alpha(II)-(V1-xWx) OPO4 catalysts for the selective oxidation of n-butane to maleic anhydride

摘要

The vanadyl pyrophosphate (VPP) based catalyst is unique in converting n-butane selectively (60-70%) into maleic anhydride (MAN), whereas a MAN selectivity of 20% may be regarded as high for structurally different catalyst systems. We present novel vanadium phosphorus oxides and mixed metal phosphate solid solutions tested for n-butane oxidation to MAN with a selectivity of> 30%. The majority of the catalysts were prepared by solution combustion synthesis. (V1-xWx) OPO4 with a II structure was found to be more active and selective in the oxidation of n-butane compared to beta-VOPO4. By adjusting the tungsten content the oxidation state of vanadium in (V1-xWx) OPO4 can be tuned between 4.74 and 4.99, which is regarded as a key factor for MAN production. All catalysts were structurally stable, but the specific surface area increased during the reaction, as detected by X-ray diffraction and N-2 physisorption, respectively. (V1-xMox) OPO4 was also stable, but the MAN selectivity was lower compared to beta-VOPO4. Low conversions result from the low surface area of the screening samples, however, could be overcome by advanced synthesis protocols.