硅钨酸为前驱物的W(Si)/HZSM-5-基催化剂上甲烷脱氢芳构化

Dehydro-aromatization of CH_4 over W(Si)/HZSM-5-based Catalysts Prepared with Silicotungstic Acid as the Impregnant

报道以硅钨酸H_8(Si(W_2O_7)_6)代替钨酸铵作为W组分的前驱物,制备一类HZMS-5负载W-基催化剂。在1073K、0.1MPa、原料气组成为CH_4+10％Ar、相应之GHSV=960h^(-1)的反应条件下,考察其对甲烷无氧条件下脱氢芳构化(DHAM)的催化活性。结果表明,W负载量以6％～9％(质量百分数)为佳;在6％W(Si)/HZSM-5催化剂上,甲烷转化率最高可达～20％,相应苯选择性为～60％。焙烧温度对催化剂表面W物种的存在形态及至对其DHAM催化活性有相当影响;以～773K焙烧制得催化剂的活性为佳。引入适量助剂Ni促使氧化前驱态催化剂的还原温度有所下降,并延长催化剂的寿命。

Using silicotungstic acid in place of ammonium tungstate as the impregnant in preparation of the catalyst precursor, a series of W(Si)/HZSM-5-based catalysts were prepared. The results of catalyst evaluation for DHAM reaction showed that, under reaction conditions of 1 073 K, 0. 1 MPa, feed-gas composition at CH4 + 10%Ar and GHSV= 960 h-1 and over a 6%W(Si)/HZSM-5-based catalyst after 20 min of induction period of reaction, methane conversion can reach -20% with selectivity to benzene at -60%. It is found experimentally that calcination temperature has pronounced influence on the existing forms of catalytically active W-containing species, in turn on the catalyst activity. High calcination temperature (>773 K ) would be apt to lead to formation of WO3 crystallites, as demonstrated by the results of Raman and XRD investigations, and thus, selecting - 773 K as calcination temperature would be appropriate. Incorporation of an appropriate amount of Ni into W(Si)/HZSM-5 was found to obviously improve the coking-resistant performance of the catalyst, thus, prolonging lifetime of the catalysts.