Preparation And Applications Of Gold Nano-particles Supported On Different Mesoporous Alumina

Three kinds of mesoporous alumina (denoted as meso-Al₂O₃-x (x =a, b, c)) supports were synthesized by different structure-direct agent and different assembly pathway, respectively. They were used as supports for deposition of nano-gold particles via different methods of homogeneous deposition precipitation (HDP), deposition precipitation (DP) and direct anionic exchange (DAE), respectively. The supported nano-gold samples were characterized by N₂ adsorption, TEM and XPS. The surface basicity of the mesoporous alumina and γ-Al₂O₃ was measured by means of CO₂-TPD. The profiles of CO₂-TPD indicated that the mesoporous alumina owned more abundant surface basic sites than that of the commercial γ-Al₂O₃ and followed the order of meso-Al₂O₃-b > meso-Al₂O₃-c > meso-Al₂O₃-a > γ-Al₂O₃. The TEM observation of the gold-supported catalysts showed the dispersion and average size of the gold particles depended on the number of surface basic sites on the supports. It was found that the gold particles could be uniformly distributed on the support of meso-Al₂O₃-b with more basic sites and the average size of the gold particles was 3.1 nm. The ICP results indicated that the surface basicity of the support has effect on the loading of gold if the Au catalysts prepared at the same condition. The more the number of the surface basic sites on the support posses, the higher of the loading of gold is obtained. The XPS results indicated exclusively Au⁽⁰⁾-particles without any trace of higher oxidized species on the four kinds of Al₂O₃ surface. The surface basicity of the support has no effect on the state of gold if the Au catalysts prepared at the same conditions.The different Al₂O₃ supported Au catalysts were employed as highly active/selective and reusable catalysts for the epoxidation of styrene byanhydrous t-butyl hydroperoxide (TBHP). Among the Au/meso-Al2O3-a, Au/meso-Al2O3-b, Au/meso-Al2O3-c, and Au/y-A12O3 catalysts, the Au/meso-Al2O3-b catalyst showed the best conversion of the styrene due to be smaller size of gold particles deposited on the meso-Al2O3-b. The epoxidation activity of the supported gold catalysts is attributed to the gold species, particularly the low coordinated Au atoms at the corners and edges of nano-size gold particles. The effect of catalysts prepared by different methods and reaction condition on catalytic performances for the epoxidation of styrene are also investigated. The results clearly reveal that the Au/meso-Al2O3-b prepared by the method of HDP shows the best catalytic activity at the temperature of 353 K for 12 h with the TBHP/styrene ratio =1.5.The catalytic activity of the nano-gold catalyst prepared by different methods, the gold loading amounts and the different supports for CO oxidation at low temperature are investigated. The results indicate that the catalytic activity is influenced strongly by the supports. The catalytic activity follows the order of Au/meso-Al2O3-b > Au/meso-Al2O3-c > Au/meso-Al2O3-a > Au/y-Al2O3, which is in good agreement with the order of the number of the surface basic sites on the supports measured by CO2-TPD, the more the number of the basic sites, the better the catalytic activity. The longer life-time of the gold catalyst presented here prepared by the method of HDP is attributed to the retained small Au particles on the support of mesoporous Al2O3-b by HDP. The small Au particles size is advantageous for enhancing and keeping the activity of the supported gold catalysts. The objective of this work was to evaluate the feasibility of reducing carbon monoxide in the mainstream burned from cigarettes by incorporating these catalysts into the filter. It was found that the gold-based catalysts are valuable candidate catalysts for reducing carbon monoxide in mainstream smoke. A new catalyst...