Mo/HZSM-5基甲烷非氧化脱氢芳构化催化剂的TPD及TPR研究

TPD and TPR Characterizations of Mo/HZSM_5based Catalysts for Non-oxidative Dehydro-Aromatization of Methane

在Ｍｏ／ＨＺＳＭ－５基甲烷非氧化脱氢芳构化催化剂中加入促进剂ＺｎＳＯ４，使该催化剂的活性和操作稳定性大为改善．对非促进的Ｍｏ／ＨＺＳＭ－５和促进型的Ｍｏ－ＺｎＳＯ４／ＨＺＳＭ－５甲烷芳构化催化剂的ＮＨ３－ＴＰＤ研究结果表明，促进剂ＺｎＳＯ４的加入大大提高了催化剂表面的Ｂ－酸位浓度；这种Ｂ－酸位能较稳定地存在于催化剂表面，不易流失；催化剂表面高浓度Ｂ－酸位的稳定存在是其甲烷非氧化脱氢催化活性显著提高的关键因素．Ｈ２－ＴＰＲ结果显示，过高的焙烧温度不仅不利于维持催化剂的表面酸性位（尤其是Ｂ－酸位）的浓度，还可能导致催化剂表面Ｍｏ物种的聚集和ＭｏＯ３微晶的生成，使同一Ｍｏ负载量的催化剂中可还原至较低价态的Ｍｏ物种所占比例下降．

Addition of a promoter ZnSO_4 to a Mo/HZSM_5 catalyst for nonoxidative dehydroaromatization of methane has been found to markedly enhance the activity of methane conversion over the catalyst. The result of the TPD testing of NH_3 adsorbed on the catalyst MoZnSO_4/HZSM_5 indicated that the addition of ZnSO_4 promoter resulted not only in an increase in concentration of Bacidic sites at the catalyst surface, but also in making these acidic sites more stabilized and uneasily to lose, which were most probably the main reason for the enhancement of the activity of methane conversion over the catalysts. The results of the H_2TPR showed that unapt high calcination temperature in the preparation of catalyst would not only lead to loss of the Bacid sites, but also bring about aggregation of Mocontaining species and formation of MoO_3 crystallites at the surface of the catalysts; the latter would lead to decreasing in the amount of Mocontaining species reducible to lower valence state(s) at the catalyst surface. 