V2O5/TiO2催化剂表面结构FT-IR发射光谱研究(II)

用傅里哀变换红外发射光谱原位考察了V_2O_5/TiO_2催化剂在制备焙烧过程中担载偏钒酸铵的热分解步骤及其形成的表面活性相结构。偏钒酸铵在200 ℃左右分解, 在300 ℃之前完全转化为晶相V_2O_5。担载于TiO_2上的偏钒酸铵在100 ℃左右与TiO_2已产生强的化学作用, 在200 ℃之前已完全分解。对于10%(质量分数)V_2O_5/TiO_2催化剂其担载偏钒酸分解后在1020 cm~(-1)附近出现晶相V_2O_5的特征峰。但在500 ℃进一步焙烧后晶相V_5O_5的峰减弱并在1025—900 cm~(-1)区出现宽峰, 表明部分晶相V_2O_5可能转化为二维高分散的VO_x物种。2%(质量分数)V_2O_5/TiO_2催化剂在焙烧过程中也显示晶相V_2O_5的弱峰, 但同时也观察到属于VO_x物种的宽峰。进一步降低钒担载量, V_2O_5晶相特征峰逐渐消失, 而在1025—900 cm~(-1)区出现二维VO_x物种的宽峰。结果还表明傅里哀变换红外发射光谱是表征氧化物催化剂表面相结构的一种有力的方法。

FT-IR Emission Spectroscopic Studies of Surface Structure of V2O5/TiO2 Catalyst

FT-IR emission spectroscopy has been used to study the surface structure of V_2O_5/TiO_2 catalyst with V_2O_5 loadings of 0.4%, 2% and 10% wt. prepared by impregnation of TiO_2 in NH_4VO_3 solution. The IR emission spectra were recorded insitu durinbg the course of a calcination of the impregnated catalyst from 100 ℃ to 500 ℃. The ammonium vanadate supported on TiO_2 was found to be decomposition more easily than pure NH_4VO_3 most possibly owing to the chemical interaction between vanadate and TiO_2. For 10%. wt. V_2O_5/TiO_2 catalyst the IR peaks due to V_2O_5 phase appeared as the catalyst was calcined at 200-400 ℃. When the catalyst was calcined at 500 ℃ the peaks of V_2O_5 phase were evidently reduced indicating that the part of V_2O_5 phase decreased and a broad peak ranging from 1050 cm~(-1) to 900 cm~(-1) became prominednt especially after a calcination at 500 ℃. The broad peak was tentatively assigned to the highly dispersed VO_x species which might be the two-dimensional vanadium oxide. This study also demonstrated that FT-IR emission spectroscopy is a very sensitive technique for investigating the surface structure of metal oxide catalyst.