Three individual peaks of thermal solid-state reaction processes of the synthesized Mn0.90Co0.05Mg0.05HPO4?3H2O were observed corresponding to dehydration I,dehydration II and polycondensation processes.An alternative...Three individual peaks of thermal solid-state reaction processes of the synthesized Mn0.90Co0.05Mg0.05HPO4?3H2O were observed corresponding to dehydration I,dehydration II and polycondensation processes.An alternative method for the calculation of the extent of conversion was proposed from the peak area of the individual DTG peak after applying the best fitting deconvolution function(Frazer–Suzuki function).An iterative integral isoconversional equation was used to compute the values of the apparent activation energy Eαand they were found to be 65.87,78.16 and 119.32 kJ/mol for three peaks,respectively.Each individual peak was guaranteed to be a single-step kinetic system with its unique kinetic parameters.The reaction mechanism functions were selected by the comparison between experimental and model plots.The results show that the first,second and final individual peaks were two-dimensional diffusion of spherical symmetry(D2),three-dimensional diffusion of spherical symmetry(D3)and contracting cylinder(cylindrical symmetry,R2)mechanisms.Pre-exponential factor values of 3.91×106,1.35×107 and 2.15×107 s?1 were calculated from the Eαvalues and reaction mechanisms.The corresponded standard thermodynamic functions of the transition-state(activated)complexes were determined and found to agree well with the experimental data.展开更多
This paper studies the time asymptotic behavior of solutions for a nonlinear convection diffusion reaction equation in one dimension.First,the pointwise estimates of solutions are obtained,furthermore,we obtain the op...This paper studies the time asymptotic behavior of solutions for a nonlinear convection diffusion reaction equation in one dimension.First,the pointwise estimates of solutions are obtained,furthermore,we obtain the optimal Lp,1≤ p ≤ ＋∞,convergence rate of solutions for small initial data.Then we establish the local existence of solutions,the blow up criterion and the sufficient condition to ensure the nonnegativity of solutions for large initial data.Our approach is based on the detailed analysis of the Green function of the linearized equation and some energy estimates.展开更多
The analytical potential energy function of HDO is constructed at first using the many-body expansion method. The reaction dynamics of O＋HD （v = 0, j = 0） in five product channels are all studied by quasi-classical...The analytical potential energy function of HDO is constructed at first using the many-body expansion method. The reaction dynamics of O＋HD （v = 0, j = 0） in five product channels are all studied by quasi-classical trajectory （QCT） method. The results show that the long-lived complex compound HDO is the dominant product at low collision energy. With increasing collision energy, O＋HD → OH＋D and O＋HD → OD＋H exchange reactions will occur with remarkable characteristics, such as near threshold energies, different reaction probabilities, and different reaction cross sections, implying the isotopic effect between H and D. With further increasing collision energy （e.g., up to 502.08 kJ/mol）, O＋HD → O＋H＋D will occur and induce the complete dissociation into single O, H, and D atoms.展开更多
Metal-nitrogen-carbon catalysts(M-N-C)with single-atom active site are highly efficient catalysts for electrochemical CO_(2)reduction reactions(CO_(2)RR).Abundant M-N-C catalysts have been developed,and the coordinate...Metal-nitrogen-carbon catalysts(M-N-C)with single-atom active site are highly efficient catalysts for electrochemical CO_(2)reduction reactions(CO_(2)RR).Abundant M-N-C catalysts have been developed,and the coordinated adjacent nitrogen atoms as first-shell environment have been the focus of research of activity-tuning.However,the effect of second-shell carbon environment around the metal-nitrogen moiety is still unclear.Moreover,it is confusing for the discrepancy between the experimental onset potential of around–0.2 V(vs.reversible hydrogen electrode,RHE,unless otherwise noted)and theoretical predictions of–0.5 V or higher by the widely-used computational hydrogen electrode(CHE)model.Herein,using the explicit solvent model and constant potential method(CPM),the electrochemical interface on Fe-N-C is simulated for CO_(2)RR.It reveals that the*COOH formation is facilitated in water solvent environment,while the CO_(2)adsorption is potential-dependent.The predicted onset potential of around–0.2 V on Fe-N-C is consistent with experimental results.The sp2 non-hexatomic defects introduced into second-shell carbon environment are significantly influential for the CO_(2)RR.The double five-seven ring(5577)defect is the most active,compared to that with triple five-seven ring(55577)or five-eight ring(58)defects.The highly flexible structure and altered density of states of Fe site induced by 5775 defects are key to CO_(2)adsorption.This study provides new insights into the role of second-shell carbon environment for effective CO_(2)RR,and underlines the importance of CPM and solvent environment in accurate simulation for electrochemical interface.展开更多
