【摘要】 由Ｈ２ＳＯ４酸化的（ＮＨ４）２ＷＯ４溶液（ｐＨ＝２～３）制备的ＷＨ２ＳＯ４／ＨＺＳＭ５催化剂对甲烷脱氢芳构化（ＤＨＡＭ）反应的催化活性比不经酸化的（ＮＨ４）２ＷＯ４溶液（ｐＨ＝８～９）制备的Ｗ／ＨＺＳＭ５催化剂高得多．氧化前驱态催化剂的Ｈ２ＴＰＲ研究表明，ＷＨ２ＳＯ４／ＨＺＳＭ５试样的还原所需温度比Ｗ／ＨＺＳＭ５低得多；前者可还原至较低价态的Ｗ物种在负载总Ｗ量中所占比例也比后者高得多．Ｈ２ＴＰＲ及相关体系的ＥＰＲ和Ｒａｍａｎ表征结果相互佐证表明，用Ｈ２ＳＯ４酸化导致负载钨酸铵前驱溶液中一些由共边正八面体配位结构单元（ＷＯ６）ｎ－构成的聚钨酸根物种的生成；ＷＨ２ＳＯ４／ＨＺＳＭ５催化剂对ＤＨＡＭ反应催化活性之所以高，主要由于所负载的Ｗ前驱物种较大部分是（ＷＯ６）ｎ－基的Ｗ物种，而非（ＷＯ４）２－基Ｗ物种；在较低温度下就可被还原，且在ＤＨＡＭ反应条件下有一部分可还原至较低价态Ｗ４＋的（ＷＯ６）ｎ－物种很可能是催化活性位的前驱组成部分．更多还原

【Abstract】 It has been found experimentally that the acidification of the solution of (NH 4) 2WO 4 used for impregnation by H 2SO 4 enhances markedly the activity of the W/HZSM 5 based catalysts for non oxidative dehydro aromatization of methane (DHAM). The H 2 TPR results indicated that the temperature required for the H 2 reduction of the catalyst precursor of the W H 2SO 4/HZSM 5 derived from acidified solution of (NH 4) 2WO 4 (with pH=2～3) was much lower than that of the W/HZSM 5 derived from non acidified solution of (NH 4) 2WO 4 (with pH=8～9). It was estimated that, in the temperature region of 298～1200 K, the proportions of the W species reducible to W 5+ and W 4+ in the total amount of loaded W for the former were ～3 2 and ～10 times as high as that for the latter, respectively. This along with the results of the EPR and Raman investigations of the related systems would be in favor of the following viewpoint, i e, that the acidification by H 2SO 4 resulted in the formation of polytungstates species being built of octahedral group (WO 6) n - sharing edges, via the reaction such as 6(WO 4) 2- +7H +=(HW 6O 21 ) 5- +3H 2O, in the precursor solution, and that (WO 6) n - derived W species were more easily reduced by H 2 than those derived from (WO 4) 2- , and that the high DHAM activity was closely correlated with the polytungstate group (WO 6) n - as precursor of catalytically active species.更多还原