二氧化钛负载的镍氧化态对乙腈气相加氢的影响

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 ℃), 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 ℃下还原的催化剂表现出最高的乙腈转化活性, 100 ℃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.

Influence of Oxidation State of Nickel Supported on TiO2 on Gas-Phase Hydrogenation of Acetonitrile

Nickel catalysts supported on TiO₂ were prepared using an impregnation method. Changes in the reduction temperature from 200 to 400 ℃ 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 ℃ gave the highest acetonitrile conversion ratio, i.e., about 100%, when the reaction temperature was 100 ℃. 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. Amechanism for the first step in this reaction is proposed.