Multiple Surface Active Sites Of Ceo₂ And Their Cooperative Catalysis

Cerium Oxide?CeO₂?,containing three surface active sites:redox sites,Lewis acidic sites and Lewis basic sites,is a multifunctional catalyst and has been widely applied in the field of catalysis.At present,the spatial distance and structural relationship between Lewis acid-base sites and redox sites on the surface of CeO₂ catalyst are still unclear.In order to explore the spatial relationship between various active sites on the surface of CeO₂ and their correlation of catalytic activities,we studied various surface active sites of CeO₂ through capping experiment,methanol-pyridine co-adsorption Infrared Spectroscopy and Density functional theory?DFT?calculation.The main results presented in the dissertation have been summarized as follows:1.The capping experiments were carried out with DMF?or DMSO?,pyridine,benzoic acid as capping reagents for redox sites,Lewis acid sites and Lewis bases site of CeO₂,respectively.Oxidative coupling of aniline and benzyl alcohol,the transamidation of aniline/benzylamine in the presence of DMF,oxidation of benzyl alcohol,and hydrolysis of 1,3-dioxane were selected as probe reactions.It turns out that the three active sites on the surface of CeO₂ work independently in the catalytic reactions.Capping one of the actives did not affect the activity of the other two active sites.2.Oxidative coupling of benzyl alcohol and aniline was employed as a probe reaction for the investigation of the spatial distance relationship between redox sites and Lewis acid sites of CeO₂.The addition of 2-cyanopyridine as a capping reagent inhibited the reaction.It is known that pyridinic nitrogen of 2-cyanopyridine could be adsorbed strongly to Lewis acid and cyano group could be adsorbed on the redox site,thus it could be concluded that the redox sites and Lewis acid on of CeO₂ are close to the each other.3.Methanol and pyridine were selected as probe molecules to conduct Infrared adsorption experiments of CeO₂.The results further confirm that the spatial positions of Lewis acid sites and redox sites of CeO₂ are mutually independent.4.The adsorption states and energies of the capping agents inducing DMSO,DMF,benzoic acid,and pyridine of the CeO₂?111?were studied using DFT calculations.It was found that DMSO and DMF absorb on CeO₂ via the coordination of O atom to the oxygen vacancy.Benzoic acid is dissociatively adsorbed and H atom adsorbs on the O atom of CeO₂.Pyridine adsorbs on the CeO₂ surface through the coordination of the pyridinic nitrogen to the Ce atom near the oxygen vacancy.These theory results are in accordance to the experiment phenomena and reveal the multi active sites in CeO₂ and their spatial relationship.