Theoretical Study On Hydrogen Production From Methanol Steam Reforming Catalyzed By Molybdenum Carbide-Based Catalysts

It is urgent to develop clean energy in the context of excessive energy consumption and excessive carbon emissions.Hydrogen energy is a promising alternative energy due to its green,clean and high calorific value.However,hydrogen is inconvenient for storage and transportation due to its low bulk density,which greatly limits the utilization of hydrogen.Methanol has been widely studied as a liquid organic hydrogen storage compound.Previous catalysts for methanol steam reforming for hydrogen production were mainly Cu-based catalysts and precious metal catalysts.In recent years,transition metal carbides have attracted wide attention due to their unique catalytic effect and high cost performance.Therefore,there are more and more experimental studies on the production of hydrogen from methanol steam reforming catalyzed by transition metal carbides.However,the research on its reaction mechanism is still relatively few.So in this paper,we studied the adsorption of species on Mo₂C（001）,Ni/Mo₂C（001）and Pt/Mo₂C（001）by Density Functional Theory（DFT）calculations.The reaction mechanism of methanol steam reforming for hydrogen production,the effect of loading Ni or Pt on adsorption and reaction activation energy was analyzed,and the change of the electronic properties of the catalyst surface when doping metal was studied,which further proved the synergistic effect of loading metal and catalyst surface.The details are as follows:The electronic properties of the catalyst surface were investigated by DFT calculations,and it was found that electrons would transfer from Ni and Pt to adjacent Mo atoms after loading with Ni or Pt atoms,thereby enhancing the Mo activity around Ni and Pt atoms.At the same time,the d-band electrons of Mo atoms are more localized,which improves the catalytic performance of the catalyst.The adsorption and co-adsorption of various species involved in methanol steam reforming on Mo₂C（001）,Ni/Mo₂C（001）and Pt/Mo₂C（001）surfaces,as well as related reaction energy barriers and reaction energy were systematically studied by DFT calculations.From the adsorption point of view,loading Ni and Pt atoms can affect the adsorption energy and change the stable adsorption position;it is found that hydrogen can be produced through two paths on the surfaces of the three catalysts through transition state studies.However,loading Ni and Pt atoms changes the optimal dehydrogenation sites for methanol activation to formaldehyde,and the rate-determining steps of the two pathways are different on the three surfaces.By comparing the reaction activation energy data,it is found that most of the reaction activation energies on the Ni/Mo₂C（001）and Pt/Mo₂C（001）surfaces have different degrees of reduction.It is particularly noteworthy that after loading Pt atoms,the dissociation energy barrier of water is greatly reduced on the catalyst surface,which is beneficial to promote the methanol steam reforming reaction,which can effectively improve the hydrogen yield and reduce CO of selectivity.