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On Effective Locations of Catalytic Active Sites in Phase Boundary Catalyst
Hadi Nur1, Nur Hidayah Mohd Ran1, Nursyafreena Attan1, Shigeru Ikeda2 & Bunsho Ohtani3
1Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia
2Research Center for Solar Energy Chemistry, Osaka University, 1-3 Machikaneyama, Toyonaka 560-8531, Japan
3Catalysis Research Center, Hokkaido University, Sapporo 001-0021, Japan
Abstract. Zeolite loaded with alkylsilane-covered titanium oxide was found to be more effective than nonporous silica counterpart as “phase-boundary catalyst (PBC)” to promote the epoxidation of alkenes with aqueous hydrogen peroxide. It was demonstrated that the phase-boundary catalyst system required neither stirring to make an emulsion nor addition of a cosolvent to make a homogeneous solution to drive the reaction. However, some basic facts about them remain unclear, such as the question as to where an effective location of the active sites of PBC: is it the external surface of the catalysts or in their pore? In order to elucidate this problem, TS-1, HZSM-5 and zeolite loaded with alkylsilane–covered sulfonic acid in which the location of the active sites mainly inside the pore system are chosen as model catalysts. Catalytic activity of TS-1 and HZSM-5 catalysts were examined after modification with n-octadecyltrichlorosilane (ODS). Their activities are compared with zeolite loaded with alkylsilane-covered titanium oxide particles, in which the active sites are on their external surface in reactions of 1-octene with aqueous H2O2 and cyclohexene with water as model reactions. It was suggested that the location of the active sites on the external surface plays an important role in ”phase-boundary catalysis” phenomenon.
Keywords: location of catalytic active sites; phase-boundary catalysis.