Study by XPS and TPD of the interaction of n-pentane and n-butane with the surface of non-equilibrated' and equilibrated' V–P–O catalysts (original) (raw)

Surface characterization of V±P±O catalysts used in the oxidation of n-butane and n-pentane to maleic and phthalic anhydrides is reported. Two different states for the same catalyst are selected: after a short time under reaction conditions (100 h), the`non-equilibrated' system, and after a much longer time-on-stream (1000 h), the`equilibrated' catalyst. Characterization has been carried out by following the desorption of molecules with a mass spectrometer after catalysts had been in contact with the hydrocarbons and/or O 2 mixtures at 613 K. Valence state of vanadium under environmental conditions similar to those used in the desorption studies was obtained by XPS. It was concluded that both V V and V IV are capable of interacting with the hydrocarbon and that not all the V IV present at the (VO) 2 P 2 O 7 surface can interact. On the other hand, desorption of molecules resulting from such interaction occurs at lower temperatures from V IV -rich surfaces (`equilibrated' catalyst), than from the V V richer surface (`non-equilibrated' catalyst). # 1998 Elsevier Science B.V. 0920-5861/98/$32.00 # 1998 Elsevier Science B.V. All rights reserved. P I I S 0 9 2 0 -5 8 6 1 ( 9 8 ) 0 0 0 1 3 -3