Liquid-gas boundary catalysis by gold/polystyrene-coated hollow titania and the effective location of active sites in liquid-liquid phase-boundary catalyst

The research described in this thesis is an attempt to synthesize floating catalyst to be used in phase-boundary catalysis for liquid-gas reaction. It is also an attempt to determine the effective location of catalytic active sites in phase-boundary catalyst for immiscible liquid-liquid reaction. Phase-boundary catalysis (PBC) is a heterogeneous catalytic reaction in which the catalyst particles are located at the interphase of either immiscible liquid-liquid or liquid-gas phases. In this research, gold/polystyrene-coated hollow titania was successfully synthesized. The synthesis steps involved hydrothermal synthesis of carbon sphere from sucrose as the template, coating of the carbon sphere with titania, removal of the carbon sphere to produce hollow titania, followed by coating of polystyrene on the surface of hollow titania and the attachment of gold nanoparticles. The results showed that the size of the carbon spheres increased when the concentration of the sucrose increased. The hollow titania obtained by carbon sphere template was found to have smaller diameter than its template and was in the anatase phase. Polystyrene was coated on hollow titania by in-situ polymerization of styrene with aqueous H2O2, while gold was deposited by sputtering deposition technique on the surface of polystyrene-coated hollow titania. It has been demonstrated that gold/polystyrene-coated hollow titania can float on water due to its low density and it is a potential catalyst for liquid–gas boundary catalysis in the oxidation of benzyl alcohol by using molecular oxygen. In this study, some aspects in the determination of the effective location of active sites of PBC in immiscible liquid-liquid system were also studied using NaY, HZSM-5 and TS-1 zeolites as the catalysts in the oxidation of 1-octene and hydroxylation of cyclohexene using aqueous H2O2. Based on experimental results, it is concluded that the effective location of active sites is located on the external surface of zeolites

On Effective Locations of Catalytic Active Sites in Phase Boundary Catalysts

Zeolite loaded with alkylsilane-covered titanium oxide was found to be more effective than its nonporous silica counterpart as phase-boundary catalyst (PBC) to promote 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 resides: is it on the external surface of the catalysts, or in their pores? 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 is mainly inside the pore system, were chosen as model catalysts. Catalytic activities of the catalysts TS-1 and HZSM-5 were examined after modification with n-octadecyltrichlorosilane (ODS). Their activities were compared with zeolite loaded with alkysilane-covered titanium oxide particles, in which the active sites are on the external surface in reactions of 1-octene with aqueous H2O2 and cyclohexene with water as model reactions. The study suggests that the location of the active sites on the external surface plays an important role in the phenomenon of phase-boundary catalysis

On effective locations of catalytic active sites in phase boundary catalysts

Zeolite loaded with alkylsilane-covered titanium oxide was found to be more effective than its nonporous silica counterpart as phase-boundary catalyst (PBC) to promote 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 resides: is it on the external surface of the catalysts, or in their pores? 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 is mainly inside the pore system, were chosen as model catalysts. Catalytic activities of the catalysts TS-1 and HZSM-5 were examined after modification with n-octadecyltrichlorosilane (ODS). Their activities were compared with zeolite loaded with alkysilane-covered titanium oxide particles, in which the active sites are on the external surface in reactions of 1-octene with aqueous H2O2 and cyclohexene with water as model reactions. The study suggests that the location of the active sites on the external surface plays an important role in the phenomenon of phase-boundary catalysis