H_2SO_4处理的Nb_2O_5/γ-Al_2O_3催化剂表面酸性与催化性能研究

The Surface Acidity and Catalytic Performance of Nb_2O_5/γ-Al_2O_3Catalysts Treated by Sulphuric Acid

用Hammett指示剂法、红外光谱(IR)、示差扫描量热鄄热重法(DSC鄄TG)和微型催化反应装置等研究了H2SO4处理的负载型Nb2O5/γ鄄Al2O3催化剂表面酸性和催化异丁烯(IB)与异丁醛(IBA)反应生成2,5鄄二甲基鄄2,4鄄己二烯(DMHD)的催化性能。结果表明随所用H2SO4浓度增加,Nb2O5/γ鄄Al2O3催化剂表面酸性增强,B酸量增加,L酸量先增加后下降。经H2SO4处理的Nb2O5/γ鄄Al2O3催化剂的催化活性明显增加,但当H2SO4浓度超过0.05mol·L-1时催化活性又急剧下降,这可能是因为在H2SO4处理的催化剂表面形成的强酸中心上,产物分子进一步转化为积炭且封闭催化剂活性表面,导致催化活性下降。

The surface acidity and catalytic performance of γ-alumina-supported niobia catalysts treated by H2SO4 with different concentration have been studied by means of Hammett indicator method, infrared (IR) spectroscopy, differential scanning calorimetry (DSC)-thermogravimetry (TG), and the condensation reaction of isobutene (IB) and isobutylaldehyde (IBA) to 2,5-dimethyl-2,4-hexadiene (DMHD). The results have revealed that treatment of Nb2O5/γ-Al2O3 catalysts with H2SO4 is effective to enhance the surface acid strength and increase the amount of Br?觟nsted acid sites on the Nb2O5/γ-Al2O3 catalysts. The catalytic activity increases with the amount of acid sites on the catalysts, however, the formation of acid sites with higher strength results in deactivation of the catalysts due to coking.