The Catalysis Of H2on Transition Metal-doped Al (111) Surfaces

For a long time, people expect to find the material with good kinetics mechanismfor hydrogen release and adsorption to storage a large amount of hydrogen byexperimental and theoretical calculation. On the other hand, people also hope todevelop better catalytic materials for re/dehydrogenation to meet the needs forchemical processing. There have been reported that the hydrogen storage propertiesare significantly improved by introducing Ti catalyst in metal hydride, especially forNaAlH4. It is found that not only the kinetics of hydrogen release and uptake isenhanced, but also the reaction becomes reversible. Essentially, the role of transitionmetals such as Ti which can improve hydrogen uptake and releasing of NaAlH4is stillambiguous and controversial. In this context, we have performed calculations basedon density-functional theory (DFT) with a plane-wave basis as implemented in theVienna ab initio Simulation Package to understanding H2adsorption anddecomposition on the Al(111) surface doped by transition metal. With the results ofthe adsorb energy, the energy barrier, the reaction path, and the migration path, wecan well understand the catalytic performance of the surface doped by differenttransition-metal. Our works include:(i) We have studied the release and uptake of hydrogen as well as the migrationsof hydrogen atoms on the Al(111)surface doped by1to3Ti atoms. The reaction ofre/dehydrogenation on Al(111) surface doped with1to3Ti atoms are investigated.Our theoretical calculations show that the reaction are feasible whatever Ti atoms areadsorbed on Al(111) surface or in place of Al atoms formed Ti-Al(111surfaces. Fromthe calculation results, the catalytic effect on the doped surface is enhanced whenincreasing the quantity of doped Ti atoms. The most interesting thing is that we foundthe reaction energy barrier is almost about zero for the formation of Ti island. H atomcan diffuse away from the suction position obtained Ti atom to other locations byovercoming relatively small energy barrier. The low energy costs for activating boththe H2splitting and the H atomic diffusion show improved catalytic performances, Tidoped Al(111) surface have showed significant catalytic hydrogenation effect.(ii) We studied the H2dissociation on the Al(111) surface doped with transitionmetal elements including Sc, V, Fe, Ti, Pt, etc. The result showed that Sc, V, Fe, Ti-doped surface could serve as a catalyst for the hydrogen dissociation. Our resultsshow that the activation energy barrier for the dissociation of H2is0.54eV,0.29eV, 0.51eV for Sc, V, Ti doped Al(111) surface, respectively. And diffusion barrier fromthe M-Al-Al to Al-Al-Al is0.51eV,0.66eV,0.57eV. The catalytic effect of Sc and Ti-doped Al (111) surface is very close for both catalytic the H2dissociation and H atomdiffusion effects. The low energy barrier of H2on the V–doped Al (111) surfacesuggests the significant catalytic effect while V and H atoms form of stronginteractions, though; it is realizable for H moving on the surface. Meanwhile, thetransition metal in the Al surface is tend to be isolated distribution, the catalyticproperties of dopant atoms only reflected the effect of the isolated transition metalatom.