Oxidation of Isobutane Catalyzed by Partially Salified Cesium Molybdovanadophosphoric Acids

Abstract

The catalytic activity for the oxidation of isobutane catalyzed by 12-molybdophosphoric acid was much changed by the V5+- and Cs+-substitution for Mo6+ and H+, respectively. The best yield of methacrylic acid was 9.0% and was obtained for the heteropoly catalyst with V and Cs contents of 1 and 2.5, respectively. The high catalytic activity obtained for Cs2.5Ni0.08H1.34PVMo11O40 is presumably due to the high surface area. The activities of 12-molybdovanadophosphoric acids as well as those of 12-molybdophosphoric acid partially salified with Cs+ were controlled by the oxidizing ability of catalysts. The conversion vs selectivity relationships, the simulation of the data, and kinetic results for Cs2.5Ni0.08H1.34PVMo11O40 and Cs2.5Ni0.08H0.34PMo12O40 catalysts show that the first steps, i.e., selective and complete oxidation reactions of isobutane, are rate-determining and mainly catalyzed by molybdenum ion and that vanadium ion efficiently accelerates the selective oxidation of methacrolein to methacrylic acid. Cs+-substitution for H+ in H3.84Ni0.08PVMo11O40 greatly change the selectivity up to a Cs content of 2.5 and suppressed the elimination of the vanadium ion from the Keggin anion.

Comprehensive Study of Isobutane Selective Oxidation Over Group I and II Phosphomolybdates: Structural and Kinetic Factors

“…The methacrylic acid formation displayed by the BaH[PMo 12 O 40 ] compound matches one Previous studies have proposed that isobutene acts as an intermediate for methacrolein and methacrylic acid production [46,50,[67][68][69], although other authors dispute this claim [70][71][72]. Similarly, some studies indicate that methacrolein is an intermediate in the formation of methacrylic acid [45,49,69], while others give evidence negating this finding [70,72,73]. Previous work has indeed shown methacrolein and methacrylic acid production from respective isobutene and methacrolein oxidations over heteropoly compounds [20,71,[74][75][76][77].…”

“…Methacrylic acid has been shown to form from the oxidation of isobutane over heteropoly compounds such as phosphomolybdates [7,[44][45][46][47][48][49][50]. Typically, methacrylic acid is not formed for isobutane selective oxidation with the low-pressure TPRS system employed in this study [22][23][24].…”

Mechanistic Investigation into the Rearrangement of Lactone into Methacrylic Acid over Phosphomolybdic Acid Catalyst

“…The lactone has not been reported by other research groups. Methacrylic acid was an expected product and is commonly reported from catalytic oxidations conducted using higher pressures and non-molecular flow conditions [2,3,5,9,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], but was not observed. The lactone is an isomer of methacrylic acid and its appearance, and the concomitant absence of methacrylic acid, suggests that it is an intermediate for methacrylic acid.…”

Selective Oxidation and Oxidative Dehydrogenation of Isobutane over Hydrothermally Synthesized Mo–V–O Mixed Oxide Catalysts

“…In the past decades, studies have focused mainly on one-step oxidation of isobutane to partial oxidation products via Keggin-type heteropolyoxometallate compounds [1][2][3][4][5] or mixed oxide catalysts [6][7][8][9][10]. Methacrolein (MAL) and methacrylic acid (MAA) are the key intermediates in one of the existing processes for the production of methyl methacrylate.…”