Preparation and properties of TiO2 / SBA-15 supported gold catalyst

• Main Authors: Chieh-Chuan Su, 蘇玠銓
• Other Authors: Tuan-Chi Liu
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/03570006940772493007

碩士 === 國立臺灣科技大學 === 化學工程系 === 102 === The high oxidative activity of gold catalysts at low temperature has attracted many interests lately. Au / TiO2 is one of the catalysts with the most attention. However, this catalyst suffers from inadequate mechanical strength and low surface area due mostly to its support TiO2. In this study, an attempt was made to improve the situation by coating TiO2 onto the surface of SBA-15, a high surface area mesoporous molecular sieve, to create a new material, TiO2 / SBA-15, with a high TiO2 surface area and a sound mechanical strength. Gold catalysts were then prepared using this new material as support. To understand the loading effects, TiO2 / SBA-15 of varied TiO2 contents, done by repeat impregnation, were prepared. Each impregnation increased the TiO2 by 10 wt %. Thus three supports, S15-Ti-10, S15-Ti-20 and S15-Ti-30, were obtained. In naming them, S15 designated for SBA-15, Ti for TiO2, and the number after Ti for the wt % of TiO2. The supports were then used to prepare Au / S15-Ti-10, Au / S15-Ti-20 and Au / S15-Ti-30, the gold catalysts, via deposition precipitation. Each catalyst was loaded with 1 wt % gold. Two other catalysts, Au / SBA-15 and Au/TiO2, were also prepared for comparison purpose. The catalytic properties of the catalysts were characterized by powder X-ray diffraction (PXRD), small angle X-ray diffraction (SAXRD), N2 adsorption (BET and pore size), transmission electronic microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and temperature programmed desorption of CO and O2 (CO-TPD and O2-TPD). The activity of the catalysts was investigated by CO oxidation at 1 atm and 25-125oC. The reaction system consisted a micro-reactor made of pyrex glass. The feed flew continuously through the catalyst bed. The concentration of CO in the feed was 100 ppm in air. The stability of the catalysts was tested at 120oC for 8 hours. The results showed that the precursor of TiO2, Ti(OCH(CH3)2)4, could successfully be delivered inside the pores of SBA-15 where it decomposed upon calcination and then attached to the walls. The TiO2 appeared to be highly dispersed and amorphous. The thickness of the attached TiO2 layer increased with repeat impregnation. The TiO2 molecules were bound by Ti-O-Ti bonds, and Ti-O-Si bonds were formed on the interface of TiO2 and SBA-15. TiO2 / SBA-15 possessed ordered- mesoporous pores similar to those of SBA-15, but with smaller pore volume and pore diameter. The volume and diameter became even smaller with an increase in TiO2 loading. The surface area of TiO2 / SBA-15 neared that of SBA-15, which was significantly larger than that of TiO2. The surface properties of TiO2 / SBA-15 shifted toward those of TiO2 with an increased TiO2 loading, and nearly identical to those of TiO2 when the loading reached 30 wt %. The activity and stability of the catalysts increased with a decrease in the size of gold particles. The size was in the order: Au/SBA-15 > Au / S15-Ti-10 > Au / S15-Ti-20 > Au / TiO2 > Au / S15-Ti-30。The size on Au / S15-Ti-30 was the smallest which meant catalysts with higher activity and stability than conventional Au / TiO2 could be prepared using TiO2/SBA-15 as a support.