Nb2O5在t-ZrO2表面的分散状态与Br(φ)nsted酸特征

摘要

Nb2O5/t-ZrO2 catalysts with different loadings were prepared by aqueous solution impregnation using niobium oxalate as a precursor on tetragonal ZrO2 (t-ZrO2). The dispersion states with respect to niobia species on t-ZrO2 were characterized by powder X-ray diffraction (XRD), laser Raman spectroscopy (LRS), and UV visible diffuse reflectance spectroscopy (UV-Vis DRS). The catalytic activity was evaluated by the condensation reaction of iso-butene (IB) and iso-butyraldehyde (IBA) to 2,5-dimethyl-2,4-hexadiene (DMHD) and the Br0nsted acidity was evaluated by the Fourier-transform infrared spectroscopy of pyridine adsorption (Py-IR). The results reveal that the dispersion capacity rNb of Nb2O5 on t-ZrO2, which was determined by XRD quantitative phase analysis, is almost identical to the value predicted by the "incorporated model". The results also show that the Br0nsted acid sites are strongly related to the states of Nb2O5 onNb2O5/t-ZrO2.%以草酸铌为前驱物,四方相氧化锆(t-ZrO2)为载体,通过浸渍法制备不同负载量的Nb2O5/t-ZrO2催化剂.采用粉末X射线衍射(XRD)、激光拉曼光谱(LRS)、紫外-可见漫反射光谱(UV-Vis DRS)等技术对t-ZrO2表面Nb2O5分散状态进行表征;采用异丁烯(IB)与异丁醛(IBA)缩合生成2,5-二甲基-2,4-己二烯(DMHD)反应评价不同负载量的Nb2O5/t-ZrO2的催化性能,采用吡啶吸附红外(Py-IR)光谱表征催化剂Br(φ)nsted酸中心特征.结果表明,由XRD定量相分析方法测定的Nb2O5在t-ZrO2表面单层分散容量与“嵌入模型”预测值接近.Nb2O5/t-ZrO2表面Br(φ)nsted酸中心特征与Nb2O5聚集状态密切相关.