Atypical synergetic effect between Te- and V-substituted phosphomolybdic cesium salt and LAMOX-type phases for the oxidation of isobutane into methacrylic acid

Mechanical-phase mixtures of a phosphomolybdic cesium salt containing V and Te as counter-cations and α-La2Mo2O9 (LM) or β-La2Mo1.9V0.1O8.95 (LMV) have been studied as catalysts for the partial oxidation of isobutane into methacrylic acid (MAA) and methacrolein (MA). The catalysts with 50 wt.% of LMV in the phase mixture appeared very efficient at 360 °C and atmospheric pressure with selectivity and yield into MAA and MA, respectively, equal to 59% and 12.4%. The characterization of the catalysts allowed to propose that the synergetic effect taking place between the phases results primarily from a support effect of the lanthanum molybdate stabilizing the phosphomolybdic salt and preventing its sintering. The origin of such effect has been related to crystallographic fits between the two phases. This type of structure- related synergetic effect had never been reported in catalytic oxidation reaction for which most of the time, the spreading of one phase on the other is taking place.