二氧化钛负载的镍氧化态对乙腈气相加氢的影响

摘要

Nickel catalysts supported on TiO2 were prepared using an impregnation method. Changes in the reduction temperature from 200 to 400 °C resulted in dispersion of nickel with different oxidation states on TiO2. The gas-phase hydrogenation of acetonitrile was found to be influenced by the nickel oxidation state. Nickel reduced at 300 °C gave the highest acetonitrile conversion ratio, i.e., about 100%, when the reaction temperature was 100 °C. The product yields depend on the amount of acidic sites on Ni/TiO2 catalysts;this can be influenced not only by the TiO2 support, but also by the properties of the supported nickel nanoparticles. The triethylamine yield increased to a maximum (from 34% to about 48%) with increasing reduction temperature; this corresponded to the gradual appearance of Ni0 in Ni/TiO2 and a decrease in the intrinsic acidity of the Ni/TiO2 catalyst. Triethylamine was the initial product in the hydrogenation of acetonitrile with Ni/TiO2. The oxidation state of nickel influenced not only the conversion of acetonitrile but also desorption of the final products. A mechanism for the first step in this reaction is proposed.%采用浸渍法制备了二氧化钛负载镍催化剂。通过控制还原温度(200-400°C),在TiO2上得到不同氧化态的镍颗粒。结果发现,乙腈气相加氢反应受镍氧化态的影响,300°C下还原的催化剂表现出最高的乙腈转化活性,100°C时将乙腈完全转化。产物产率受到Ni/TiO2催化剂酸性的影响,而催化剂的酸性不仅受到TiO2载体的影响,还受到负载物Ni颗粒性质的影响。随着催化剂还原温度升高,金属态镍逐渐出现在催化剂表面,降低了催化剂的酸性强度,使三乙胺的最大产率升高(从34%升高到48%左右)。研究还发现在Ni/TiO2催化乙腈加氢反应中,三乙胺是初始产物。 Ni的状态不仅影响乙腈的转化,还影响产物的脱附。提出了乙腈加氢的第一步反应机理。