Department of Chemistry, Texas A and M University, PO Box 30012, College Station, TX 77842-3012, USA.
Proc Natl Acad Sci U S A. 2011 Jan 18;108(3):931-6. doi: 10.1073/pnas.1006635107. Epub 2010 Oct 14.
C(2)H(4)/CO/H(2) reaction is investigated on Rh/SiO(2) model catalyst surfaces. Kinetic reactivity and infrared spectroscopic measurements are investigated as a function of Rh particle size under near atmospheric reaction conditions. Results show that propionaldehyde turnover frequency (TOF) (CO insertion pathway) exhibits a maximum activity near <d(p)> = 2.5 nm. Polarization modulation infrared reflection absorption spectroscopy under CO and reaction (C(2)H(4)/CO/H(2)) conditions indicate the presence of Rh carbonyl species (Rh(CO)(2), Rh(CO)H) on small Rh particles, whereas larger particles appear resistant to dispersion and carbonyl formation. Combined these observations suggest the observed particle size dependence for propionaldehyde production via CO insertion is driven by two factors: (i) an increase in propionaldehyde formation on undercoordinated Rh sites and (ii) creation of carbonyl hydride species (Rh(CO)H)) on smaller Rh particles, whose presence correlates with the lower activity for propionaldehyde formation for <d(p)> < 2.5 nm.
在 Rh/SiO(2) 模型催化剂表面上研究了 C(2)H(4)/CO/H(2) 反应。在接近大气反应条件下，研究了 Rh 颗粒尺寸对反应动力学活性和红外光谱测量的影响。结果表明，丙醛的转化频率（TOF）（CO 插入途径）在<d(p)>≈2.5nm 附近表现出最大活性。在 CO 和反应（C(2)H(4)/CO/H(2)）条件下的偏振调制红外反射吸收光谱表明，在小 Rh 颗粒上存在 Rh 羰基物种（Rh(CO)(2)、Rh(CO)H），而较大的颗粒似乎难以分散和形成羰基。综合这些观察结果表明，通过 CO 插入生成丙醛的观察到的颗粒尺寸依赖性由两个因素驱动：（i）在配位不足的 Rh 位上丙醛生成的增加，以及（ii）在较小的 Rh 颗粒上形成羰基氢化物物种（Rh(CO)H），其存在与丙醛形成的较低活性相关<d(p)<2.5nm。
