Design of 3-D mesoporous silylated titanosilicate supported gold nanoparticles for direct vapor phase epoxidation of propylene: Role of solid and gaseous promoters

Three dimensional sponglike mesoporous silylated titanosilicate supported gold nanoparticles has recently shown its potential for direct vapor phase epoxidation of propylene using H₂ and O₂ recently. But fast catalyst deactivation and less hydrogen efficiency was the major problem to overcome. In this presentation we focus on the use of very small amount (5-30ppm) trimethylamine as a gaseous promoter for neutralization of acidic by products, which are assumed responsible for catalyst deactivation. The effect of using trimethylamine under different reaction conditions like pretreatment, co feed, was studied. Also the effect of trimethylamine during catalyst regeneration over silylated Ba(NO₃)₂ promoted catalyst was examined thoroughly. Trimethylamine showed very positive effect on the catalyst activity during regeneration improving catalyst life, propylene conversion, and PO selectivity and hydrogen efficiency. Use of trimethylamine on Ba(NO₃)₂ promoted catalyst showed controlled deactivation keeping 75% to 80% of the catalyst activity after 5 hour run. The promoted catalyst was characterized by in-situ UV-Vis-NIR, XPS, and XAFS techniques. Large amount of oxidic gold was found for Ba(NO₃)₂ promoted catalyst which may be responsible for more hydrogen peroxide species formation as found from in-situ UV-Vis spectra. Therefore silylated Ba(NO₃)₂-Au/Ti-SiO₂ (Ti/Si=3/100) will be a real catalyst giving a steady space-time yield for direct propylene epoxidation with molecular H₂ and O₂ in presence of trace amount of trimethylamine (10-20 ppm) in reactant feed mixture.