Catalytic mechanism of in-situ Ni/C co-incorporation for hydrogen absorption of Mg

Ni and carbon materials exhibit remarkable catalysis for the hydriding reaction of Mg.But the underlying mechanism of Ni/C hybrid catalysis is still unclear.In this work,density functional theory(DFT)calculation is applied to investigate the effect of Ni/C co-incorporation on the hydriding reaction of Mg crystal.The morphology and crystal structure of the Ni/C co-incorporated Mg sample show that the coincorporated structure is credible.The transition state searching calculation suggests that both the incorporations of Ni and C are beneficial for the H_(2) dissociation.But Ni atom has a dramatic improvement for H_(2) dissociation and makes the H diffusion become limiting step of the hyriding reaction.The Ni dz_(2)orbit and H s orbit accept the electrons and combine together compactly,while the Ni d_(xy) orbit is half-occupied.The catalytic effect of Ni on H_(2) dissociation can be ascribed to the bridging effect of Ni d_(xy) orbit.The incorporation of C can weaken the over-strong interaction between Ni and H which hindered the H diffusion on Mg(0001).The Ni/C co-incorporated Mg(0001)shows the best performance during hyriding reaction compared with the clean and single incorporated Mg(0001).

Effects of Ce/Zr ratio on the structure and performances of Co-Ce_(1-x)Zr_xO_2 catalysts for carbon dioxide reforming of methane

The Co-incorporated Ce1-xZrxO2 catalysts were prepared by co-precipitation for carbon dioxide reforming of methane.The ratio of Ce to Zr was varied to optimize the performances of co-precipitated Co-Ce-Zr-Ox catalysts.The prepared catalysts were characterized by various physico-chemical characterization techniques including TPR,X-ray diffraction,N2 adsorption at low temperature,XPS and CO2-TPSR.The co-precipitated Co-Ce0.8Zr0.2O2 sample containing 16% CoO exhibited a higher catalytic activity among the five catalysts,and the activity was maintained without significant loss during the reaction for 60 h.Under the conditions of 750 ℃,0.1 MPa,36000 ml/（h gcat）,and CO2/CH4 molar ratio of 1：1,the CO2 conversion over this catalyst was 75% while the CH4 conversion was 67%.The cubic Ce0.8Zr0.2O2 facilitated a higher dispersion and a higher reducibility of the cobalt component,and the apparent activation energy for Co-Ce0.8Zr0.2O2 sample was 49.1 kJ/mol in the CO2/CH4 reforming reaction.As a result,the Co-Ce0.8Zr0.2O2 sample exhibited a higher activity and stability for the reforming of CH4 with CO2.