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选用V2O5作为催化剂,活性炭为载体,偏钒酸铵的草酸溶液为浸渍前驱体,采用等体积浸渍法制备了V2O5/C催化剂,将其应用于乙二醛的液相氧化.并对反应液用液相色谱进行了定性,在确定了催化体系中氧化产物的基础上,考察了V2O5含量和焙烧温度对催化剂催化性能的影响,利用XRD和TEM等手段对催化剂进行了表征.结果显示,V2O5含量较低时(w(V2O5)<3%),催化剂的活性组分分散度较高,乙二醛转化率和乙醛酸的选择性都随着V2O5的含量提高而逐渐增加;当负载量为3%时,催化效果最佳,乙二醛转化率和乙醛酸的选择性分别达到16.16%和76.75%;当V2O5的质量分数大于3%时,V2O5颗粒在活性炭表面发生明显聚集,V2O5开始出现多层吸附,导致乙二醛转化率和乙醛酸得率略有下降.而焙烧温度是制备负载型催化剂的一个重要影响因素.焙烧温度的作用不仅在于使活性组分的前驱体充分分解,同时也影响着活性组分的分散状态.我们考察了经不同温度焙烧后的催化剂的活性,从表征结果来看,在473K以下焙烧时,可能活性组分的前驱体未能充分分解,活性中心数目较少,反应效果较差;当V2O5负载量为3%、焙烧温度为573K时,催化剂具有较高的催化活性和选择性,反应5h,乙二醛的转化率为18.76%,乙醛酸的选择性为77.70%;而在温度升高至673K以上时,催化剂中活性组分出现了部分烧结团聚现象,导致活性中心分布不均匀,从而降低了催化活性.另外,V2O5/C催化剂重复使用3次后,乙二醛的转化率和乙醛酸的得率略有降低,催化剂显示了很好的稳定性.该法开创了钒系催化剂对有机醛类的催化氧化合成;将其应用到乙二醛的部分液相氧化中.结果表明,采用了环境友好氧气氧化剂,在比较温和的条件(常温常压)下,液相中将乙二醛氧化为乙醛酸,V2O5/C催化剂对乙二醛的氧化具有良好的催化活性和选择性,除了生成目标产物乙醛酸外,还生成少量副产物草酸.并且消除了酸催化剂带来的污染,工艺流程短,操作容易,无污染等,与贵金属催化剂相比,V2O5无需控制溶液的pH值就可得到乙醛酸,而且价格便宜,来源广泛.
V2O5 as catalyst, activated carbon as carrier and ammonium metavanadate as oxalic acid solution as impregnation precursor were prepared by the same volume impregnation method and applied to the liquid-phase oxidation of glyoxal. Liquid chromatography. The effects of V2O5 content and calcination temperature on the catalytic performance of the catalyst were investigated. The catalysts were characterized by XRD and TEM. The results showed that the content of V2O5 When the content of V2O5 is lower (w (V2O5) <3%), the active component of the catalyst has higher dispersion, the conversion of glyoxal and the selectivity of glyoxylic acid increase with the increase of V2O5 content. When the loading is 3%, the catalytic effect was the best, the conversion of glyoxal and the selectivity of glyoxylic acid reached 16.16% and 76.75% respectively. When the mass fraction of V2O5 was more than 3%, the V2O5 particles aggregated obviously on the activated carbon surface and V2O5 began The results showed that the conversion of glyoxal and the yield of glyoxylic acid decreased slightly, while the calcination temperature was an important factor in the preparation of supported catalysts.The effect of calcination temperature was not only that the precursors of the active components were fully decomposed , But also shadow The active components of the dispersed state.We investigated the activity of the catalyst after calcination at different temperatures from the characterization results, below 473K calcination, the precursor of the active ingredient may not be fully decomposed, the number of active centers less , The reaction is poor. When the loading of V2O5 is 3% and the calcination temperature is 573K, the catalyst has high catalytic activity and selectivity. The reaction time is 5h, the conversion of glyoxal is 18.76%, the selectivity of glyoxylic acid Was 77.70% .At the same time, when the temperature was above 673K, the agglomeration of the active components in the catalyst was partially sintered and resulted in the uneven distribution of the active sites and the decrease of the catalytic activity.In addition, after the V2O5 / C catalyst was reused for 3 times , The conversion of glyoxal and the yield of glyoxylic acid decreased slightly, and the catalyst showed good stability.The method initiated the catalytic oxidation of vanadium-based catalyst to organic aldehydes and applied it to glyoxal Of the liquid phase oxidation.The results show that the use of environmentally friendly oxygen oxidizer, in relatively mild conditions (normal temperature and pressure), the glyoxal in the liquid phase oxidation of glyoxal, V2O5 / C catalyst on glyoxal The oxidation has good catalytic activity Selectivity, in addition to generating the target product of glyoxylic acid, but also generate a small amount of oxalic acid by-product. And to eliminate the acid catalyst pollution, short process flow, easy operation, no pollution, compared with noble metal catalysts, V2O5 without control solution The pH value of glyoxylic acid can be obtained, but also cheap, wide range of sources.