Preparation,Characterization And Catalytic Performances Of Polyoxometalates Catalysts For The Synthesis Of Methacrylic Acid From Carbon Dioxide And Propylene

Methacrylic acid is one of important material in organic synthesis. Carbon dioxide, one of greenhouse gas and a bulk industry emissions, can be reused as a renewable resource of carbon and oxygen for producing chemistry. Utilization of carbon dioxide and propylene as starting material for direct synthesis of methacrylic acid provides an attractive alternative to organic synthesis, environmental protect and utilization of carbon. The conversion was determined by activation of carbon dioxide and selective activation of propylene. In this thesis, the preparation, chemical component, molecular structure and chemisorption of polyoxometalates catalysts and titanium oxide-supported catalysts were investigated and systematically evaluation of catalytic performance was also provided in this paper.1. The polyoxometalates catalysts were prepared by the method surface reaction modification. The mono-mental heteropolyanion acid (12-molybdophosphoric acid, tungstophosphoric acid) and dimetal heteropolyanion acid (H3PMo6W6O40, H6Mo9V3O40) were modified by transtion mental ion Cu(Ⅱ) and Ni(Ⅱ). The titanium oxide supported heteropolyacid catalyst was prepared by sol-gel method. Chemical component, surface component, thermal stability, molecular structure, specific surface area and phase structure were investigated by BET, ICP, XPS, IR, Raman, XRD, TG-DTA, EXAFS and TPR. The chemisorption properties of carbon dioxide and propylene on these catalysts were studied by chemisorption infrared spectroscopy and the corresponding states of chemisorb were proposed. The desorption performance of carbon dioxide and propylene were investigated by temperature programmed desorption-mass spectrometry (TPD-MS) technique. The reaction performance of catalysts evaluated on a microreactor.2. The results of BET showed: Specific surface area of bulk catalysts were above 10-16m2.g-1 and titanium dioxide supported catalysts were 55 m2.g-1. ICP , IR and Raman results revealed the polyoxometalates maintained keggin structure. For the supported catalysts, the IR absorption became stranger with the increasing of loading. XPS and XRD were used to study supported catalysts, the heterpolycompounds were dispersed on the surface of titanium oxide with amorphous or microcrystalline structure and titanium oxide was anatase phase structure. TG-DTA revealed, calcining at 350℃,the catalysts still remain keggin structure. Above 350℃,decomposition started. This result was also confirmed by XRD , IR and Raman study . The thermal stability was in the order as follow: dimetal heteropolyanion acid > monumental heteropolyanion acid catalyst. Titanium oxide-supported catalysts > bulk catalysts. The EXAFS study DFT analysis revealed: transion mental ion Cu(Ⅱ) and Ni(Ⅱ) bonded with mental ion of heteropoly acid (M=Mo,W,V) and formed iso-nuclear bridging structure. In this connection , the complex structure model of supported catalysts was proposed. Titanium gel bonded with-terminal oxygen through dehydration under heat trement.3. The IR study of chemisorption of carbon dioxide and propylene on catalyst revealed: the active center was iso-nuclear bridging structure. Carbon dioxide absorbed on Lewis acid site A(Ⅱ) and Lewis base site(bridged oxygen). With bridging absorption. Otherwise, carbon dioxide could shearing absorb on titanium oxide that have benefit in with activity of carbon dioxide. Propylene could chemisorb on the kinds of catalysts(supported and bulk). As two states: clouble bond of C=C chemisorbed on catalyst forming d-π complex. Hydrogen atom in =C-H and CH3 chemisorbed on catalyst. The desorption properties of carbon dioxide and propylene were deteriminated by TPD-MS method. Only one desorption peak of bulk catalyst identified bringing absorption had been found. There were two desorption peak of supported catalyst. Identified bridging absorption and shearing absorption respectivity. The desorption property of propylene was more complicated than carbon dioxide, which were formed by many desorption peaks added together.4. The activity of catalys...