Researches Into The Activity And Hydrothermal Stability Of Rh-based Three-way Catalysts

Rh has been frequently used in three-way catalysts because of its extraordinary activity in the catalytic reduction of NO_x.However,under the high-temperature hydrothermal environment during real driving conditions,Rh-based catalysts might suffer from severe activity loss due to the strong metal-support interaction between Rh and catalyst supports.As a result,understanding and thus controlling the metal-support interaction,are of great importance in the rational design and practical use of Rh-based three-way catalysts.In this work,the influence of Ce/Zr ratio on the activity and high-temperature hydrothermal stability of Rh/Ce_xZr_1-xO₂（x=0,0.05,0.3,0.5）catalysts was investigated.It was found that the activities and high-temperature hydrothermal stabilities of Rh/Ce_xZr_1-xO₂（x=0,0.05,0.3,0.5）catalysts decreased with the increase of Ce content,among which the Ce-free catalyst,Rh/ZrO₂,exhibited the optimal performance.The introduction of cerium tends to deactivate the Rh/Ce_xZr_1-xO₂ catalysts due to the strong Rh-O-Ce interaction,leading to the formation of a new but less reactive Rh site（Siteβ）on the surface of the support.The strong Rh-O-Ce interaction also induces the migration of Rh species into the bulk of Ce_xZr_1-xO₂ support during the hydrothermal aging at 1050℃ for 12 h,exacerbating the inferior activities of Ce-rich catalysts.On the Rh/ZrO₂ sample,the surface agglomeration of Rh species also leads to the deactivation of the aged catalysts during hydrothermal aging,but the extent is much lighter than that of the Ce-containing Rh/Ce_xZr_1-xO₂ samples.The effect of Zr introduction on the high-temperature hydrothermal stability of Rh/Al₂O₃ catalyst was also investigated.After the introduction of Zr into the Rh/Al₂O₃catalyst system,the Rh-Al₂O₃ interaction would be controlled,decreasing the extent that Rh migrated into the bulk of Al₂O₃ support.Thus,the high-temperature hydrothermal stability of Rh/Al₂O₃ catalyst is improved.This work enables readers to get more knowledge about the metal-support interaction in Rh/Ce_xZr_1-xO₂ and Rh/Al₂O₃ catalysts.In the meantime,it can also provide some theoretical guidance to the rational design and practical use of three-way catalysts.