Abstract: 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.

Key words: NiPMo₁₂ catalyst, Carbon dioxide, Propylene, Methacrylic acid, Keggin structure