Wang Chunxue, Li Yuan, Li Zhao, Meng Caixia, Ma Yixing, Sun Xin, Ning Ping, Li Kai, Wang Fei
Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming, 650500, China.
National Regional Engineering Center for Recovery of Waste Gases from Metallurgical and Chemical Industries, Kunming, 650500, China.
Environ Sci Technol. 2024 Aug 18. doi: 10.1021/acs.est.4c06499.
Ammonia (NH) slip from diesel vehicle aftertreatment systems and internal combustion engines fueled by NH or NH/H poses serious environmental problems. Ag-based catalysts are widely used for the selective catalytic oxidation of NH to N (NH-SCO), and their performance is greatly dependent on the state of Ag, which is influenced by the anchoring sites on the support. Despite efforts to identify the direct anchoring sites of metal atoms on TiO, conflicting views persist. Here, we compared the correlation between Ag dispersion and the content of hydroxyl (OH) groups or defects on TiO and conducted density functional theory (DFT) calculations, and the results confirmed that the surface OH groups of TiO serve as the direct anchoring sites for Ag. By modulating the OH group content through thermal induction, the optimal OH group content on TiO-800 resulted in more metallic Ag nanoparticles (Ag NPs) in larger sizes, leading to the development of an excellent NH-SCO catalyst. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), kinetic studies, and DFT calculations suggested that more Ag NPs in larger sizes on 10Ag/TiO-800 were conducive to O activation and NH dissociation. Our findings provide new insights for designing efficient NH-SCO catalysts, and OH groups as direct anchoring sites could be extended to other metals and supports for the rational design of catalysts.
柴油车后处理系统以及以氨或氨/氢为燃料的内燃机中产生的氨（NH₃）泄漏会引发严重的环境问题。银基催化剂被广泛用于将氨选择性催化氧化为氮气（NH₃-SCO），其性能很大程度上取决于银的状态，而银的状态受载体上锚固位点的影响。尽管人们努力确定金属原子在二氧化钛（TiO₂）上的直接锚固位点，但仍存在相互矛盾的观点。在此，我们比较了银的分散度与TiO₂上羟基（OH）基团含量或缺陷之间的相关性，并进行了密度泛函理论（DFT）计算，结果证实TiO₂的表面OH基团是银的直接锚固位点。通过热诱导调节OH基团含量，TiO₂-800上的最佳OH基团含量导致形成更多更大尺寸的金属银纳米颗粒（Ag NPs），从而开发出一种优异的NH₃-SCO催化剂。此外，原位漫反射红外傅里叶变换光谱（DRIFTS）、动力学研究和DFT计算表明，10Ag/TiO₂-800上更多更大尺寸的Ag NPs有利于氧活化和氨解离。我们的研究结果为设计高效的NH₃-SCO催化剂提供了新的见解，并且作为直接锚固位点的OH基团可扩展到其他金属和载体，以实现催化剂的合理设计。
