Study on improving NH3 oxidation reaction performance of Pt/Al2O3 supported catalysts through optimization of porous structures

Aiming at the key issues of current vehicle Ammonia Slip Catalyst (ASC) catalysts, such as poor low-temperature activity, high noble metal content, and narrow operating window, this study aims to construct multi-scale pore structures in Al 2 O 3 supports of supported catalysts to regulate selective catalytic oxidation of NH 3 (NH 3 -SCO) across broad temperature ranges and space velocities by improving convective diffusion, conduction, migration, and adsorption processes within catalyst voids. Characterization results show that a series of catalyst supports with different pore structures was successfully prepared using different templates. Pt was loaded using an optimized supported catalyst preparation method. Meanwhile, the coating amount of the prepared catalyst on cordierite monolith substrates was significantly reduced, and NH 3 -SCO performance tests were conducted. The results indicate that single mesoporous structures have limited regulation on the intrinsic activity of catalysts, while macroporous structures enhance the influence of desorption and void diffusion of gas-phase reactants and products on catalytic reactions. In the presence of macroporous structures, the promotional effect of mesopores on NH 3 -SCO reactions is enhanced. Among all catalysts, hierarchical porous catalysts with larger pore diameters and better interconnected pore structures exhibit NH₃ conversion rates exceeding 99 % across the full temperature range of 200℃ - 500℃, with NH 3 concentrations below the regulatory limit of 10 ppm throughout the operating window. Macroporous structures and their pore diameters play a dominant role in regulating NH 3 -SCO reactions, particularly with stronger regulation at low temperatures. Increasing space velocity enhances the diffusion rate of NH 3 gas molecules while amplifying the influence of pore structure regulation on catalysts. Notably, compared with traditional Pt/Al 2 O 3 , pore structure regulation does not significantly increase the generation of N 2 O while effectively enhancing the catalytic activity of the ASC catalyst.