Theoretical Study On CO₂ And N₂ Molecules Reduction Catalyzed By Doped 2D MoS₂

Heterogeneous catalytic conversion of small molecules such as CO2 and N2 into a series of beneficial chemicals has always been the focus of many researchers,and precisely designing high-efficiency catalysts by studying the mechanism of the reaction is the top priority in the research process.Density functional theory(DFT)has become an important mean of designing and studying new materials,and has played an indispensable role in the study of the catalytic mechanism of catalysts.The MoS2 layers are connected by weak van der Waals and are easily peeled off.Monolayer 2H phase MoS2 is a direct bandgap semiconductor with a bandgap of about 1.8 eV,and electrons can be directly transited from the valence band to the conduction band,which increases the electrical conductivity of the material and significantly improves its optical,electrical,and thermal catalytic activities.At the same time,because MoS2 is a nonprecious metal catalyst,it is widely used in hydrogen evolution reaction,CO2 reduction reaction and catalytic synthesis of ammonia and other reactions.Based on these,here uses DFT to study the potential applications of transition metal-doped MoS2 in CO2 hydrogenation to methanol and electrocatalytic nitrogen to ammonia reactions through detailed mechanism studies.The main contents are as follows:(1)Search for the potential non-noble metal single-atom doped MoS2 catalysts for the hydrogenation of CO2 molecule(CO2RR).Based on DFT,Ni1,Cu1,Zn1,Rh1,Pd1 and Pt1 doped MoS2 with high stability,high hydrogen adsorption and higher activity to dissociate molecular hydrogen are screened out from the twenty-six doped M1-MoS2(M=Sc1-Zn1,Y1-Cd1 and Ta1-Au1),these six doping cases are servesed as the potential catalysts toward CO2 hydrogenation into methanol.After the dissociation of gas phase H2,the hydrogenation of CO2 proceeds via CO2→*COOH→*C(OH)2→*CH(OH)2→*CHOH→*CH2OH→CH3OH pathway,the energy barriers and reaction energies of each path are calculated.While,the whole methanol formation rate is not only related to energy barrier along the pathway but also the hydrogen dissociation barrier,the coverage of different surface atomic hydrogen and the coverage of carbon-containing species.Thus,microkinetic simulations are adopted to compare the production rate of methanol on Ni1(Cu1,Zn1,Rh1,Pd1,Pt1)-MoS2 compare with that on Pt1-MoS2.At experimental condition T=483.15 K,PCO2=8 bar and PH2=24 bar,the production rates of methanol on Zn1-MoS2 and Pd1-MoS2 are promoted by 26.00 and 1.35 times,respectively.Thus,Zn1-MoS2 is the promising candidate to Pt1-MoS2 for CO2 hydrogenation to methanol with high activity and low cost,microkinetic analysis also provides more accurate guidance for the screening of catalysts.(2)A detailed study of the electrocatalytic nitrogen-to-ammonia reaction(eNRR)on Fe-doped MoS2 is carried out to reveal the regulation mechanism of the synergistic effect on activity and selectivity.Based on DFT calculations,the eNRR activity and selectivity on 2D MoS2 doped with Fe single atoms in different forms(loading,substitution,etc.)are systematically studied.Based on the single-atom doping with the best performance,the effect of co-doping of Fe and O is studied.The results show that the eNRR activity of MoS2 with Fe and O co-doped Mo-edge structure is higher than that of MoS2 with planar and S-edge structure.The synergetic effect between single Fe atom and the directly bonded oxygen atoms in Mo-edge of MoS2(Fe1-1O,2O,3O,4O@Mo-edge-MoS2)actually works for the high-performance of NRR.And the modest charge transfer between Fe and support in Fe1-1O,2O,3O,4O@Mo-edgeMoS2 will greatly promote the NRR activity and selectivity.The Fe1-4O@Mo-edgeMoS2 presents the highest activity and selectivity during the electrochemical environment.Thus,modulating the oxygen coordination of single Fe atom to a modest level will greatly increase the eNRR performance.(3)High-throughput screening of a series of transition metal-doped MoS2 towards eNRR is used to obtain the better catalysts.Based on DFT,the catalytic performance of a series of transition metal atoms(M)doped Mo-edge of MoS2 is systematically studied.Three screening strategies are proposed based on the synthesized and validated Fe1@Mo-edge,whose limiting-potential(UL,NRR)is-0.34 V:(1)screening out the catalysts with the first protonation reaction free energy of adsorbed nitrogen molecules lower than 0.34 eV;(2)calculate the free energy profile in the eNRR process on the catalysts screened in the first step,determine the reaction free energy(ΔGPDS)of the potential-determining step,and screen out the catalysts with ΔGPDS lower than 0.34 eV;(3)the selectivity study of the catalysts screened in the second step is carried out,and the catalysts with higher selectivity than Fe1@Mo-edge were screened out.Finally,it is found that Ru1,Re3,4 and Os1 doped Mo-edge of MoS2(Ru1,Re3,4,Os1,Pt1@Mo-edge)had the improved NRR catalytic activity with UL,NRR of-0.27,-0.19,-0.20,-0.24 V and-0.27 V,respectively.Especially,increasing the loading of Re atom to Re4@Mo-edge will greatly increase the activity and selectivity.It is suggested that the activity of N2 reduction on MoS2 can be efficiently tuned by changing the doped atoms and the loading capacity of doped atoms.