TPD STUDY OF LABILE OXYGEN ON A (VO)(2)P2O7 CATALYST ACTIVE IN N-BUTANE PARTIAL OXIDATION

The interaction of oxygen with the surface of vanadyl pyrophosphate ha s been studied by Temperature-Programmed Desorption (TPD) under vacuum between 300 and 1000 K. It is shown that the adsorption of oxygen ont o the catalyst does not occur at temperatures in the range 300-570 K a nd that it is activated. The behaviour of the main TPD peak around 850 K agrees with second order desorption kinetics showing that adsorptio n is dissociative. The use of Intermittent TPD (ITPD), which is a part icular threshold method, shows that the labile superficial oxygen deso rbing up to 900 K is virtually homogeneous with an activation energy o f desorption of 327 KJ/mol O-2. Adsorption sites are tentatively assig ned to cus V4+, acting as Lewis acid centers, located in the (100) pla ne of the (VO)(2)P2O7 structure, in the prolongation of the vanadyl co lumns. The role of labile oxygen in the catalytic oxidation of butane into maleic anhydride is discussed. (C) 1998 Elsevier Science B.V.