College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan, 030024, PR China.
Chemphyschem. 2013 Jan 14;14(1):204-12. doi: 10.1002/cphc.201200807. Epub 2012 Nov 23.
The reaction mechanism of CO oxidation on the Co(3)O(4) (110) and Co(3)O(4) (111) surfaces is investigated by means of spin-polarized density functional theory (DFT) within the GGA+U framework. Adsorption situation and complete reaction cycles for CO oxidation are clarified. The results indicate that 1) the U value can affect the calculated energetic result significantly, not only the absolute adsorption energy but also the trend in adsorption energy; 2) CO can directly react with surface lattice oxygen atoms (O(2f)/O(3f)) to form CO(2) via the Mars-van Krevelen reaction mechanism on both (110)-B and (111)-B; 3) pre-adsorbed molecular O(2) can enhance CO oxidation through the channel in which it directly reacts with molecular CO to form CO(2) [O(2)(a)+CO(g)→CO(2)(g)+O(a)] on (110)-A/(111)-A; 4) CO oxidation is a structure-sensitive reaction, and the activation energy of CO oxidation follows the order of Co(3)O(4) (111)-A(0.78 eV)>Co(3)O(4) (111)-B (0.68 eV)>Co(3)O(4) (110)-A (0.51 eV)>Co(3)O(4) (110)-B (0.41 eV), that is, the (110) surface shows higher reactivity for CO oxidation than the (111) surface; 5) in addition to the O(2f), it was also found that Co(3+) is more active than Co(2+), so both O(2f) and Co(3+) control the catalytic activity of CO oxidation on Co(3)O(4), as opposed to a previous DFT study which concluded that either Co(3+) or O(2f) is the active site.
采用 GGA+U 方法，在 spin-polarized density functional theory（DFT）框架下，研究了 CO 在 Co(3)O(4)（110）和 Co(3)O(4)（111）表面上氧化的反应机理。阐明了 CO 氧化的吸附情况和完整反应循环。结果表明：1）U 值不仅会影响绝对吸附能，还会影响吸附能的趋势，从而显著影响计算出的能量结果；2）CO 可以通过 Mars-van Krevelen 反应机制，直接与表面晶格氧原子（O(2f)/O(3f)）反应生成 CO(2)；3）预吸附的分子 O(2)可以通过直接与分子 CO 反应形成 CO(2) [O(2)(a)+CO(g)→CO(2)(g)+O(a)]的通道，增强 CO 氧化，这种通道存在于（110）-A/（111）-A 上；4）CO 氧化是一个结构敏感的反应，CO 氧化的活化能遵循 Co(3)O(4)（111）-A（0.78 eV）>Co(3)O(4)（111）-B（0.68 eV）>Co(3)O(4)（110）-A（0.51 eV）>Co(3)O(4)（110）-B（0.41 eV）的顺序，即（110）表面对 CO 氧化的反应性高于（111）表面；5）除了 O(2f)，还发现 Co(3+)比 Co(2+)更活跃，因此 O(2f)和 Co(3+)都控制着 Co(3)O(4)上 CO 氧化的催化活性，与之前的 DFT 研究相反，该研究认为要么是 Co(3+)要么是 O(2f)是活性位。
