Abstract
The interaction of oxygen with the surface of vanadyl pyrophosphate has been studied by Temperature-Programmed Desorption (TPD) under vacuum between 300 and 1000 K. It is shown that the adsorption of oxygen onto the catalyst does not occur at temperatures in the range 300–570 K and that it is activated. The behaviour of the main TPD peak around 850 K agrees with second order desorption kinetics showing that adsorption is dissociative. The use of Intermittent TPD (ITPD), which is a particular threshold method, shows that the labile superficial oxygen desorbing up to 900 K is virtually homogeneous with an activation energy of desorption of 327 kJ/mol O 2. Adsorption sites are tentatively assigned to cus V 4+, acting as Lewis acid centers, located in the (100) plane of the (VO) 2P 2O 7 structure, in the prolongation of the vanadyl columns. The role of labile oxygen in the catalytic oxidation of butane into maleic anhydride is discussed.
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