二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应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.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.

Study on NiPMo/TiO2 Catalyst for Direct Synthesis MAA from Propylene and Carbon Dioxide

The NiPMo/TiO2catalystswere prepared fromhydrolysis tetrabutyl titanate by aqueous solutions ofNi salts of the 12-molybdophosphoric acid via the sol-gel method. Chemical composition, thermal stability, chemisorption character and reaction behaviours have been studied byvarious techniques, such as, 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 polyoxomolybdate was introduced to the surface of titanium dioxide and formed the NiPMo/TiO2hybrid materials. Therefore, a coordination structure of the NiPMo/Ti catalysts was proposed. At the temperature of 623 K, the catalyst still remained the original Keggin structure of polyoxomolybdate. The chemisorbed IR showed that CO2chemisorbs at bridging oxygen of Ni-O-Mo(Lewis base site) and Ni2+(Lewis acid site) forming bridged absorption states Ni(Ⅱ)←O-(CO)←(O--Ni), and propylene chemisorbs on the surface of catalystwith three absorption states. Underthe reaction conditions of 563 Kand 1MPa, the main reaction products of CO2and propylene on the surface of catalysts were MAA, the conversion of propylene was 3.2%, and the selectivity ofMAAwas 95%