Supported Vanadia Catalysts with Alkali and Alkaline Earth Additives in Oxidative Dehydrogenation of Propane.Part I.V_2O_5/SiO_2 System

摘要

Alkali(Li,Na,K,Rb)and alkaline earth(Ca,Mg)additives were introduced to vanadia dispersed on silica and the catalysts obtained were characterized by XRD,XPS,isopropanol decomposition(a probe of acido-basic properties),and tested in oxidative dehydrogenation of propane,ODH.V_2O_5 was the main phase observed by XRD.The catalysts showed high concentration of acidic and low of basic centres.The ODH reaction followed a parallel-consecutive route,CO formed consecutively from propene being predominant product of non-selective total oxidation.The presence of the additives led to:a)considerable decrease of the acidity and increase of the basicity,b)decrease of the total activity in ODH,c)increase in the selectivity to propene,the highest effect being observed for K and Rb.The increase in the selectivity to propene on introducing the additives has been ascribed to the decrease in the catalysts' acidity.