Wu Hongli, Liu Weizao, Liang Ya, Liu Qingcai
College of Materials Science and Engineering, Chongqing University, Chongqing 400044, P. R. China.
College of Environment and Ecology, Chongqing University, Chongqing 400044, P. R. China.
Inorg Chem. 2023 Oct 23;62(42):17341-17351. doi: 10.1021/acs.inorgchem.3c02698. Epub 2023 Oct 6.
The conventional Mn-based catalysts suffer from lead toxicity and require other transition-metal oxides to enhance their resistance in the selective catalytic reduction of NO with ammonia (NH-SCR). Herein, we found that the incorporation of inert silica into pure MnO effectively improved the Pb resistance. The NO conversion of the MnO-SiO-Pb catalyst was nearly 55% higher than that of the MnO-Pb catalyst, exhibiting enhanced activity at lower temperatures (150-225 °C). To reveal the essential roles at the molecular level, the types and numbers of surface acidity, nitrate species, and catalytic cycle were established through experimental analysis and theoretical calculations of catalysts. The presence of PbCl occupied the active Mn sites, resulting in an obvious decline in the Brønsted acid sites (B-NH) and the oxidation performance, and the NH-SCR cycle was energetically less favorable on the MnO-Pb catalyst. Conversely, SiO played a crucial role in preserving the activity of Mn sites on the MnO-SiO-Pb catalyst by preferentially bonding with PbCl, generating more active intermediates. Significantly, this work provided mechanistic insights into the role of SiO in regulating the surface acidity, oxidation performance, and stability of active Mn sites, which is helpful for the design of Mn-based catalysts with high Pb resistance for the NH-SCR reaction.
传统的锰基催化剂存在铅毒性问题，并且在氨选择性催化还原NO（NH-SCR）过程中需要其他过渡金属氧化物来增强其抗性。在此，我们发现将惰性二氧化硅掺入纯MnO中可有效提高抗铅性。MnO-SiO-Pb催化剂的NO转化率比MnO-Pb催化剂高出近55%，在较低温度（150-225°C）下表现出增强的活性。为了在分子水平上揭示其本质作用，通过对催化剂的实验分析和理论计算确定了表面酸度、硝酸盐物种的类型和数量以及催化循环。PbCl的存在占据了活性锰位点，导致布朗斯特酸位点（B-NH）和氧化性能明显下降，并且NH-SCR循环在MnO-Pb催化剂上在能量上不太有利。相反，SiO通过优先与PbCl结合，在保持MnO-SiO-Pb催化剂上锰位点的活性方面发挥了关键作用，生成了更多的活性中间体。值得注意的是，这项工作为SiO在调节表面酸度、氧化性能和活性锰位点稳定性方面的作用提供了机理见解，这有助于设计用于NH-SCR反应的具有高抗铅性的锰基催化剂。
