Study On Catalyst For Selective Oxidation Of Isobutane To Methacrylic Acid

Methacrylic acid（MAA）is an important organic chemical raw material for the production of methyl methacrylate（MMA）.At present,the industrialized acetone cyanidation process suffers from many disadvantages such as the use of highly toxic HCN and the generation of a large amount of co-product ammonium bisulfate.The selective oxidation of isobutane to methacrylic acid（MAA）has attracted more and more attention because of its cheap raw materials and green routes.The heteropoly compound with Keggin structure are the most promising due to their adjustable redox ability and surface acidity,and achieve the excellent catalytic performance for oxidation of alkanes.In this thesis,the effect of the supports with different structure and the substituted metal ions with different content on the catalytic performance of the Keggin-type heteropolyacid compound catalyst for the selective oxidation of isobutane to MAA is investigated in detail.The specific research contents are as follows:Due to the lower specific surface area of heteropoly compounds（HPCs）,it is necessary to load the active HPCs on the supports with higher surface areas,which can obtain better dispersion and catalytic performance.Here,two different types of supports,supports-I(Cs₃PMo₁₂O₄₀,Cs_2.5H_0.5PMo₁₂O₄₀,Cs₄PMo₁₁VO₄₀and Cs₃HPMo₁₁VO₄₀)and supports-II（Ce O₂,WO₃/Zr O₂and silicalite-1 molecular sieve）,were chosen to support active（NH₄）₃HPMo₁₁VO₄₀（APMV）,It was found that the better results were obtained by impregnating 40 wt%active APMV phase onto the supports-I phase with similar Keggin structure,and it is believed that the formation of coherent interfaces between two structural well-matched phases with the similar Keggin anions greatly promotes interfacial transfer abilities of electrons and lattice oxygen,which is responsible for the efficient oxygen insertion to maximize MAA selectivity and conversion of isobutane.In addition,we also investigated the effects of doping metal ions with different proportions on the structure and catalytic performance of the HPCs catalysts.The study found that compared with the undoped（NH₄）_1.85H_2.15PMo₁₁VO₄₀catalyst,the specific surface area,amount of acid sites,and immigrating amount of V atom in Keggin unit into the secondary structure were strongly dependent on the substituted metal ions and their content.The optimum activity was obtained over（NH₄）_1.85Cs_0.5H_1.65PMo₁₁VO₄₀catalyst,which could provide a larger surface area of 37.72 m~2/g,a higher amount of acid sites（82.47μmol/g）,and more VO²⁺species and V₂O₅clusters from the immigration of V atom in Keggin structure.In addition,because the replacement catalyst of Cu ions accelerates the electron transfer efficiency and accelerates the catalytic cycle of isobutane oxidation,the desorption speed of MAA is accelerated,and the catalyst exhibits excellent selectivity to MAA.