PO_4^(3-)改性的二氧化钛固体酸催化剂

Phosphate-Promoted TiO_2 Solid Acid Catalysts

通过沉淀、老化、过滤、洗涤、干燥、浸渍和焙烧等过程,由TiCl4和H3PO4制备了PO43-改性的二氧化钛固体酸催化剂,用Hammett指示剂法、正丁胺滴定法和吡啶吸附FT-IR光谱法测定了催化剂酸性质,用XRD,FT-IR,TG-DTA和N2-吸附对其进行了表征,研究了PO43-的质量分数和焙烧温度对其酸性、结构和催化性能的影响。XRD和TG-DTA结果表明PO43-稳定TiO2的锐钛矿晶相和抑制晶粒长大。FT-IR分析表明PO43-物种与TiO2表面双桥螯合配位键合。N2-吸附和正丁胺滴定结果表明PO43-的质量分数小于7.5%时,表面积、孔容和总酸量随着PO43-的质量分数增加先增大后减小。Hammett指示剂法和吡啶吸附的FT-IR光谱结果表明,PO43-改性的二氧化钛固体酸催化剂在425~575℃焙烧可以形成固体超强酸,表面上同时存在L酸中心和B酸中心。PO43-改性的二氧化钛固体酸在乙酰乙酸乙酯和乙二醇的缩酮化反应中具有良好的催化性能。

The phosphate-promoted TiO2 solid acid catalyst was prepared from TiCl4, and H3PO4 by precipitation, aging, filtering, washing, drying, impregnation and calcination processes. The acidic property of catalyst was determined by Hammett indicator and n-butylamide-titration as well as pyridine-adsorption FT-IR spectrometer. The characterization of the catalyst was performed using XRD, FT-IR, TG-DTA, N2-adsorption methods. The effect of mass fraction of phosphate and calcination temperature on the acidic property, textural property and catalytic performance of phosphate-promoted TiO2 solid acid catalysts was studied. TG-DTA curves and XRD patterns show that phosphate stabilizes the anatase phase and prevents grains from growing. FT-IR spectra shows that phosphate species strongly bind with the TiO2 surface bidentately. N2 adsorption and n-butylamide-titration show that surface area and porous volume as well as total acidity increase with the increase of mass fraction of phosphate when it is less than 7.5% and thereafter decrease. Hammett indicator and pyridine-adsorption FT-IR spectra show that solid superacid is formed at 425-575°C and there are Lewis and Bronsted acidic centers on surface. The phosphate-promoted TiO2 solid acid catalyst has good catalytic performance in the ketalization of ethyl acetoacetate and 1, 2-ethandiol.