Improvement of the catalytic performance of supported (NH4)3HPMo11VO40 catalysts in isobutane selective oxidation

High surface area polyoxometalate catalysts were prepared by supporting the same amount of (NH4)3HPMo11VO40 (APMV) active phase on various silica carriers (commercial SiO2, SBA-15, ZrO2-grafted SBA-15), and on Cs3PMo12O40 (CPM). The catalytic performance of the samples was evaluated in the selective oxidation of isobutane to methacrolein and methacrylic acid at 340 °C. The highest yield (8 mol.% of methacrolein and methacrylic acid) was obtained with CPM-supported APMV at 15.3% isobutane conversion. To investigate the effect of the support on the structure and catalytic properties of the active phase, the structural and textural properties of the catalysts were examined by nitrogen physisorption, FT-IR and Raman spectroscopies, and their reactivity by TGA, temperature-programmed H2-XRD and NH3-TPD. The support was found to exert a strong effect on the dispersion, the thermal stability and the acidity of APMV. The stability of silica-supported catalysts was lower than when CPM support was used, which was ascribed to the low APMV coverage (less than one theoretical monolayer). The decomposition of bulk APMV was delayed by supporting it on CPM, and this support favored the strongest acid sites, which are necessary to activate alkanes to acids.