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Title:: CO methanation on La/Ni(111) Surface: Effect of La Electron Delocalization on Activity and Selectivity

Author(s):: ZHI Cuimei 1; ZHANG Riguang 2; WANG Baojun 2; (1. College of Chemistry and bioengineering, Taiyuan University of Science and Technology, Taiyuan, Shanxi 030021) (2. Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan, Shanxi 030024)

Keywords:: DFT; Microkinetic modeling; Differential charge density; Electron delocalization; Synergistic effect

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Abstract:: In attempting to promote the activity and selectivity of CO conversion to CH4 and simultaneously suppress CH3OH formation, density functional theory calculation has been employed to insight into reaction mechanism and the effect of the promoter La on CO conversion to CH4 on La/Ni(111). Our results indicate that the promoter La could enrich the outer layer valence electron density of Ni, make the d-band center of La/Ni(111) upward, and thereby leads to a significant increase of the reactivity. Accordingly, the enhanced activity and selectivity to CH4 as well as CH3OH resistance mainly due to the electronic effect of the promoter La on La/Ni(111), where the synergistic effect between La and Ni plays an important role. Meanwhile, the microkinetic modeling was used to estimate the production rates of CH4 and CH3OH under the experimental conditions, and the result show that r(CH4) is larger than r(CH3OH) at the same temperature, and the relative selectivity of CH4 reaches almost as high as 100% in the temperature range of 550 to 750 K, and thereby no CH3OH is formed when La is doped. Further, to clarify the effect of La promoter on CH4 formation at electron level, Bader charges and the projected density of states have been examined for CO、HCO、COH and CH2O, which are the key intermediates of Path1, Path2, Path3 and Path4 for CH4 formation, respectively. The results indicate that, it is electron transfer from La to Ni and the strong interaction between La and O that weaken the C–O bond and promote the cleavage of C?O bond, and thereby lead to no CH3OH yield, which controls the selectivity to CH4. Through the analyzing the differential charge density of La atom and its surrounding Ni atoms over La/Ni(111), the result of the direction along La→Ni of charge transfer, has been shed light on furtherly. Conclusively, La/Ni(111) shows a significant increase of the activity and selectivity to CH4 compared to Ni(111), which is mainly originated from the synergistic effect between La and Ni.

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CO methanation on La/Ni(111) Surface: Effect of La Electron Delocalization on Activity and Selectivity

MATERIALS CHINA[ISSN:1674-3962/CN:61-1473/TG]

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