Preparation and characterization of porous TiO 2 -SiO 2 mixed oxide
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Preparation and characterization of porous TiO2-SiO2 mixed oxide Ang Thiam Peng*, Zhong Ziyi and James Highfield Applied Catalysis, Institute of Chemical and Engineering Sciences Ltd 1 Pesek Road, Jurong Island, Singapore 627833, Singapore ABSTRACT A study on the comparison of porous TiO2-SiO2 mixed oxides synthesized variously via the “amine directed” method is reported. The amine capping groups were octylamine, dodecylamine, octyldecylamine, aniline, and isobutylamine. The mixed oxide is characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Brunauer-Emmett-Teller analysis (BET). While XRD, SEM and TEM provide mainly (bulk) structural information on the mixed oxide preparations, BET (N2 physisorption) probes into their surface area and texture. IR evidence suggests that intimate chemical mixing of both oxides has occurred, while BET measurements show that high surface areas are attainable and that the mixed oxide is more thermally stable than pure (control) samples of TiO2. INTRODUCTION TiO2 is a stable (wide band-gap semiconductor) photocatalyst for environmental and energy-related applications in both suspended powder and pressed (anode) forms. It is also popular as a support for metals in metal-catalyzed reactions, due in part to its role in “strong metal support interactions”. As with all heterogeneous catalysts, its preparation in thermallystable high-surface-area form, and with good porosity, is beneficial for reactant access and product egress (mass transfer). Interest is growing in developing structures with a substantial level of mesoporosity, since this provides the best compromise between accessible specific surface and diffusional factors. Antonelli and Ying first prepared mesoporous TiO2 using phosphate surfactant as template in 1995 [1]. Unfortunately, it was found that a significant amount of phosphorus was retained even after calcination, such that the product is best described as a titanium oxo-phosphate. More success is now being achieved using alkylamines as templates, or directing agents, in a relatively easy procedure that is growing in popularity. Nonetheless, there remain a number of practical difficulties to be resolved, chiefly the drastic collapse of the precursor structure during calcination (to remove water and the amine template), tentatively linked to phase transformation from the amorphous state into crystalline anatase [2]. Recently, post-treatment with base before the amine removal step has been explored as a possible means to prevent structural collapse [3]. It has also been reported that the catalytic activity and thermal stability of TiO2 can be improved even in mechanical admixture with a suitable amount of SiO2 [4]. Extending this principle, we have attempted to prepare a genuine mixed oxide of TiO2 and SiO2 using octylamine, dodecylamine, octyldecylamine, isobutylamine and aniline as templates. EXPER
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