Selective Catalytic Reduction Of NO_x By Hydrogen Over Modified Pd Catalysts

The harmful effects of nitrogen oxides（NO_x）on human health and the environment are well known,and control technologies for these pollutants have long been a research focus in the field of environmental science.Selective catalytic reduction of NO_xby hydrogen（H₂-SCR）is an environmental benign technology with potential application for the removal of NO_x.In this study,Pd/Ti O₂catalysts were the main research object,and two methods were used to modify its performance:first,a sacrifice carbon layer strategy was used to fabricate Pd/Ti O₂to enhance the Strong Metal-Support Interaction（SMSI）;second,noble metal Ru was further loaded onto Pd/Ti O₂to construct a bimetallic Pd-Ru/Ti O₂catalyst.The physical structure and chemical properties of the catalysts were thoroughly analyzed by multiple characterization methods,and the reaction process and mechanism were analyzed using in situ DRIFTS.The Pd/Ti O₂-D modified by the sacrifice carbon layer strategy showed better catalytic activity than the Pd/Ti O₂catalyst.XPS and high-resolution transmission electron microscopy（HRTEM）results showed that the SMSI was induced on the 0.5Pd/Ti O₂-D catalyst,leading to the smaller catalyst particle size and the generation of more Pd⁰.In situ DRIFTS results showed that the0.5Pd/Ti O₂-D catalyst exhibited the highest adsorption capacity for NO_xin the reaction and the generated NO_xspecies did not disappear even at high temperatures.NH₃species were generated on the Lewis acid sites and they are also reactive,thus effectively promoting the removal of NO_x.For the Pd-Ru/Ti O₂catalyst,the optimal H₂-SCR performance was achieved when the loading of Pd and Ru were 0.5 and 0.1 wt%,respectively（denoted by 0.5Pd0.1Ru/Ti O₂）.This modified catalyst showed significantly higher activity than the 0.5Pd/Ti O₂catalyst,it also exhibited excellent tolerance to impurity gas and good stability.X-ray photoelectron spectroscopy（XPS）combined with hydrogen temperature-programmed reduction（H₂-TPR）characterization results revealed that electron transfer occurred on the catalyst,with electrons transferring from Ru and Ti O₂to Pd to generate Pd⁰,which would promote H₂activation,the content of surface adsorbed oxygen was also increased,which also contribute to the NO_xconversion.In situ DRIFTS results showed that the 0.5Pd0.1Ru/Ti O₂catalyst increased the adsorption strength for NO_xspecies in the reaction and generated NH₃species adsorbed on Lewis acid sites,which assisted the H₂-SCR pathway and enabled highly active and selective conversion of NO_xto N₂via the NH₃-SCR pathway.