前躯体浸渍法制备VO_x/Al_2O_3及其催化二甲醚制甲醛性能

Selective oxidation of dimethyl ether to formaldehyde over VO_x/Al_2O_3 catalysts prepared by modified impregnation method

采用前躯体浸渍法合成了VOx/Al2O3催化剂,并采用XRD、Uv-Vis、H2-TPR、NH3-TPD以及吡啶吸附红外等技术对催化剂材料的结构和性能进行了表征,同时考察了催化剂上二甲醚制备甲醛的反应性能。XRD的测试表明,V的氧化物在载体上处于高度分散状态,没有独立的V2O5晶相峰存在。Uv-Vis的测试表明,前躯体浸渍法制备的催化剂较之常规浸渍法制备的催化剂位于更高波数,因而VOx物种在载体表面的分散更加均一。H2-TPR的结果表明前躯体浸渍法制备的催化剂,相对更加容易还原,催化氧化能力更强。NH3-TPD以及吡啶吸附红外的结果表明前躯体浸渍法制备的催化剂相对具有较少的B酸和较弱的酸性。前躯体浸渍法制备的VOx/Al2O3催化剂在DME选择氧化制备甲醛的过程中,具有更高的甲醛的选择性和收率,选择催化的性能更佳。

VOx/Al2O3 catalysts were prepared by modified impregnation method and characterized by XRD, Uv-Vis, H2-TPR, NH3-TPD and pyridine-absorbed FT-IR techniques. The catalytic performances of the catalysts for dimethyl ether （DME） oxidation to formaldehyde were evaluated as well. The results showed that the vanadium species in the catalysts existed mainly in the form of high dispersed isolated and polymeric vanadium species and no independent V205 crystalline phase peak exited. The catalyst prepared by modified impregnation method possessed relatively higher wave in the Uv-vis spectra which meant that the vanadium species dispersed more uniformly than those prepared by conventional method; the catalysts were more easily reduced by H2 which meant that they had relatively higher oxidation activity; the catalysts possessed less Brhnsted acid and weaker acidity. The catalysts exhibited higher HCHO selectivity and yield for DME selective oxidation to formaldehyde.