?-Al₂O₃ Exposing High Energy?111?Facets Prepared By Selective Etching And Its Catalytic Properties

More than 90%of the production process of man-made chemicals involves catalytic technology,and heterogeneous catalytic technology becomes the mainstream with the advantage of easy separation between catalysts and products.Almost all heterogeneous catalysis processes take place on the surface of the catalyst.Therefore,the surface structure of the catalyst significantly affects its catalytic performance.With the development of nanomaterial synthesis technology,we can design and synthesize the catalyst or catalyst supports exposing the specific crystal surface,thus significantly improving the performance of the traditional catalyst.In our previous research work,the ?-Al2O3 exposing(111)crystal surface was prepared by the bottom-up assembly method.From the DFT calculation and experimental characterization,the principle of the preparation method and new properties of the?-Al2O3 exposing(111)crystal surface are revealed.However the preparation method used previously is too cumbersome and difficult to enlarge.Now the top-down etching method is adopted to prepare the ?-A12O3 exposing(111)crystal surface.This operation method is simple and easy to enlarge,and the products produced are quality reliable.Besides the effects of the obtained alumina as the catalyst and catalyst support in different catalytic reactions are systematically studied.The main contents are as follows:The alumina which exposing(111)crystal surface is prepared by etching method while oleic acid is used as the crystal surface protection agent and ammonia as etchant.The effects of the concentration of ammonia,the temperature and time of the hydrothermal treatment are systematically studied.The prepared sample is characterized by the BET and D2-OH isotope heat-driven exchange spectrum and compared with the sample obtained by the assembly method.It is confirmed that the?-Al2O3 with the(111)crystal plane can also be obtained by etching method.The role of gamma alumina exposing on different crystal facet played in the catalytic reaction as the main catalyst and catalyst support is investigated.The alumina exposing on(111)crystal facet shows superiorer catalytic activity in the methanol dehydration reaction,isopropanol dehydration reaction and furfural selective hydrogen reaction as the main catalyst than the alumina commercial.As catalyst support,it also shows superiorer catalytic activity when supported Pd in the phenylacetylene selective hydrogenation reaction and supported Co3O4 in the CO oxidation reaction.These results show that the different crystal surface of gamma alumina have different effects on the metal and metal oxide and further evidence that this top-down etching method can actually produce gamma alumina exposing on high energy crystal surface.The effect of reduction oxidation process of the Co3O4/Al2O3 catalyst on CO oxidation is studied.It is found that the catalytic activity of the catalyst is significantly enhanced after the reduction oxidation pretreatment.The surface reconstruction occurred during the reduction oxidation pretreatment accounting for the improvement of the catalytic activity which further indicates the influence of the surface structure on the catalytic performance of the catalyst.