摘要
采用Hammett指示剂、吡啶吸附红外光谱(Py-IR)和微反测试等方法,考察了负载型Nb2O5催化剂表面酸性特征和对异丁烯(IB)/异丁醛(IBA)缩合生成2,5-二甲基-2,4-己二烯(DMHD)反应(称为Prins缩合)的催化活性。结果表明,催化活性与催化剂表面酸性特征有关。在Nb2O5/γ-Al2O3表面,只有当Nb2O5负载量超过一定量后才形成可检测的B酸位,并对IB/IBA缩合生成DMHD的反应才有明显的催化活性。随着Nb2O5负载量增加,Nb2O5/γ-Al2O3表面B酸位数增加且强度增强,催化剂的活性和产物的选择性增加;当Nb2O5负载量超过分散容量后,因表面形成较强的B酸位而导致DMHD选择性降低。将TiO2引入Nb2O5/γ-Al2O3,使催化剂表面B酸位数增加,从而提高了催化剂的活性;而将ZrO2引入Nb2O5/γ-Al2O3,则导致催化剂表面B酸位数大幅度减少,从而显著降低了催化剂的活性。催化剂表面B酸位是IB/IBA缩合生成DMHD的反应活性中心。
The catalytic activity and surface acidity of supported Nb2O5 catalysts were investigated by the means of Hammitt indicator method, pyridine adsorption Fourier-transform infrared （Py-IR） spectroscopy technology and activity test in a micro-reactor for the condensation reaction from iso-butene （IB） and iso-butyraldehyde （IBA） to 2,5-dimethyl-2,4- hexadiene （DMHD）（called Prins condensation）. The results showed that the catalytic activity of the supported Nb2O5 catalysts for the condensation reaction was related to the acidic feature on their surface. The Bronsted acid site （BAS） was only devolped when Nb2O5 loading was beyond the threshold value, and BAS and its strength increased with Nb2O5 loading on Nb5O5/γ-Al2O3 catalysts. The DMHD selectivity was decreased by BAS strengthing after the Nb2O5 loading beyond dispersion capacity. The catalytic activity was enhanced due to BAS increasing through surface modified γ-Al2O3 by TiO2, however it was declined due to BAS decreasing by ZrO2. It is suggested that the catalytic activity of supported Nb2O5 to DMHD from IB and IBA was obtained only in the presence of weakly and moderately acidic BAS.
出处
《石油学报（石油加工）》
EI
CAS
CSCD
北大核心
2006年第4期18-24,共7页
Acta Petrolei Sinica(Petroleum Processing Section)
基金
国家重点基础研究发展规划资助项目(G1999022400)
