ROLE OF THE PRODUCT IN THE TRANSFORMATION OF A CATALYST TO ITS ACTIVESTATE

OXIDE catalysts, which are used in a broad range of important industri al proccsses(1-4), are generally prepared in the form of a precursor w hich is converted into the active catalytic form only under well defin ed reaction conditions. A vanadium phosphorus oxide catalyst is used t o effect selective oxidation of n-butane to maleic anhydride: (VO)(2)P 2O7 is considered(5-7) to be the main active component, and is prepare d from the precursor VOHPO4.O.5H(2)O. Here we use in situ Raman spectr oscopy to study the conversion of this precursor to the active form in real time. We find that, during this process, the crystalline structu re of VOHPO4.O.5H(2)O becomes totally disordered at the same time as s electivity for maleic anhydride becomes apparent. Furthermore, our res ults indicate that this Product seems to play a role in bringing about this change; thus, it seems that the selective reaction product assis ts in the creation of the active sites. We suggest that this phenomeno n might be quite general in oxide catalysis.