【摘要】 利用ＥＰＲ等谱学方法，对Ｗ／ＨＺＳＭ－５基催化剂上Ｗ物种的价态及其在Ｈ２预还原过程中的动态行为进行了表征研究．结果表明，由碱性前驱液制备的Ｗ／ＨＺＳＭ５催化剂在１０７３Ｋ、Ｈ２预还原条件下只能还原产生一类主要Ｗ物种，Ｗ５＋；而由酸性前驱液制备的Ｗ－Ｈ２ＳＯ４／ＨＺＳＭ－５催化剂在相同反应条件下则可还原产生两类共存的Ｗ物种，Ｗ５＋和Ｗ４＋．关联到在相同的甲烷脱氢芳构化（ＤＨＡＭ）反应条件下Ｗ－Ｈ２ＳＯ４／ＨＺＳＭ－５对ＤＨＡＭ反应的催化活性比Ｗ／ＨＺＳＭ－５高得多的实验事实，可以推断，ＤＨＡＭ反应活性与催化剂上较高价态Ｗ物种（Ｗ５＋）的浓度并不存在顺变关系，而与Ｗ４＋物种的浓度则密切相关．更多还原

【Abstract】 By using EPR method, valence states of the W species in the W/HZSM 5 based catalysts and their dynamic behavior during the process of hydrogen prereduction have been characterized. The taken EPR spectra showed that the H 2 reduction of the W/HZSM 5 catalyst, prepared from an alkaline solution of (NH 4) 2WO 4(pH=8～9), at 1 073 K for 30 mins produced mainly only one type of W 5+ species with a strong EPR signal ( g ∥ =1.82 , g ⊥= 1.95 ) and the intensity of this signal did not weaken with prolonging time for the reduction, indicating that the further reduction of this type of W 5+ species was quite difficult, and that the H 2 reduction of the W H 2SO 4/HZSM 5, prepared from an acidified solution of (NH 4) 2WO 4 (pH=2～3), at the same conditions produced two type of W 5+ species with two EPR signals corresponding to g ∥ (1) =1.82, g ⊥ (1) =1.95 and g ∥ (2) =1.88, g ⊥ (2) =1.97, respectively, and the intensity of the latter EPR signal weakened greatly with time for the reduction prolonged to 60 mins, implying that a considerable proportion of the second type of W 5+ species was further reduced to W 4+ valence state of EPR silence. In correlating to the experimental fact that activity of the dehydro aromatization of methane (DHAM) over the W H 2SO 4/HZSM 5 was much higher than that over the W/HZSM 5, it could be inferred that the observed high DHAM activity was not proportionally related with the concentration of the W 5+ sites, and , rather, closely related with that of the W 4+ sites at the surface of the functioning catalysts.更多还原