Abstract:

The existence of the surface and the lattice oxygen of V_2O_5 has been investigated by the temperature programmed desorption-mass spectrography (TPD-MS) technique. Four peaks were recorded for a TPD-MS run. They are tentatively assigned to be the adsorbed oxygen (Ⅰ, Ⅱ), the surface lattice oxygen (Ⅲ), and the lattice oxygen in the bulk. The ratio of the oxygen of peak Ⅳ to all of the oxygen in V_2O_5 (see Table 1 ) is 0.20 which implies that the lattice oxygen in the bulk of V_2O_5 desorbes according to the reaction:
V_2O_5→V_2O_4+1/2O_2
Its activation energy of desorption E_d is 217 kJ.mol~(-1) with a pre-exponential factor A=2.3×10~8 s~(-1) (2nd order). On the contrary, the E_d and A for peak III are 386 kJ.mol~(-1) and 1.4×10~(23) s~(-1) (1st order), respectively.
The difference between our TPD result and that of the references [4,3] has been discussed.