V2O5表面氧和晶格氧的热脱附性能

V_2O_5是一种重要的烃类选择氧化催化剂,ESR研究表明,在V_2O_5/SiO_2上存在有O~-,O~(2-)和O_3~-等物种。但是氧吸附物种的ESR研究迄今仍局限于较低温度,与实际催化反应条件尚存相当差距。用程序升温脱附(TPD)法研究,恰好能补其不足。但是关于V_2O_5表

THERMAL DESORPTION PROPERTIES OF THE SURFACE AND LATTICE OXYGEN OF V2O5

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_2Its 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.