Investigation Of V-Ce Interaction And Active Sites Of The VO_x/CeO₂ Catalysts For NH₃-SCR Reaction

Nitrogen oxides are the main cause of atmospheric pollution events such as haze,photochemical smog and ozone.NH₃-SCR technology is one of the important means to effectively remove NO_x,and its core is the development of high-performance SCR catalyst.At present,the traditional VWTi catalyst has problems such as narrow active temperature window and low N₂ selectivity at high temperature,so the research on efficient SCR catalyst has always been a hot spot in the international catalysis field.VO_x/CeO₂catalysts have outstanding redox properties and stongher acidic sites,which can significantly promote the NH₃-SCR reaction.However,there is no unified conclusion about the active sites of the catalyst and its reaction mechanism.Taking VO_x/CeO₂ catalyst as the research object,a series of samples with different existence states of V species were obtained by changing the load content of V species.Research shows that:V species were highly dispersed on the surface of cerium oxide at 1% V load.When the load of V species increased to 3%,the V-O-Ce bridge modes and oligomer VO_x were formed under the surface of the carrier.When the V species increased to 6%,not only V-O-Ce bridge modes and oligomer VO_x,but also trace amount of CeVO₄ were generated.The vanadium loading affects the vanadia species on the surface of the catalysts and its catalytic performance.V-O-Ce bridging modes sigficantly affect the NH₃-SCR activity.By controlling the specific surface area of the carrier CeO₂,series VO_x/CeO₂samples with different carrier properties were obtained.The study showed that when the V species were dispersed on the surface of cerium oxide with different specific surface areas,the V-O-Ce bridge modes and the oligomer VO_x content were different,and the more the former was generated,the better the catalytic reduction performance and the stronger the acid potential of the VO_x/CeO₂ samples.Kinetic experiments and TOF values showed that the V-O-Ce bridge modes are the active sites of SCR reaction.Titration experiments showed that NH₃ species played an important role in adsorption and activation on the catalyst surface,and the reaction process followed the eley-ridal reaction mechanism.