TiO_2改性银铝催化剂选择性丙烯还原NO_x硫失活机制研究

Deactivation of TiO_2-modified Ag/Al_2O_3 catalyst by SO_2 in the reduction of NOx by propene

采用溶胶凝胶法制备4%Ag/Al2O3、4%Ag/10%TiO2-Al2O3催化剂.利用N2物理吸附、氮氧化物/二氧化硫程序升温脱附(NOx/SO2-TPD)以及普通/原位漫反射傅里叶变换红外光谱(FT-IR/DRIFTs)对催化剂进行表征,并探讨催化剂在含硫气氛前后选择性还原NOx活性的变化及中毒机理.结果表明在4%Ag/Al2O3催化剂中掺杂10%TiO2能提高催化剂的中低温活性以及在400℃下抗SO2中毒的能力.TiO2引入后可促进甲酸盐物种的形成从而有利于低温反应的进行;SO2与NO在同一活性位上出现的竞争吸附以及活性组分Ag的硫酸化是4%Ag/Al2O3催化剂失活的重要原因;TiO2的加入能促进NO在催化剂表面的吸附并能减弱其对SO2的吸附,同时能有效抑制活性组分Ag的硫酸化,从而提高催化剂的抗硫性.

Ag-base catalysts supported on Al2O3 and TiO2-Al2O3（the mass ratio of TiO2 to Al2O3 was 1：10） were prepared by sol-get method respectively.The catalysts were characterized by N2 physisorption,NOx/SO2-TPD,FT-IR and DRIFTs measurements.The effect of SO2 on the selective reduction of NOx by propene over the catalysts and the poisoning mechanism were investigated.The results showed that the catalytic activities under the low-medium temperature and the resistance of sulfur poisoning at 400 ℃ were enhanced after addition of 10% TiO2.The formation of formate resulted from the introduction of TiO2 was in favor of the reaction at low temperature,and the competitive adsorption of NO and SO2 and the formation of silver sulfate were proved to be the main reason for deactivation of 4%Ag/Al2O3 catalyst.The addition of TiO2 could not only improve the adsorption of NO and inhibit the adsorption of SO2 on catalyst surface,but also inhibit the sulfation of Ag during the catalytic process,which could enhance sulfur poisoning performance of the catalysts eventually.