碱性助剂对负载型固体酸催化剂上异丁烯齐聚的影响

采用浸渍法制备了Al2(SO4)3/SiO2催化剂,用热重-微商热重分析、X射线衍射、氨程序升温脱附和吡啶吸附傅里叶变换红外光谱等表征手段,研究了催化剂表面活性组分的存在状态,以及添加碱性助剂NaOH对催化剂酸性质的影响。表征结果显示,添加NaOH后,不改变Al2(SO4)3在载体表面的高度分散状态;Al2(SO4)3/SiO2催化剂表面基本为B酸中心,添加NaOH后,部分中强酸中心转化为弱酸中心;在40℃的低温条件下,中强酸中心是催化异丁烯齐聚反应的活性中心。稳定性实验结果表明,添加适量的NaOH后,Al2(SO4)3/SiO2催化剂具有高且稳定的二异丁烯(DIB)选择性,二聚体中DIB的选择性在反应时间70h内始终高达95%。

Effect of Alkaline Additive on Isobutene Oligomerization over Supported Solid Acid Catalyst

Supported Al2(SO4)3/SiO2 catalyst was prepared by impregnation.The existing state of Al2(SO4)3 and the effect of NaOH addition on acidity of Al2(SO4)3/SiO2 catalyst were studied by means of TG-DTG,XRD,NH3-TPD and Py-FTIR.Al2(SO4)3 was highly dispersed on surface of support and remained without obvious change after addition of NaOH.Brnsted acid sites dominated the solid surface.Addition of NaOH led to partial conversion of medium-strong acid sites to weak ones.The high activity of the catalyst attributed to the medium-strong Brnsted acid sites of the catalyst when isobutene oligomerization was carried out at 40 ℃.The stability test showed that Al2(SO4)3/SiO2 catalyst modified with suitable amount of NaOH exhibited high and stable diisobutene selectivity.The selectivity to diisobutene in dimers maintained as high as 95% during the on-stream period of 70 h.