利用TPD-MS、IR和XPS表征还原态Co-Mo/Al2O3

本文利用NO或/和CO吸附的TPD-MS方法, 结合IR和XPS对还原态的Co, Mo, Co-Mo/Al_2O_3催化剂进行了深入考索. 结果表明, 还原态的Co-Mo/Al_20_3表面上存在着两种吸附NO的Mo中心. 弱吸附NO(T_(max)为100 ℃)可被吸附的CO取代和强吸附NO(T_(max)为300 ℃)不能被CO取代. 同时存在三种吸附NO的CO中心, T_(max)分别为80 ℃、180 ℃和330 ℃. 前两者能吸附CO, 后者只吸附NO. IR结果对这些不同的Mo中心和Co中心的存在提供了进一步旁证. XPS结果表明提高还原温度, Mo/Al比保持恒定, 但Mo~(4+)浓度增加, 而Co/Al比却因部分Co进入Al_2O_3体相而降低。

Characterization of Reduced State of Co-Mo/Al2O3 by TPD-MS、IR and XPS

CO or/and NO co-adsorption on reduced Co/Al_2O_3, Mo/Al_2O_3 and Co-Mo/Al_2O_3 was studied by TPD-MS, IR and XPS. It was found that there exist two kinds of Mo-sites and three kinds of Co-sites on reduced Co-Mo/Al_2O_3. For Mo--sites, One is a weaker adsorption NO (T_(max): 100 ℃) which can be replaced by adsorption CO another is a stronger adsorption NO (T_(max): 300 ℃) which is not replaced by CO. Three kinds of Co--sites for NO adsorption emerged desorption peaks of NO at 80 ℃, 180 ℃ and 330 ℃ respectively. Former two can adsorb CO however, the latter only adsrb NO and all CO adsorbed on Co—sites can be replaced by co-adsorptoin NO.Results of IR provided further evidence about existence of various Mo—sites and Co—sites. Results of XPS indicate that ratio of total Mo/Al is constant, but relative density of Mo~(4+) increase with reduction temperature. While ratio of Co/Al decrease due to Co on surface introduced in bulk phase of Al_2O_3 when reduction temperature raised. In this work it was not observed the existence of direct interaction between Co—sites and Mo—sites, which results in change of property relative to adsorption of CO and/or NO on Co—sites and/or Mo—sitews in the range of reduction temperature from 400 to 600 ℃.