丙烷氧化脱氢不同硅基载体负载钒氧化物催化剂的TPSR表征

研究了钒负载不同氧化硅载体(Silica-gel,SBA-15,MCM-41,fumed-SiO2,Nano-SiO2)的丙烷氧化脱氢(ODH)催化剂的结构特征和催化性能,结合催化剂的程序升温表面反应(TPSR)的差热热重质谱(TG-DSC-MS)和原位紫外漫反射光谱(UV-vis DRS)等技术,研究钒在载体上的分散度和晶格氧的反应性。结果表明:负载型钒氧化物催化剂的活性取决于钒在不同硅基载体上的分散度,高度分散的隔离的四配位V5+是丙烷氧化脱氢的活性位。C3H6选择性主要与催化剂的平均孔径相关联,平均孔径越小,产物C3H6越易发生深度氧化。另外,不同氧化硅载体晶格氧与钒的结合强度对C3H6的选择性也产生影响,结合力较弱的V-O-Si中的晶格氧是丙烷氧化脱氢的燃烧位,且燃烧温度随晶格氧与钒、硅结合强度的减小而降低。而与钒结合力较强的V=O和V-O-V中的晶格氧是丙烷氧化脱氢的选择氧化位。硅基载体形貌和结构的不同导致负载型钒氧化物催化剂丙烷氧化脱氢活性和选择性发生差异。

TPSR Characterization of Vanadia Catalysts Supported on Different Structure Silicas for Propane Oxidation Dehydrogenation

The structural characteristics and the performance of vanadia catalysts supported on Silica-gel, SBA-15, MCM-41, fumed-SiO₂, Nano-SiO₂ in oxidative dehydrogenation(ODH) of propane have been investigated. Vanadia dispersion on supports and reactivities of the lattice oxygens have been studied using TG-DSC-MS of temperature-programmed surface reaction(TPSR) and in-situ ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) techniques.It has been shown that the reactivities of supported vanadia catalysts for ODH of propane are mainly attributed to the high degree of vanadia dispersion , high dispersed isolated tetrahedred V⁵⁺ species are the active sites for ODH of propane. The selectivities of C₃H₆ are relative to the average pore diameter of catalysts, The small pore diameter causes the deep oxidation of C₃H₆ easily.The bond strength between vadadium and the lattice oxygen on different silica supports influences on the selectivity of C₃H₆. The weak lattice oxygens of V-O-Si are the combustion site, and the combustion temperature decreases with the reducing of the bond strength. However, the strong bound lattice oxygens of V=O and V-O-V are the site of the selective oxydehydrogenation of propane. The differences of shape and structure on silica supports give rise to the different activities and selectivities for ODH of propane over supported vanadia catalysts.