The Study Of Nitrogen Adsorption And Reduction Mechanism On Metal-doped Cerium Dioxide By DFT

Ammonia(NH3),as a future carrier of renewable energy and a source of fertilizer in agriculture,is the key aspects and anticipated stages in promising technologies for decades,which has the characteristics of high hydrogen content and high energy density.The traditional Haber Bosch process for industrial synthesis of NH3 is energy intensive and highly dependent on fossil fuels.However,the large-scale use of fossil fuels makes the Haber Bosch process deviate from the pursuit of "carbon neutrality" in today’s society.The electrochemical reduction of N2 or no to NH3(NRR or NORR)is an attractive alternative method using green energy generated from renewable energy.However,the electrocatalytic NRR(NORR)reaction involves many electrons transfer related hydrogenation processes and has a high energy activation barrier,resulting in a slow reaction rate.Therefore,it is of great significance to develop electrocatalysts with high activity and selectivity.Herein,to be specific,for nitrogen and nitric oxide molecule,we discuss briefly the situation of Vo on pure and reduced cerium(doping partial transition metals and rare metals)and studied the application of M-doped CeO2(111)(M=Ca,Ti,V,Cr,Mn,Fe,Co,Ni,Cu and Zn)with different types of Vo as single-atom-catalysts(SAC)in NRR and NORR processes by the spin-polarized density functional theory calculations(DFT+U),and the main results are as follows:(1)Doping TMs can promote the formation of oxygen defects,apart from Ti and V-dopant due to the O atoms are easier to escape connecting to M atoms than the ones of adjacent atoms connecting to the Ce.And the value of Vo formation energies decreases as the TMs radius decrease.(2)Our computational results show that Cr-doped,Mn-doped,Fe-doped and Co-doped CeO2(111)adsorbs N2 strongly than stoichiometric surface and other M-doped CeO2 surfaces with adsorption energies of-0.82,-1.02,-0.83 and-1.05 eV.Through COHP analysis,it is found that the predicted active sites have good catalytic performance.(3)Over the surface of La-doped CeO2(111)with Vo,the Eads of-1.12 eV with horizontal adsorption of NO and the Bader charge of N increasing of 0.53 |e| and O increasing of 0.17 |e| at the most active site of reduction-Vo predicted.(4)The catalyst formed by La atom replacing Ce atom on CeO2(111)surface with Vo exhibits excellent catalytic activity for NORR,which the optimal reaction path is:NO→*NO→*NHO→*NHOH→*NHOH→*NH2+*OH→*NH3→NH3.And it is worth noting that the △G of NORR(NO reduction reaction)shows good performance to synthesize ammonia and water at room temperature in the theoretical calculation.The ammonia is formed through*NHO intermediate with an onset potential of-0.62 eV,and the low energy barrier along the lowest energy pathway,that is NO+5(H++e-)→NH3+H2O,which has a significant inhibitory effect on competition hydrogen evolution reaction(HER).