Vapor phase propylene epoxidation over Au/Ti-MCM-41 catalysts prepared by different Ti incorporation modes

Ti-containing MCM-41 supports were prepared by: (a) hydrothermal crystallization; (b) post-synthesis grafting; and (c) two-step Ti incorporation-hydrothermal incorporation followed by post-synthesis grafting. XRD revealed little change in crystallinity and long range order of MCM-41 phase after Ti incorporation by different methods. UV-Vis spectra show the presence of tetrahedral Ti sites at lower Ti contents (upto 4.5 mol%), but aggregated titania formation could be observed at higher Ti loadings (>4.5 mol%). The samples exhibit surface areas and pore volumes in the mesoporous range. Vapor phase epoxidation of propene using H-2 and O-2 was carried out over these supports after Au deposition by deposition-precipitation (DP) method. The Ti-MCM-41 supports prepared by two-step Ti incorporation (with up to 4.5 mol% input Ti), which probably have more number of isolated Ti sites, showed higher catalytic activity than Ti-MCM-41 prepared by one-step Ti incorporation method, at comparable propylene oxide selectivities and hydrogen efficiencies. The former catalyst also deactivates more slowly than the latter ones, probably due to a decrease in the number of silanol sites (those responsible for deactivation) due to grafted Ti. (C) 2002 Elsevier Science B.V. All rights reserved.