【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。更多还原

【Abstract】 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 Brnsted acid site （BAS） was only devolped when Nb₂O₅ loading was beyond the threshold value, and BAS and its strength increased with Nb₂O₅ loading on Nb₂O₅/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.更多还原