The Enhancement For C₃H₆-SCR By H₂ Over Ag-CeZr Catalyst

Nitrogen oxides（NO_x）are the main pollutants causing environmental problems such as acid rain and photochemical smog.The selective catalytic reduction of NO by H₂ and C₃H₆ in denitration technology has great potential because it can effectively improve the low-temperature activity.In this research,the spherical Ag-CeZr catalysts were prepared,the promoting mechanism of H₂ on the reactivity of C₃H₆-SCR was discussed,and the reaction mechanism of H₂-C₃H₆-SCR was proposed.The main research results are as follows:（1）A series of spherical CeZr_x oxide catalysts with different molar ratios of zirconium/cerium were prepared by continuous solvothermal method.CeZr_0.4 had the strongest NO adsorption and activation ability,and generated a large amount of nitrate species.（2）With CeZr_0.4 as the carrier,xAg-CeZr catalysts with different Ag content were prepared by impregnation method.The addition of H₂significantly promoted the low-temperature activity and the N₂ selectivity of C₃H₆-SCR reaction,and widened the reaction temperature window.The NO conversion of 2%Ag-CeZr at 200℃was as high as 71.7%,and N₂ selectivity achieved 45.3%.The physical and chemical characterization results showed that the 2%Ag-CeZr catalyst particles were smaller,with better dispersion,larger specific surface area,and stronger low-temperature reducing ability,so the catalytic activity was higher.（3）In situ FT-IR results showed that H₂ promoted the adsorption and activation capacity of C₃H₆ and NO over xAg-CeZr catalysts,and improved the reactivity of activated species.Based on the migration and transformation of species in the transient reaction,we proposed the reaction mechanism of H₂-C₃H₆-SCR applicable to the xAg-CeZr catalysts at low temperature（200℃）:NO+C₃H₆+H₂+O₂→NO₂^-/NO₃^-+C_xH_yO_z→ONCs→-NCO+-CN→N₂+CO₂+H₂O.It also summarized the role of H₂ in the C₃H₆-SCR reaction,that is,H₂promoted the reaction between C₃H₆ and pre-adsorbed NO adsorption species;H₂ enhanced the activity of the reaction between the C₃H₆preadsorbed species and NO by promoting the pre-adsorption of C₃H₆;adding H₂ to C₃H₆ could still promote the reaction between C₃H₆ and NO+H₂ pre-adsorbed species;adding H₂ to NO would inhibit the reaction between NO and C₃H₆+H₂ pre-adsorbed species.（4）Ag⁺and Ag_n^δ+were the main species on the catalyst surface,and H₂ would promote the reduction of a large amount of Ag⁺to Ag_n^δ+on the surface at low temperature（around 200℃）,thereby promoting the low-temperature activity of the reaction.In the presence of H₂,the loading of Ag would significantly increase the activity of the reaction intermediate on the surface of the catalysts.