Gas-phase synthesis,sructure and sruface acid-base properties of highlydispersed vanadia/titania/silica catalysts.

摘要

the atomic layer deposition(ALD) method based on surface-saturating gas-solid reactions was applied to grow vnadia species on highly dispersed titania/silica supports withfor submono- to above monolayer levels of titania.The physicochemical properties of the V_2O_5/TiO_2/SiO_2 catalysts were examined with N_2 adsorption,XRD,XPS and Raman spectroscopy techniques.The catalysts were compared to thecorresponding titania supported catalysts,and besides a series of liquid-phase impregnated samples were characterized for comparison.In the ALD catalysfts,and besidesa series f liquid-phase impregnatd samples were characterized fro comparison.In the ALD catalysts,isolated and highly dispersed tetrancoordinated VO_x species were formed on titania/silica supports withonly small impact on the surface area an porosity of the support.Vanadia was homogeneously associated with both the surface titania species and the uncovered silica support.However,in theimpregnated catalysts,crystalline vanadia at low titania coverage and TiO_x agglomeration at high titania level decreased the surface area.Vanadia had also a preferential interaction with the titania phase.Moreover,the better dispersion of the active species in the ALD catalysts was confirmed by XPS ofNH_3 adsorption and microcalorimetry of NH_3 and SO_3 adsorption.The number and strength of acid-base sites on the surface of the catalysts wer directly related t the V-O-Ti and V-O-Si concentrations as well as to the titania and vanadia dispersion in the samples,in favor of the ALD catalysts.