Oxidation of isobutane on a heteropolycompound hydrogen reservoir

The selective oxidation of isobutane to methacrylic acid (MAA) has been studied on Cs1.6H2.4P1.7Mo11V1.1O40 which is a heteropolycompound (HPC). The oxidation mechanism isobutane --> isobutene --> MAL --> MAA has already been proposed previously with a rate determining step corresponding to the first step of the reaction, i.e., to dehydrogenation of isobutane leading to isobutene. Here we show that the HPC which is active in the oxidation of isobutane possesses, in the reduced state, anionic vacancies able to store reactive hydrogen species H* presenting the ability to diffuse through the solid. Such a result is of great importance since dehydrogenation requires the abstraction of hydrogen from the molecule which could be performed by a lacunar phase. Therefore, a mechanism of the dehydrogenation step is proposed. involving a heterolytic abstraction of a H- species from the alkane.