| With the acceleration of industrialization and urbanization in China,more attention has been paid to the environment protection to counter for the climate change.As the government published the new policy named "The National Sixth Stage Motor Vehicle Pollutant Emission Standard",the automobile exhaust treatment industry will meet a great opportunity,especially for the elimination of CO and NO exhaust.The development of green and economic catalysts is urgently needed.Because of the limitation of characterization methods,it is still far not enough in understanding the physical and chemical changes of catalysts during the reaction process.With the development of in-situ characterization technology,it is possible for us to more thoroughly realize the surface dynamic changes of the catalysts during the reaction and distinguish the active center.This is pretty significant for the design and optimization of novel catalysts.In this thesis,Cu(111),Pd/Cu(111)alloy and TiOx/Cu(110)surfaces were adopted as model catalysts surfaces.Combining surface science research methods and in-situ IRAS,we studied the dynamic changes of the catalyst surfaces and identify the reactive components at the molecule-atomic level.The main research results are listed as follows:1.We investigated the dynamic changes of the Cu(111)surface under CO+O2 reaction conditions and studied the relationship between different surface species and the catalytic activity.The results showed that the Cu(111)surface can be directly oxidized to Cu2O by O2 at room temperature but further oxidized to CuO requiring at a higher temperature.After the Cu(111)surface was exposed to CO and O2,there were two infrared spectral peaks at 2113 cm-1 and 2149 cm-1 which could be attributed to the(O)Cuδ+-CO(0<δ<1)species.We further studied the CO oxidation reaction by in-situ IRAS,which offers to obtain information of the surface species,changes of the surface,and the product formation during reaction in one spectrum.We found that Cu2O can also form on the surface at a pressure ratio of O2:CO=1:10.When at a high O2 partial pressure(O2:CO=2:1),no CuO formed on the surface even at 623 K,where Cuδ+ and Cu2O coexisted.We combined temperature-programming reaction with infrared spectroscopy to compare the activity of Cu(111)and Cu2O/Cu(111),and found that the activity of each species followed the order of Cu+>Cuδ+.2.Then,we deposited Pd atoms on the Cu(111)surface and established the Pd/Cu(111)alloy surface.In-situ IRAS,AES and LEED were performed to investigate the dynamic surface and catalytic performance of Pd/Cu(111)alloy surface for CO+O2 reaction.The results showed that Pd segregated to the outermost layer after exposing to CO at 300-573 K,while Cu2O and Cuδ+ formed on the surface and Pd migrated to the near surface layer when further exposed to O2.We further found Cu2O and Cuδ+ coexisted on the surfaces,and Pd migrated to the near surface layer with Cu2O dominating on the surface in both oxygen-poor and oxygen-rich during CO oxidation reaction.The catalytic activity for CO oxidation on Cu2O-Pd/Cu(111)formed by Pd/Cu(111)was higher than Cu2O/Cu(111)formed by Cu(111),indicating that Pd should locate in Cu2O near the surface region to promote the reaction.3.Well-defined TiOx films in a layer-by-layer growth mode were grown on the Cu(110)surface by a reactive evaporation method.The monolayer represents a hexagonal structure of CuTiOx mixed oxide films with single-site Cu+(-O-Ti-).The films were stable enough under vacuum below 873 K,but the bilayer was less stable.The Cu+(-O-Ti-)was stable and anti-reducible by CO,and could be completely reduced at 673 K,indicating that CuTiOx mixed oxide can stabilized Cu+(-O-Ti-).Under the CO+NO reaction conditions,the Cu2O on Cu2O/Cu(110)films was unstable and reduced,but the Cu+(-O-Ti-)of TiOx/Cu(110)was stable.Compared to the Cu(110),but the overall catalytic activity is slightly lower on the TiOx/Cu(110)films surface,indicating single-atom Cu+(-O-Ti-)site is less efficient for CO+NO reaction. |
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