掺杂元素对TiO_2/SO_4^(2-)固体酸特性的影响

Properties of solid acid TiO_2/SO_4^(2-) doping different oxides

为了进行掺杂元素对超强酸特性的影响研究,采用均匀沉淀法合成了Fe、Si、Al和Zr氧化物掺杂的TiO_2/SO_4^(2-)的固体酸(TiO2-MxOy),采用XRD、FTIR、NH3-TPD以及H2-TPR等分析方法对催化剂进行表征。以大豆油和甲醇的酯交换反应为活性评价反应,比较了各催化剂的催化活性。研究发现,除了Al外掺杂元素抑制了二氧化钛硫酸化浸渍处理形成硫酸氧钛的过程,其中Si的抑制作用最强。掺杂Fe、Si氧化物使样品中H2还原温度降低,其中以Fe掺杂的样品氢还原温度降低最为明显。NH3-TPD表征表明,Si、Zr和Fe等氧化物掺杂对超强酸表面酸性具有加强作用,而Al掺杂样品表面酸性与未经第二组分修饰的TiO_2/SO_4^(2-)相比有所降低。相比未掺杂第二元素的催化剂,各掺杂元素的添加使得催化剂活性都有不同程度的提高。将酯交换活性最好的掺Fe催化剂和TiO_2/SO_4^(2-)催化剂的重复使用情况进行了研究。结果发现,Fe_2O_3-TiO_2/SO_4^(2-)与TiO_2/SO_4^(2-)相比,经3次酯交换反应后活性降低不大。该研究可为后续固体酸的制备和应用提供理论基础。

Mixed oxides TiO2-MxOy（M=Fe,Si,Al,Zr）prepared by co-precipitation method were impregnated in aqueous solutions of sulfuric acid to form doped solid acid samples.These catalysts were characterized by XRD,FTIR,NH3-TPD and H2-TPR.Their catalytic activity was tested in the transesterification reaction between soybean and methanol.The results showed that the addition of second oxide into TiO2/SO2-4 could improve the catalytic activity and inhibit the formation of TiOSO4 in impregnation process except Al.The restraint effect was the strongest for silica.The doping of Si,Zr and Fe oxides could enhance surface acidity of catalysts while the addition of Al even made the acidity lower.The decrease of reduction temperature by H2 was larger for Fe-involving sample than for Si-involving one.The Fe doped catalyst was found to be readily reusable in activity upon reuse for three times with subtle decrease conversion.