A novel versatile platform as efficient deoxydehydration (DODH) catalysts: Keggin polyoxometalates

Despite their high tunability and versatility, the use of Keggin polyoxometalates (POMs) as deoxydehydration (DODH) catalysts has never been investigated. In this contribution, we report for the very first time the promising catalytic performances in DODH of 1,2-hexanediol (chosen as model substrate) of tetrabutylammonium phosphododecamolybdate (TBAPMo12) (100% conversion, 52% selectivity). This Keggin POM was easily obtained by ion metathesis and precipitation of the commercially available H3PMo12O40 (HPMo) with TBABr. Additionally, we show that it is possible to greatly improve the catalytic performances of (TBA)3PW12O40 (TBAPW12), which in its pristine form is not as performant (45% conversion, 23% selectivity) as its Mo counterpart. To do so, the monolacunary form of PW was synthesized ((TBA)4H3PW11O39 = TBAHPW11) and then metalated with a Re precursor, yielding a very active (100% conversion, 73% selectivity) (TBA)4PW11ReVO40 (TBAPW11Re) mixed-metal compound. TBAPW11Re was fully characterized by IR, 31P NMR, ICP-AES, UV-vis and elemental analysis and its catalytic nature was investigated together with TBAPMo. Cold filtration tests and recycling experiments revealed that it is their dissolution that leads to DODH-active species.