Selective Oxidation Of Isobutane Over The Catalysts Prepared With Keggin-type Heteropoly Acid

Methacrylic acid is one of the main raw materials for preparation of methylmethacrylate and its derivatives. At present, the technologies of the production ofmethyl methacrylate include acetone-cyanohydrin route, ethylene route and theselective oxidation of isobutane route. More and more people pay attention toisobutane oxidation due to its many advantages. However, the yield of methacrylicacid （MAA） is relatively low by this method, and there is still some distance fromindustrial production.Currently, the catalysts which are heteropoly compounds and mixed metal oxidecatalysts have been studied. Heteropoly compounds have good crystal structure,strong redox capacity and high catalytic activity in the selective oxidation of lightalkanes. In the past decades, heteropoly compounds are of great interest andimportance in this reaction. However, heteropoly compounds catalysts have acommon shortcoming, which are less stable in the reaction resulting in reducing theselectivity and yield of the products. At the same time, the research of metal oxidecatalysts also gets rapid development. Especially the series of Mo-V catalysts havebeen widely used in the selective oxidation of isobutane. In our early work, we havedone a lot of work in this field. The catalytic properties of the series of MoVTeO,MoVTePO, MoVTeSbO, MoVTePSbO and MoVTeCeO et al. mixed metal oxidecatalysts in the selective oxidation of isobutane have been studied. From heteropolycompounds and metal oxides point of view, the research work is as follows: First, the Te element replacing all the protons of HyPMo_12-xV_xO₄₀heteropolyacid catalysts in the Keggin structure for the selective oxidation of isobutane wasstudied. Combining with XRD, FT-IR, TG-DSC and SEM characterizations, theanalysis results showed that the structure of Te1.5+0.5xPMo12-xVxOn（x=0³ï¼‰catalysts has not been destroyed and still maintain Keggin structure. The experimentalresults showed that the introduction of the appropriate amount of Te element mayeliminate α-H from the olefins, Thereby increasing the selectivity of MAL.Second, we have prepared the Keggin structure HyPMo_12-xV_xO₄₀heteropoly acidas a raw material, trying to use a small amount of Te and Cs elements partialreplacement of protons in the heteropoly acid to prepareCs_2.0Te_0.2H_0.6+xPMo_12-xV_xO_n（x=0³ï¼‰ catalysts,and have examined the catalyticactivity in selective oxidation of isobutane reaction. The results showed that Cselement might enhance the stability of the catalysts. With the increasement of reactiontemperature, the conversion rate of isobutane is increased, and MAA which is theyield of the main product is correspondingly increased. When the temperature is toohigh, it may affect the thermal stability of the catalysts. After the introduction of Teelement, the selectivity to MAL and MAA has been markedly improved.Finally, we use a new method for preparing the Mo-V-Te-P-O metal oxidecatalysts, and the surfaces of catalysts were studied by means of XRD, FT-IR, XPS,and BET characterization. Meanwhile, they have better catalytic activity in selectiveoxidation of isobutane. When an appropriate amount of V was introduced, synergy ofeach component in the catalyst is strengthened. When V replaces the molybdenumatom of phosphomolybdic system, the conversion of isobutane and yield of MAAhave been significantly changed. It may be due to V5+in the surface activatingalkanes; Te4+eliminating the α-H from the olefins；（Mo6+）2responsible for Oinserted into the reaction intermediates.