【摘要】 <正> Keggin型杂多酸化合物的热稳定性高,又具有强酸性和氧化还原性,故其催化作用很引人注目.由于其结构上的特点,反应物分子能出入催化剂的体相内部,因而体相中的活性中心也起作用,被称作“假液相”催化.杂多酸用于甲醇催化转化为烃的反应有不少研究.据报道,12-钨磷酸(H₃PW₁₂O₄₀)和12-钨硅酸(H₄SiW₁₂O₄₀)、12-钨磷酸铜(Cu_3/2PW₁₂O₄₀)对甲醇转化反应都有相当高的活性.1,4-二嗪和1,3,5-三嗪的12-更多还原

【Abstract】 The conversion of methanol to hydrocarbons over H3PW12O40 and its salts was investigated. It was found that the activity of H3PW12O40 gradually decreased as the reaction proceeded, while using Ag3PW12O40 as catalyst, the reaction showed an induction period, then the activity of this catalyst increased with the reaction time and reached a steady value after 3 hours. Only a few weakly acidic sites were observed on Ag3PW12O40 by n-butylamine titration; nevertheless, new acid sites appeared during the induction period as shown by pyridine poisoning.The activities of Ag(Ⅰ), Cu(Ⅱ) and Fe(Ⅲ) salts of H3PW12O40 were slightly higher than that of H3PW12O40,while Mg, Ca, Sr, Ni, Co, and La salts showed lower activity. The higher activity of Ag(Ⅰ), Cu(Ⅱ) and Fe(Ⅲ) salts was probably caused by their reducibility.It was reported in the literature that Cs3PW12O40 had higher activity, but in our experiments Cs salt showed very low activity. It was found that as the x in CsxH3-xPWl2O40 changed from 0 to 1, 2 and 3, the surface area of the catalyst markedly increased, and the activity showed a maximum at x=2.5 and dropped rapidly to nearly zero at x=3. These phenomena might be explained by the difference in turnover frequency of the acid sites on the surface and of those in the bulk.更多还原