二氧化碳和丙烯直接合成甲基丙烯酸CuPW/TiO2催化剂的研究

用溶胶-凝胶法以磷钨酸(TPA)的铜盐溶液水解钛酸四丁酯制备了CuPW/TiO2催化剂。使用ICP、XRD、TG-DTA、IR、TPD-MS和微反技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能。实验结果表明杂多钨酸盐与TiO2表面通过O2-桥发生键合作用。在623 K下,杂多阴离子仍保持原有的Keggin结构。CO2在Lewis酸位Cu(Ⅱ)和Lewis碱位Cu—O—W的桥氧协同作用下形成卧式吸附态。丙烯以分子吸附态在催化剂上选择吸附。在563 K,1 MPa和空速1 500 h-1的反应条件下,丙烯的摩尔转化率为4.3%,产物MAA(甲基丙烯酸)的选择性为96%。

STUDY ON CuPW/TiO2 CATALYST FOR DIRECT SYNTHESIS OF MAA FROM PROPYLENE AND CARBON DIOXIDE

The CuPWTiO2 catalysts were prepared with tetrabutyl titanate hydrolysis by aqueous solutions of Cu salts of the 12-tungstophosphoric acid via sol-gel method. Chemical composition, thermal stability, chemisorption character and reaction behaviours have been studied by different techniques including X-ray diffraction, thermogravimetric analysis, infrared spectrum analysis, inductively coupled plasma atomic emission spectroscopy, temperature-programmed desorption, and microreactor. The experimental results showed that inorganic precursor polyoxotungstate was introduced on the surface of titanium dioxide and formed to the CuPW/TiO2 hybrid materials. Under temperature of 623 K, the catalyst still remains the original Keggin structure of TPA. The experimental results showed also that CO2 chemisorbs at bridging oxygen of Cu—O—W(Lewis base site) and Cu2+(Lewis acid site) to form bridged adsorption states, that propylene chemisorbs on the surface of catalyst to form molecular absorption states, and that the main reaction products of CO2 with propylene on the catalysts are MAA, with propylene conversion of 4.3% under the reaction temperature of 563 K and 1 MPa, MAA selectivity of 96%.