二氧化碳和丙烯直接合成甲基丙烯酸NiPMo12催化剂的研究

用硝酸镍对磷钼酸(MPA)进行改性制得NiPMo12催化剂.采用ICP,XRD,Tg-DTA,EXAFS,IR,TPD-MS和微反技术研究了催化剂的化学组成、分子结构、化学吸附性质和催化反应性能.350℃下NiPMo12催化剂仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni—O—Mo的桥氧协同作用下可生成CO2桥式吸附态Ni(Ⅱ)←O—(CO)—(O-—Ni).丙烯在催化剂上存在多种吸附态.在氢转移和碳插入作用下得到了反应产物MAA.在290℃和1MPa的反应条件下,丙烯的摩尔转化率为2.6%,产物MAA选择性为96%.

Studies on NiPMo12 Catalyst for Direct Synthesis MAA from Propylene and Carbon Dioxide

NiPMo12 catalyst was prepared by using the reaction of MPA and nickel nitrate. The chemical composition, molecular structure, chemisorption character and reaction behaviour were studied by different techniques including inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, thermogravimetric analysis, infrared spectrum analysis, extend X-ray absorption fine structure, temperature programmed desorption and microreactor, respectively. At 350 ℃, the catalyst still remained the original Keggin structure of MPA. The experimental results show that CO2 chemisorbs at bridging oxygen of Ni—O—Mo (Lewis base site) and Ni2+ (Lewis acid site) to form bridged adsorption Ni(Ⅱ)←O—(CO)—(O-—Ni) , and propylene chemisorbs on the surface of catalyst to form three adsorption states, and the main reaction products of CO2 with propylene on the catalysts are MAA and β-butenic acid, with propylene conversion of 2.6%, MAA selectivity of 96%, at the reaction temperature of 290 ℃ and 1 MPa. MAA and β-butenic acid were synthesized by the route of hydrogen transfer and carbon-insert.