Dynamic Structural Evolution of [Rh(NO)2]+ Complex/Rh Metal Cluster in Zeolite during de-NOx via in situ Formed NH3 under Lean/Rich Periodic Conditions
Dynamic Structural Evolution of [Rh(NO)2]+ Complex/Rh Metal Cluster in Zeolite during de-NOx via in situ Formed NH3 under Lean/Rich Periodic Conditions
复制标题
稀/富周期条件下原位形成 NH3 脱硝过程中沸石中 [Rh(NO)2] 络合物/Rh 金属簇的动态结构演化
DOI：
10.1021/acs.jpcc.2c05705
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Shimizu Ken-ichi
中科院分区：
文献类型：
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作者：
Yasumura Shunsaku;Kato Taisetsu;Qian Yucheng;Toyao Takashi;Maeno Zen;Shimizu Ken-ichi
利用光谱技术和密度泛函理论（DFT）计算研究了丝光沸石（MOR）中Rh物质的动态结构演化。在这种情况下，x射线吸收光谱和红外光谱（IR）显示，在200°C NO流下，金属Rh被氧化为分离的[Rh(NO)2]+，而在随后的h2流下形成小的Rh金属团簇。Ab初始热力学分析表明，在NO和H2at 200℃下，MOR中可能的结构是[Rh(NO)2]+和Rh簇，这与实验观察一致。对负载Rh的al2o3的比较研究表明，MOR中的Al位增加了分离的Rh+物种的热力学稳定性，从而防止它们在NO下过度氧化为rh2o3。通过现场红外测量，观察了NO在H2flow下以[Rh(NO)2]+的形式被捕获，并选择性还原为nh3。RhMOR催化剂在200°C以上的周期性贫/富条件下表现出~ 60%的NOx转化率。过渡态计算表明，在[Rh(NO)2]+上NO还原为nh3的激活势垒（178 kJ/mol）高于Rh13(156 kJ/mol)，表明Rh金属团簇是更有利的nh3生成位点，其中Rh13催化NO还原为n2和N2O不如nh3生成有利，这与实验结果一致。结合贫（NO + O2）和富（NO + H2）条件下的operandoir实验，我们发现Rh物种（[Rh(NO)2]+贫和富条件下的Rh金属簇）的可逆动态结构演化是通过捕获NO、将其选择性还原为NH3和原位形成NH3选择性还原NO来进行非稳态脱硝的关键机制特征。
The dynamic structural evolution of Rh species in mordenite (MOR) zeolite was investigated usingin situspectroscopic techniques and density functional theory (DFT) calculations.In situX-ray absorption spectroscopy andoperandoinfrared (IR) revealed that metallic Rh species were oxidized to afford isolated [Rh(NO)2]+species under NO flow at 200 °C, whereas small Rh metal clusters are formed under the subsequent H2flow.Ab initiothermodynamics analysis shows that the plausible structures under NO and H2at 200 °C are [Rh(NO)2]+and Rh clusters in MOR, which is consistent with the experimental observations. A comparative study of Rh-loaded Al2O3suggests that Al sites in MOR increase the thermodynamic stability of isolated Rh+species and thus prevent their overoxidation to Rh2O3under NO. NO capture in the form of [Rh(NO)2]+and its selective reduction toward NH3under H2flow were observed byin situIR measurements. The RhMOR catalyst exhibited ∼60% of NOx conversion above 200 °C under periodic lean/rich conditions. Transition-state calculations showed that the activation barrier for NO reduction to NH3on [Rh(NO)2]+(178 kJ/mol) is higher than that for Rh13(156 kJ/mol), suggesting that Rh metal clusters are preferable NH3formation sites, where the Rh13-catalyzed NO reduction into N2and N2O was less preferable than NH3formation, which is consistent with the experimental results. Combined withoperandoIR experiments under lean (NO + O2) and rich (NO + H2) conditions, we show that the reversible dynamic structural evolution of Rh species ([Rh(NO)2]+↔ Rh metal clusters under lean and rich conditions) is a key mechanistic feature for unsteady-state de-NOx via the capture of NO, its selective reduction to NH3, and the selective reduction of NO with NH3formedin situ.