Catalytic Oxidation of Styrene to Prepare Benzaldehyde over TiO_2/SiO_2

In the oxidation of styrene by oxygen(in air) over TiO2/SiO2 catalysts,benzaldehyde and formaldehyde were formed as the major products.The reaction could be carried out below 100 ℃.High benzaldehyde selectivity(95.0%) was obtained at relatively lower styrene conversion(18.0%).The investigation indicates that the styrene conversion increased with the increase of TiO2 concentration in TiO2/SiO2 catalysts,but the benzaldehyde selectivity decreased with the increase of TiO2 concentration.The addition of toluene in styrene influenced the styrene conversion and benzaldehyde selectivity.When a toluene-styrene solution containing 20%(in volume) of toluene was used as the reactant feeding,an optimum reaction result was obtained.The flow of air also influences the reaction.However,when the space velocity of air is higher than 571 mL/g·h,the space velocity of air does not influence the styrene conversion and benzaldehyde selectivity anymore.In the reaction,when the flow of liquid(styrene plus toluene) increases,the conversion of styrene decreases and the selectivity of benzaldehyde increases.When catalysts have different TiO2 concentrations,the conversion of styrene increased with the increase of TiO2 and in this case,the specific surface areas of catalysts are only the secondary factor that influences the styrene conversion.However,when catalysts have the same composition,but have different specific surface areas,the specific surface area become the most sensitive factor,which impacts the reaction.Higher specific surface area corresponds higher styrene conversion.