CO吸附和加氢反应过程的原位高压MAS NMR研究

应用原位变温高压MAS核磁共振技术,对比研究了CO在不同Rh基催化剂上的吸附和加氢反应过程.29Si MAS NMR研究结果表明:Rh基催化剂中加入金属助剂后,载体Silicate-1上的表面硅羟基减少,助剂金属与硅羟基作用锚锭在载体表面.13C MAS NMR研究结果表明:当引入CO/H2混合气后,在Rh/Silicate-1催化剂上只能观测到气相CO、线式吸附CO和孪式吸附CO的快速交换信号;而在Rh-Mn/Silicate-1和Rh-Mn-Li/Silicate-1催化剂上,还观测到了倾斜式吸附的CO共振信号,表明助剂Mn或Mn-Li的加入促进了CO的吸附.随着反应温度升高,CO/H2在Rh/Silicate-1催化剂上转化生成CO2,进一步升高温度会有CH4生成;而CO/H2在RhMnLi/Silicate-1催化剂上反应活性更高,在较低的温度下就会转化生成CO2,但未观测到甲烷的生成.1H MAS NMR谱显示,反应后载体Silicate-1上硅羟基的量会减少,表明CO与载体部分表面硅羟基反应生成了CO2.

An In situ High-Pressure MAS NMR Study of the Adsorption and Hydrogenation Processes of CO

The adsorption and hydrogenation processes of CO on Rh-based catalyst were studied by in situ high-pressure (HP) MAS NMR techniques under batch-like conditions. ²⁹Si MAS NMR spectra showed that the silanol concentrations of the support Silicate-1 were reduced after impregnation of metal species. After introduction of ¹³CO/H₂ below 200 ℃, only the average exchanged signal of CO between gaseous CO, linearly adsorbed CO and dicarbonyl adsorbed CO was observed on Rh/Silicate-1; while the titled adsorbed CO appeared on Rh-Mn/Silicate-1 or Rh-Mn-Li/Silicate-1. So, the addition of Mn or Mn Li could enhance the CO adsorption. Under batch like condition, high-pressure ¹³C MAS NMR showed that the CO/H₂ reactants could only be converted to CO₂ and CH₄ on Rh/Silicate-1, while only CO2 appeared on Rh-Mn-Li/Silicate-1 at relatively lower temperatures. Meanwhile, ¹H MAS NMR showed the obvious decrease of silanol groups after reaction that indicated CO could react with silanol groups to produce CO₂.