In-situ control of vanadyl pyrophosphate deactivation by addition of sulfur dioxide during C4-C5 alkane oxidation

The nature and formation of strongly adsorbed species on the surface of vanadyl pyrophosphate during catalytic tests in n-butane and n-pentane oxidn. in maleic anhydride prepn., their role in the deactivation of surface reactivity, and the effect of SO2 in the control of this effect were studied by flow reactor tests, Fourier-transform IR studies in a flow reactor cell, and transient expts. using a TAP (Temporal Anal. of Products) reactor. A large fraction of the catalyst surface was blocked by strongly adsorbed intermediates/products that inhibited the surface reactivity considerably as compared to that of a clean surface. The presence of such species not only limited the no. of surface-available actives sites, but also changed their specific activity due to an inhibition of the available oxygen sites. The amts. of these species was limited and controlled by the addn. of small amts. of SO2 to the gas phase. It was suggested that the main role of SO2 is that of increasing the rate of desorption of these strongly adsorbed species, probably by competitive adsorption. [on SciFinder(R)]