Lean NOx Reduction by In-Situ-Formed NH3 under Periodic Lean/Rich Conditions over Rhodium-Loaded Al-Rich Beta Zeolites
Lean NOx Reduction by In-Situ-Formed NH3 under Periodic Lean/Rich Conditions over Rhodium-Loaded Al-Rich Beta Zeolites
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DOI：
10.1021/acscatal.1c03396
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发表时间：
2021-09
期刊：
影响因子：
12.9
通讯作者：
Shunsaku Yasumura;Takashi Toyao;Z. Maeno;K. Shimizu
中科院分区：
文献类型：
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作者：
Shunsaku Yasumura;Takashi Toyao;Z. Maeno;K. Shimizu
为了合理设计周期性贫（NO + O2）和富（NO + H2）循环条件下的新型贫NOx还原催化剂，我们研究了在瞬态（贫Particrich）和升温条件下，Rh交换富Al（Si/Al = 5）β沸石（Rh 4 β5）上吸附的NO和NH3的反应。原位红外（IR）光谱的吸附物种收集，同时监测出口气体的质谱（MS）和另一个IR气体电池，使anoperandoanalysis的表面反应。用X射线吸收光谱（XAS）、程序升温还原（TPR）和红外光谱研究了催化剂结构的动态变化。在500 °C还原H2后，催化剂中同时存在Rh 0金属簇、Rh+和Rh 3+物种。在NO或NO + O2流动下，还原Rh 4 β5中的Rh+位点（NO储存位点）以[Rh（NO）2]+形式捕获NO，该形式在氧化（贫）条件下稳定。被捕获的NO被H2选择性还原为NH3。原位产生的NH3被一个布朗斯特酸位点（NH3存储位点）捕获。在下一个贫燃（NO + O2）阶段，NH3的捕获使NO还原为N2。最后，将Rh 4 β5应用于贫/富循环脱硝系统，并在周期性贫（0.1%NO +2%O2）/富（0.1%NO +2%H2）循环条件下进行脱硝。在稀燃期捕集的NOx在浓燃期被还原为吸附的NH3，其随后在下一稀燃期将NO还原为N2。
Toward the rational design of new lean NOxreduction catalysts under periodic lean (NO + O2) and rich (NO + H2) cycle conditions, we studied the reactions of adsorbed NO and NH3on Rh-exchanged Al-rich (Si/Al = 5) beta zeolites (Rh4β5) under transient (lean ↔ rich) and temperature ramping conditions. In situ infrared (IR) spectra of adsorbed species were collected while monitoring the outlet gas by mass spectrometry (MS) and another IR gas cell, enabling anoperandoanalysis of the surface reactions. Dynamic changes in the catalyst structure were studied by X-ray absorption spectroscopy (XAS), H2-temperature-programed reduction (TPR), andoperandoIR spectroscopy. Rh0metal clusters, Rh+, and Rh3+species were copresent in the catalyst after H2reduction at 500 °C. Under NO or NO + O2flow, the Rh+site (NO storage site) in the reduced Rh4β5 captured NO in the form of [Rh(NO)2]+, which was stable under oxidative (lean) conditions. The captured NO was selectively reduced by H2to NH3. The in-situ-generated NH3was captured by a Brønsted acid site (NH3storage site). The captured NH3reduced NO to N2in the next lean (NO + O2) period. Finally, Rh4β5 was applied to the lean de-NOxsystem under cyclic lean/rich conditions, accompanied by NOxreduction under periodic lean (0.1% NO + 2% O2)/rich (0.1% NO + 2% H2) cycles. The NOxtrapped in the lean period is reduced to adsorbed NH3in the rich period, which subsequently reduces NO to N2in the next lean period.