Analogous Mechanistic Features of NH3-SCR over Vanadium Oxide and Copper Zeolite Catalysts
Analogous Mechanistic Features of NH3-SCR over Vanadium Oxide and Copper Zeolite Catalysts
复制标题
DOI：
10.1021/acscatal.1c02860
复制
发表时间：
2021-08-23
期刊：
影响因子：
12.9
通讯作者：
Shimizu, Ken-ichi
中科院分区：
文献类型：
--
作者：
Kubota, Hiroe;Toyao, Takashi;Shimizu, Ken-ichi
还原/氧化半循环的选择性催化还原NO与NH3（NH3-SCR）在200 ℃下进行了研究，使用原位和操作光谱提出了一个一般的机制，为四种不同的催化剂（TiO 2负载和散装钒氧化物和Cu-AFX和Cu-CHA沸石）。还原半循环是由刘易斯酸中心[V（V）或Cu（II）; L-NH3]上的NH3与NO反应引发的，随后是布朗斯台德酸中心（B-NH3）上的NH3与NO的逐渐反应;这导致在表面上形成V（IV）或Cu（I）和质子（H+），沿着N-2和H2O。还原半循环的UV-vis测量表明，N-2持续产生，直到表面V（V）或Cu（II）物种耗尽。随后在O-2下还原的催化剂的再氧化导致V（V）或Cu（II）的再生和表面H+的反应，产生H2O（氧化半循环）。在NO + O-2条件下B-NH3和L-NH3的消耗速率高于NO条件下的消耗速率，这一现象已在文献中报道过，并基于V（V）/ V（IV）或Cu（II）/Cu（I）的连续还原/氧化进行了解释，其中再生的V（V）或Cu（II）位点在随后的（第二）还原半循环中重复使用。也就是说，在通过再氧化回收V（V）或Cu（II）时，剩余的B-NH3物质与供应的NO反应以产生N-2;这表明B-NH3不是旁观者，而是NH3的储库，以可能通过NH3或HONO物质的迁移参与第二还原半循环。这些结果为NH3-SCR的一般机理提供了全面的证据，发现其适用于V和Cu催化剂。
Reduction/oxidation half-cycles of the selective catalytic reduction of NO with NH3 (NH3-SCR) at 200 degrees C were investigated using in situ and operando spectroscopies to propose a general mechanism for four different catalysts (TiO2-supported and bulk vanadium oxides and Cu-AFX and Cu-CHA zeolites). The reduction half-cycle is initiated by the reaction of NH3 on Lewis acid sites [V(V) or Cu(II); L-NH3] and NO, followed by the gradual reaction of NH3 on Bronsted acid sites (B-NH3) and NO; this results in the formation of V(IV) or Cu(I) and protons (H+) on the surface, along with N-2 and H2O. The UV-vis measurements for the reduction half-cycle indicate that N-2 is continuously generated until the surface V(V) or Cu(II) species is depleted. The subsequent reoxidation of the reduced catalysts under O-2 leads to the regeneration of V(V) or Cu(II) and the reaction of surface H+, yielding H2O (oxidation half-cycle). The higher consumption rates of B-NH3 and L-NH3 under NO + O-2 than those under NO, which has been previously reported in the literature, were explained based on the continuous reduction/oxidation of V(V)/ V(IV) or Cu(II)/Cu(I) where the regenerated V(V) or Cu(II) site is reused in the subsequent (second) reduction half-cycle. Namely, upon the recovery of V(V) or Cu(II) via reoxidation, the leftover B-NH3 species react with the supplied NO to yield N-2; this suggests that B-NH3 is not a spectator but a reservoir of NH3 to participate in the second reduction half-cycle possibly via the migration of NH3 or HONO species. These results provide comprehensive evidence of the general mechanism of NH3-SCR, which was found to be applicable to both V and Cu catalysts.