Arranging an ammonia oxidation process after the selective catalytic reduction of NOx by NH3 (NH3-SCR) system is an effective way for ensuring the DeNOx efficiency and controlling the slip ammonia. To improve operability and reduce operating costs in ammonia selective catalytic oxidation (NH3-SCO), developing feasible and efficient catalysts becomes meaningful. Herein, focusing on the dilemma of Ag/Al2O3 catalysts in NH3-SCO applications, Ag/MgAlOx catalysts with different support different crystalline phase structures (5 %Ag/MgAl-LDO and 5 %Ag/MgAl2O4) were innovatively synthesized and systematically evaluated application potential in NH3-SCO. Results indicated that the introduction of Mg apparently broadened reaction temperature window and catalytic performance of 5 %Ag/MgAl2O4 was higher than 5 %Ag/MgAl-LDO, while the N2 selectivity was completely opposite. The combination of series characterization and density functional theory (DFT) calculations revealed that 5 %Ag/MgAl2O4 surface has more Ag0 species with small particle size, which is favorable for ammonia adsorption and activated dehydrogenation to further promote reaction of NOx species, resulting in a higher NH3-SCO activity. In contrast, 5 %Ag/MgAl-LDO readily induces oxidized Ag species and Ag0 is more inclined to be present in large particle sizes, which is more conducive to dissociation of O2 to produce reactive O species (O*) leading to the peroxidation of ammonia to nitrate and thus, positively affects the improvement of N2 selectivity. Model catalyst 5 %Ag/MgAl-650 (mixed-phase) was prepared by controlling the roasting conditions and exhibited excellent catalytic performance in NH3-SCO with almost 93 % of NH3 oxidized at 250 °C (N2 selectivity up to 71 %). This work could afford theoretical support for the optimization and application of catalysts with high performance at low temperatures in selective catalytic oxidation of slip ammonia.

中文翻译：

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深入了解 Ag/MgAlOx 用于 NH3 选择性催化氧化的性能提升机制：从载体晶相结构的角度


在NH3选择性催化还原NOx（NH3-SCR）系统后安排氨氧化工艺是保证脱硝效率、控制逃氨的有效途径。为了提高氨选择性催化氧化（NH3-SCO）的可操作性并降低运行成本，开发可行且高效的催化剂变得有意义。本文针对Ag/Al2O3催化剂在NH3-SCO应用中的困境，创新合成了不同载体不同晶相结构的Ag/MgAlOx催化剂（5%Ag/MgAl-LDO和5%Ag/MgAl2O4）并系统评价了应用NH3-SCO 中的潜力。结果表明，Mg的引入明显拓宽了反应温度窗口，5%Ag/MgAl2O4的催化性能高于5%Ag/MgAl-LDO，而N2选择性则完全相反。串联表征和密度泛函理论（DFT）计算相结合表明，5%Ag/MgAl2O4表面具有较多粒径较小的Ag0物种，有利于氨吸附和活化脱氢，进一步促进NOx物种反应，从而产生NH3-SCO活性较高。相比之下，5%Ag/MgAl-LDO 很容易诱导氧化 Ag 物种，并且 Ag0 更倾向于以大粒径存在，这更有利于 O2 解离产生活性 O 物种 (O*)，从而导致过氧化氨转化为硝酸盐，从而对 N2 选择性的提高产生积极影响。通过控制焙烧条件制备了模型催化剂 5%Ag/MgAl-650（混合相），在 NH3-SCO 中表现出优异的催化性能，在 250 °C 时几乎 93% 的 NH3 被氧化（N2 选择性高达 71%）。 该工作为低温高性能催化剂在漏氨选择性催化氧化中的优化和应用提供理论支持。