焙烧温度对Au/TiO2催化愈创木酚加氢脱氧反应性能的影响

采用沉积-沉淀法制备了不同焙烧温度的Au/TiO₂系列催化剂，采用TEM、XPS、XRD、N₂吸附-脱附、ICP以及NH₃-TPD等手段表征了Au/TiO₂系列催化剂的物化性能。考察了Au/TiO₂系列催化剂在木质素模型化合物(愈创木酚)加氢脱氧反应中的催化性能，及反应条件对Au/TiO₂-1(焙烧温度为350 ℃)催化愈创木酚加氢脱氧反应性能的影响，并探讨了反应机理。结果表明，当焙烧温度由350 ℃升至650 ℃，Au/TiO2催化剂中Au颗粒平均粒径从2.7 nm增至7.9 nm，晶型保持为锐钛矿型，催化剂比表面积由90 m²/g减至49 m²/g；新鲜和反应后催化剂中的Au均以金属态存在。在愈创木酚加氢脱氧反应中，Au/TiO₂催化剂对酚类产物有很高的选择性。随着催化剂焙烧温度增加，其活性逐渐降低，产物中酚类物质的选择性基本不变；当催化剂上Au颗粒平均粒径小于6 nm时，出现了新的反应路径，即愈创木酚上甲氧基中的甲基加氢生成甲烷。不同反应温度与氢气压力的结果表明，Au/TiO₂催化剂能够高选择性地断裂1个C-O键，而苯环不会被饱和，酚类产物的分布基本没有变化。催化剂重复使用2次性能稳定。

Effects of Calcination Temperature on the Catalytic Activity of Au/TiO2 in Guaiacol Hydrodeoxygenation

A series of Au/ TiO₂ catalysts, calcined at various temperatures, were prepared by deposition-precipitation method, and evaluated by guaiacol (Lignin compound) hydrodeoxygenation reaction. The prepared catalysts were characterized by TEM, XPS, XRD, N ₂ adsorption-desorption, ICP and NH₃-TPD methods. Results reveal that the average particle sizes of Au on the catalysts grow up from 2.7 nm to 7.9 nm along with the calcination temperature increasing from 350 ℃ to 650 ℃. TiO₂ retains in the form of anatase type, accompanied by the decrease of the surface area of the catalysts from 90 m²/g to 49 m²/g. Metallic Au species exist in both the fresh and spent catalysts. The calcination temperatures of Au/ TiO₂ catalysts have negligible effect on the phenolic-product selectivity. When the catalysts with the mean diameter of Au particle size is less than 6 nm, methane is formed from the methoxyl group of guaiacol. The results of different temperature and H₂ pressure highlight that Au/TiO₂ shows high activity to break only one C-O bond of guaiacol, without excessive hydrogenation saturation of π-bond the benzene ring and dissociation of the C=C bond. Furthermore, recycle reactions over Au/ TiO₂ show that the conversion and product yield remain constant during two successive runs, indicating the good recyclability of the catalyst.