MODIFICATION OF THE SURFACE PATHWAYS IN ALKANE OXIDATION BY SELECTIVE DOPING OF BRONSTED ACID SITES OF VANADYL PYROPHOSPHATE

The modification of Brønsted POH groups of (VO)2P2O7 by selective doping with K in an anhydrous medium causes a considerable modification of the surface oxidation pathways in C4- and C5-alkane oxidative transformation, with (i) a considerable decrease in the selective formation of maleic anhydride from n-butane and of maleic and phthalic anhydrides from n-pentane, (ii) an increase in the relative formation of phthalic anhydride with respect to maleic anhydride from n-pentane, and (iii) an increase in the formation of C-containing surface residues. It is suggested that these effects are due to an inhibition of the catalyzed transformation of furan-like intermediates to corresponding lactones and then to anhydrides in the presence of gaseous O2 and to a change in the relative rates of O-insertion and H-abstraction on these surface intermediates. The role of the dynamics of competitive surface transformations of adsorbed intermediates on the overall behavior of vanadyl pyrophosphate in C4- and C5-alkane selective oxidation is also discussed. © 1990 American Chemical Society.