Effect of the modification of alumina supports with chloride on the structure and catalytic performance of Ag/Al_(2)O_(3)catalysts for the selective catalytic reduction of NO_(x)with propene and H_(2)/propene  

Cl^(-)改性对Ag/Al_(2)O_(3)催化剂结构及其催化C_(3)H_(6)-SCR和H_(2)/C_(3)H_(6)-SCR反应性能的影响

作　　者：Jia Wang Rui You Kun Qian Yang Pan Jiuzhong Yang Weixin Huang 王嘉;尤瑞;千坤;潘洋;杨玖重;黄伟新(中国科学技术大学化学物理系,中国科学院能量转换材料重点实验室,安徽省教育厅表界面化学与能源催化重点实验室,合肥微尺度物质科学国家研究中心,安徽合肥230026;中国科学技术大学国家同步辐射实验室,安徽合肥230029;洁净能源国家实验室,辽宁大连116023)

机构地区：[1]Hefei National Laboratory for Physical Sciences at the Microscale Key Laboratory of Surface and Interface Chemistry and Energy Catalysis of Anhui Higher Education Institutes and Department of Chemical Physics,University of Science and Technology of China,Hefei 230026,Anhui,China [2]National Synchrotron Radiation Laboratory,University of Science and Technology of China,Hefei 230029,Anhui,China [3]Dalian National Laboratory for Clean Energy,Dalian 116023,Liaoning,China

出　　处：《Chinese Journal of Catalysis》2021年第12期2242-2253,共12页催化学报（英文）

基　　金：国家自然科学基金(21703227);中国科学技术大学(KY2060000176);中国科学院;教育部长江学者奖励计划。

摘　　要：The effect of the modification of an alumina support with chloride on the structure and the catalytic performance of Ag/Al_(2)O_(3)catalysts(SA)was investigated for the selective catalytic reduction(SCR)of NO using C_(3)H_(6)or H_(2)/C_(3)H_(6)as reductants.The Ag/Al_(2)O_(3)catalyst and Cl^(–)-modified Ag/Al_(2)O_(3)catalysts(SA-Cl)were prepared by a conventional impregnation method and characterized by X-ray diffraction,Brunauer-Emmett-Teller isotherm analysis,electron probe microanalysis,transmission electron microscopy,UV-Vis diffuse reflectance spectroscopy,X-ray photoelectron spectroscopy,and hydrogen temperature-programmed reduction.The catalytic activities in the C3H6-SCR and H_(2)/C3H6-SCR reactions were evaluated,and the reaction mechanism was studied using in situ diffuse reflectance infrared Fourier transform spectroscopy and synchrotron vacuum ultraviolet photoionization mass spectroscopy(SVUV-PIMS).We found that Cl^(-)modification of the alumina-supported Ag/Al_(2)O_(3)catalysts facilitated the formation of oxidized silver species(Ag_(n)^(ᵟ+))that catalyze the moderate-temperature oxidation of hydrocarbons into partial oxidation products(mainly acetate species)capable of participating in the SCR reaction.The low-temperature promoting effect of H_(2)on the C3H6-SCR("hydrogen effect")was found to originate from the enhanced decomposition of strongly adsorbed nitrates on the catalyst surface and the conversion of these adsorbed species to–NCO and–CN species.This"H_(2)effect"occurs in the presence of Ag_(n)^(ᵟ+)species rather than the metallic Ag^(0)species.A gaseous intermediate,acrylonitrile(CH_(2)CHCN),was also identified in the H_(2)/C3H6-SCR reaction using SVUV-PIMS.These findings provide novel insights in the structure-activity relationship and reaction mechanisms of the SA-catalyzed HC-SCR reaction of NO.以烯烃为还原剂的NO_(x)选择性催化还原(HC-SCR)是重要的环境催化反应之一.Ag/Al_(2)O_(3)催化剂(SA)因在HC-SCR反应中表现高活性、高N_(2)选择性及中等H_(2)O和SO_(2)耐受性等优点,而被广泛研究.SA催化剂中存在不同的Ag物种,包括孤立Ag^(+)离子,带部分正电荷Ag_(n)^(δ+)团簇和金属态Ag_(n)^(0)团簇.文献研究结果表明,SA催化剂中Ag_(n)^(δ+)团簇是催化HC-SCR反应的活性Ag物种,而Ag物种类型与Ag的负载量密切相关.因此文献中研究SA催化HC-SCR反应的结构-性能关系主要是通过改变Ag负载量来开展的,最优Ag负载量约为1%~2%.本文以Cl^(–)改性的γ-Al_(2)O_(3)作为载体,采用传统的浸渍法制备了Ag/Al_(2)O_(3)-Cl催化剂(SA-Cl),通过XRD、TEM、H_(2)-TPR、UV-Vis DRS以及XPS对催化剂进行了结构表征,并结合C_(3)H_(6)-SCR和H_(2)/C_(3)H_(6)-SCR活性测试,建立催化剂结构-催化性能关系;同时利用原位傅里叶变换红外光谱(DRIFTS)和在线同步辐射单光子电离质谱(SVUV-PIMS)研究了SA催化HC-SCR的反应机理.结构表征结果表明,在SA催化剂中,Ag负载量的提高主要是增加了Ag_(n)^(0)物种,而在SA-Cl催化剂中,Ag负载量的提高主要是增加了Ag_(n)^(δ+)物种,因此Cl‒改性能促进SA催化剂中Ag_(n)^(δ+)物种的形成.活性测试结果表明,在相同Ag负载量下,SA-Cl催化剂表现出比SA催化剂更好的HC-SCR催化性能.Cl‒改性对SA催化剂中Ag物种的调控作用和HC-SCR催化性能的促进作用随Ag负载量的增加变得更为明显.原位DRIFTS结果表明,γ-Al_(2)O_(3)载体(Al位点)是NO氧化形成硝酸盐物种的主要活性位点;Ag_(n)^(δ+)物种催化丙烯适度氧化主要生成乙酸盐类物种,可以还原表面硝酸盐物种;而Ag_(n)^(0)催化丙烯过度氧化主要生成羧酸盐类物种,进而生成CO_(2),不能还原表面硝酸盐物种.由此可见,Ag_(n)^(δ+)是催化HC-SCR反应的活性Ag物种,而Ag_(n)^(0)是催化烃类完全氧化反应的活性Ag物

关 键 词：In situ characterization Reaction mechanism Structure-activity relation DRIFTS Photoionization mass spectroscopy 

分 类 号：TQ426[化学工程] X701[环境科学与工程—环境工程]