The First-Principles Study Of CO?NO Adsorption On Ni(110) Surface

In recent years,the surface catalytic reaction mechanism has attracted much attention.With the development of various surface analysis methods,the experimental researches on the surface catalysis have yielded remarkable results.The research on gas-solid heterogeneous catalysis has become a hot topic,including the exploration of catalytic reaction mechanism,the improvement of catalytic efficiency and the design of novel catalysts.Among the various catalysts,the transition metal(TM)has a unique d-orbital structure,specific catalytic activity and stability,therefore the elemental TM and the TM-oxide have been widely utilized in catalysis.However,numerous questions still remain in understanding the catalytic reaction mechanism,which hinders the further improvement of their catalytic efficiency and design of more efficient catalysts.Therefore,the study of the gas catalytic reaction mechanism on the TM/TM-oxide surface is important.In these catalytic reactions,the adsorption of gas molecules on the TM/TM-oxide surface is a prerequisite of the catalytic reaction.Therefore,the theoretical and experimental studies of the adsorption structure of gas molecules and the interaction between the gas and the TM/TM-oxide surface is important for the understanding of gas catalysis reaction mechanism.Using the first-principles calculation method based on density functional theory,the adsorption structure and vibration frequency of CO and NO molecules on Ni(110)surface and CO molecules on(2×1)Ni-O/Ni(110)surface have been studied.The calculated results have been compared with the ones given by the ultra-high vacuum Fourier transform infrared spectroscopy(UHV-FTIR)measurements.Our results show that CO molecules prefer to be adsorbed on the short-bridge site of Ni(110)surface,and the adsorption energy gradually decreases with increasing the coverage.When the coverage is higher than 0.5 ML,the orientation of CO begins to tilt to the Ni(110)surface due to the repulsion between CO molecules.The molecular vibration frequency shows the tendency of blue shift(105 cm-1 higher than the low coverage case),in agreement with the experimental observations of 103 cm-1.NO is mainly adsorbed on the short-bridge position and the top position of the Ni(110)surface,and the adsorption energy is higher than that of the short-bridge position.When the coverage is increased from 0.25 ML to 1 ML,the adsorption energy of both sites decreases.The increase of the vibration frequency of NO on the short-bridge site is 98 cm-1,consistent with the 87 cm-1 observed by UHV-FTIR.The increment of vibration frequency corresponding to the NO on the top site is 61 cm-1,which is fairly in agreement with the experimental observation(49 cm-1).The NO adsorbed on the surface of Ni(110)may be decomposed into nitrogen and oxygen atoms.The adsorption of N atom at the long bridge site of Ni(110)surface is the most stable while the three-fold hollow site is identified for the O atom.When 1 ML of NO adsorbs at the short-bridge sites near the N atom,the calculated vibrational frequency is 1787 cm-1.When 0.75 ML of NO adsorbs at the short-bridge site neighbor the O atom,the calculated result is 1744 cm-1.Such results may explain the origin of the absorption peak at the 1746 cm-1 position observed by UHV-FTIR measurement.For the(2×1)Ni-O/Ni(110)surface,CO molecules are adsorbed at the top site of the Ni atom of the Ni-O rows and form a chain-like adsorption configuration along the[110]direction.The formation of such configuration may be due to the reduction of strain of Ni-O rows.Our calculated results reveal a more stable adsorption configuration:the short-bridge site between the Ni atoms of the neighboring Ni-O atomic column.The calculated vibrational frequency is lower than that of the top-site adsorption configuration.Such results are consistent with the formation of new band observed by UHV-FTIR.