Herranz Tirma, Deng Xingyi, Cabot Andreu, Guo Jingua, Salmeron Miquel
Materials Sciences Division, Lawrence Berkeley National Laboratory, Advance Light Source, Lawrence Berkeley National Laboratory, Materials Science and Engineering Department, University of California, Berkeley, California 94720, USA.
J Phys Chem B. 2009 Aug 6;113(31):10721-7. doi: 10.1021/jp901602s.
The influence of particle size in the carbon monoxide hydrogenation reaction has been studied using cobalt nanoparticles (NPs) with narrow size distribution prepared from colloidal chemistry. The surfactant covering the NPs after synthesis could be removed by heating to 200-270 degrees C in H(2). Soft X-ray absorption spectroscopy was performed using a gas flow cell under reaction conditions of H(2) and CO at atmospheric pressure. Flow of pure hydrogen at 350 degrees C removed the protecting surfactant layer and reduced the NPs from oxidized to metallic. The NPs remained metallic during the methanation reaction with their surface covered by CO. The methanation turnover frequency of silica-supported NPs was found to decrease with diameter below 10 nm, whereas the reaction activation energy was found to be independent of NP size. H-D exchange experiments indicated that it is the dissociation of H(2) that is responsible for the observed decrease in activity with size.
利用通过胶体化学制备的具有窄尺寸分布的钴纳米颗粒（NPs），研究了粒径在一氧化碳加氢反应中的影响。合成后覆盖在NPs上的表面活性剂可通过在H₂中加热至200 - 270℃除去。在大气压下H₂和CO的反应条件下，使用气体流通池进行软X射线吸收光谱分析。在350℃的纯氢气流除去了保护表面活性剂层，并将NPs从氧化态还原为金属态。在甲烷化反应过程中，NPs保持金属态，其表面被CO覆盖。发现二氧化硅负载的NPs的甲烷化周转频率在直径低于10 nm时降低，而反应活化能与NP尺寸无关。H-D交换实验表明，正是H₂的解离导致了观察到的活性随尺寸的降低。
