An antimony(V) substituted Keggin heteropolyacid, H4PSbMo11O40: Why is its catalytic activity in oxidation reactions so different from that of H4PVMo11O40?

An antimony(V) containing α-Keggin type acidic polyoxometalate, H4PSbMo11O40, was prepared by reacting NaMoO4, H3PO4 and Sb2O3 in the presence of aqua regia to appraise its reactivity compared to the well known vanadate analog, H4PVMo11O40. Characterization was by X-ray diffraction, MALDI-TOF MS, IR, UV–vis and 31P NMR spectroscopy. Catalytic redox reactions, such as oxidative dehydrogenation using O2 and N2O as terminal oxidants were studied and showed very different reactivity of H4PSbMo11O40 versus H4PVMo11O40. It was found by DFT calculations that in contrast to analogous H4PVMo11O40 where vanadium centered catalysis is observed, in H4PSbMo11O40 catalysis is molybdenum and not antimony centered.

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► An antimony(V) substituted phosphomolybdic acid was prepared and characterized.
► Different reactivity was expected versus known analogous vanadium substituted compound.
► DFT calculations explain the difference in the catalytic activity.