甲醛在CeO_2(110)表面的吸附

Adsorption of Formaldehyde on CeO_2( 110) Surface

利用密度泛函理论计算了甲醛在洁净CeO_2(110)表面的吸附行为,发现甲醛在表面存在化学与物理吸附。甲醛化学吸附时,甲醛的碳、氧原子分别与表面氧、铈原子发生作用,生成CH_2O_2,平面结构变为四面体构型;吸附能随覆盖度的减小而增大;电子结构分析表明,其最高占据轨道nO的电子进入表面铈原子的空轨道,形成Ce-Os化学键;而表面氧原子的电子填充到甲醛的C-Of反键轨道,形成新的C-Os键,甲醛的C-Of键长伸长。而物理吸附的甲醛,平面结构不变,吸附能较小,电子结构无明显变化。

Formaldehyde adsorption behaviors on clean CeO_2（ 110） surface were systematically investigated by density functional theory（ DFT） method. Chemisorption and physisorption configurations were obtained. For the strongly chemisorbed formaldehyde,the carbon and oxygen atoms of formaldehyde interacted with the corresponding oxygen and cerium atoms of ceria surface with the formation of dioxymethylene intermediate. The adsorption energies decreased with increasing coverage of formaldehyde,and the interactions of the adsorbed formaldehydes could be negligible until the coverage was up to 0. 25monolayer（ ML）. The density of states（ DOS） analysis indicated that the energy of the highest occupied molecular orbital（ HOMO）,nO,shifted downward greatly,while the oxygen electrons of CeO_2 surface transfered to the lowest unoccupied molecular orbital（ LUMO） of formaldehyde,π＊CO. Meanwhile,the new C- Osand Ce- Ofbonds form and the corresponding C- Ofbonds of formaldehyde were elongated. However,the physisorbed formaldehyde remained the planar structure free formaldehyde molecule with low adsorption energies,and the electron structures were slightly changed.