材料期刊网

实验研究了溶胶凝胶法制备催化剂过程中钒元素的初始价态(V4+或V5+)对焙烧后催化剂特性的影响,并考察了催化剂在150-350℃温度范围内对1,2-二氯苯(1,2-DCBz)的催化转化效果.通过低温氮气吸附、X射线衍射(X-ray diffraction,XRD)、光电子能谱(X-ray photoelectron spectroscopy,XPS)、氢气程序升温还原(H2 Temperature programmed reduction,H2-TPR)、以及色散光谱(Energy dispersive spectroscopy,EDS)来获取催化剂的基本特性.结果表明,在催化剂制备过程中,将偏钒酸铵中的V5+还原至V4+可以有效改善焙烧后催化剂V2O5/TiO2理化特性,提高1,2-二氯苯的催化转化效率.150℃时,1,2-二氯苯转化率由43％增加至62％,而在220-350℃范围内,转化效率提升仍大于10％.这与催化剂吸附能力和氧化能力的共同增强有关.根据催化剂表征结果可知,与未还原处理的V2O5/TiO2相比,还原处理后催化剂的比表面积和总孔容分别增加了22 m2·g-1和0.09 cm3·g-1,且孔径尺寸在2-3 nm的孔容积增大.这些特性都有助于催化剂吸附能力的提升.此外,还原处理后催化剂中V的平均化合价和表面吸附氧浓度增大.V的平均化合价由4.64增大至4.72,表面吸附氧浓度由11％增大至13％,表明催化剂氧化能力增强.然而该方法对V2O5/TiO2-CNTs催化剂的催化活性影响较小.

The effect of V primary oxidation state (V4+ or V5+) during the sol-gel preparation process on the catalyst after calcine was studied,and tests of its catalytic conversion activity on 1,2-dichlorobenzene (1,2-DCBz) was also conducted in a fixed-bed catalytic reactor,operating in a range of 150-350 ℃.Several physicochemical methods,including nitrogen adsorption,X-ray diffraction (XRD),X-ray photoelectron spectroscopy (XPS),H2 temperature programmed reduction (H2-TPR) and energy dispersive spectroscopy (EDS) were employed to characterize their structures and properties.Reducing V5+ of ammonium metavanadate to V4+ effectively improved the physicochemical ability of V2O5/TiO2,and thus promoted the catalytic conversion of 1,2-DCBz.The conversion efficiency of 1,2-DCBz increased from 43％ to 62％ over pre-reduced V2O5/TiO2 at 150 ℃.In the 220-350 ℃ range,over 10％ increase of 1,2-DCBz conversion was also obtained.This is ascribed to the mutual enhancement of adsorption and oxidation ability of the catalyst.Compared with V/Ti,the specific surface area and the total pore volume increased by 22 m2· g-1 and 0.09 cm3·g-1,respectively.The pores of 2-3 nn of pre-reduced V2O5/TiO2 also evidently increased.These results indicate the improvement of adsorption ability of the catalyst.Moreover,the raised average oxidation state of vanadium from 4.64 to 4.72 and concentration of surface active oxygen from 11％ to 13％ contributed to the enhancement of oxidation ability of pre-reduced V2O5/TiO2.However,Reducing V5+ of ammonium metavanadate to V4+ had less influence upon the V/Ti-CNTs catalyst.