to the previous studies, it is reported that lower reaction temperature is more economical for the catalytic oxidation of VOCs [14] so that noble-metal catalysts with high activity, high selectivity, and low activation energies have attracted much attention [15]. Pt-based catalysts are widely applied for total catalytic oxidation of VOCs due to their extraordinary low-temperature activities [16]
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