The development of sustainable and efficient catalytic systems for the formation C-C,C-N,C-o bonds is a fundamental goal in modern synthetic chemistry.We present a biomass-derived Cu/Chitosan-800 catalyst that facilit...The development of sustainable and efficient catalytic systems for the formation C-C,C-N,C-o bonds is a fundamental goal in modern synthetic chemistry.We present a biomass-derived Cu/Chitosan-800 catalyst that facilitates a range of carbenoid insertion reactions into C-H,N-H,and O-H bonds.This catalyst demonstrates remarkable activity,enabling the functionalization of diverse substrates,including the late-stage modification of drug molecules with up to 95%yield and good recyclability.Our findings highlight the catalyst's potential in advancing environmentally friendly chemical transformations,offering a promising tool for pharmaceutical synthesis and organic synthesis.展开更多
基金supported by King Mongkut’s Institute of Technology Ladkrabang [KREF146001]
文摘Three individual peaks of thermal solid-state reaction processes of the synthesized Mn0.90Co0.05Mg0.05HPO4?3H2O were observed corresponding to dehydration I,dehydration II and polycondensation processes.An alternative method for the calculation of the extent of conversion was proposed from the peak area of the individual DTG peak after applying the best fitting deconvolution function(Frazer–Suzuki function).An iterative integral isoconversional equation was used to compute the values of the apparent activation energy Eαand they were found to be 65.87,78.16 and 119.32 kJ/mol for three peaks,respectively.Each individual peak was guaranteed to be a single-step kinetic system with its unique kinetic parameters.The reaction mechanism functions were selected by the comparison between experimental and model plots.The results show that the first,second and final individual peaks were two-dimensional diffusion of spherical symmetry(D2),three-dimensional diffusion of spherical symmetry(D3)and contracting cylinder(cylindrical symmetry,R2)mechanisms.Pre-exponential factor values of 3.91×106,1.35×107 and 2.15×107 s?1 were calculated from the Eαvalues and reaction mechanisms.The corresponded standard thermodynamic functions of the transition-state(activated)complexes were determined and found to agree well with the experimental data.
文摘This paper studies the time asymptotic behavior of solutions for a nonlinear convection diffusion reaction equation in one dimension.First,the pointwise estimates of solutions are obtained,furthermore,we obtain the optimal Lp,1≤ p ≤ ＋∞,convergence rate of solutions for small initial data.Then we establish the local existence of solutions,the blow up criterion and the sufficient condition to ensure the nonnegativity of solutions for large initial data.Our approach is based on the detailed analysis of the Green function of the linearized equation and some energy estimates.
基金Project supported by the National Natural Science Foundation of China (Grant No 10676022)
文摘The analytical potential energy function of HDO is constructed at first using the many-body expansion method. The reaction dynamics of O＋HD （v = 0, j = 0） in five product channels are all studied by quasi-classical trajectory （QCT） method. The results show that the long-lived complex compound HDO is the dominant product at low collision energy. With increasing collision energy, O＋HD → OH＋D and O＋HD → OD＋H exchange reactions will occur with remarkable characteristics, such as near threshold energies, different reaction probabilities, and different reaction cross sections, implying the isotopic effect between H and D. With further increasing collision energy （e.g., up to 502.08 kJ/mol）, O＋HD → O＋H＋D will occur and induce the complete dissociation into single O, H, and D atoms.
文摘Metal-nitrogen-carbon catalysts(M-N-C)with single-atom active site are highly efficient catalysts for electrochemical CO_(2)reduction reactions(CO_(2)RR).Abundant M-N-C catalysts have been developed,and the coordinated adjacent nitrogen atoms as first-shell environment have been the focus of research of activity-tuning.However,the effect of second-shell carbon environment around the metal-nitrogen moiety is still unclear.Moreover,it is confusing for the discrepancy between the experimental onset potential of around–0.2 V(vs.reversible hydrogen electrode,RHE,unless otherwise noted)and theoretical predictions of–0.5 V or higher by the widely-used computational hydrogen electrode(CHE)model.Herein,using the explicit solvent model and constant potential method(CPM),the electrochemical interface on Fe-N-C is simulated for CO_(2)RR.It reveals that the*COOH formation is facilitated in water solvent environment,while the CO_(2)adsorption is potential-dependent.The predicted onset potential of around–0.2 V on Fe-N-C is consistent with experimental results.The sp2 non-hexatomic defects introduced into second-shell carbon environment are significantly influential for the CO_(2)RR.The double five-seven ring(5577)defect is the most active,compared to that with triple five-seven ring(55577)or five-eight ring(58)defects.The highly flexible structure and altered density of states of Fe site induced by 5775 defects are key to CO_(2)adsorption.This study provides new insights into the role of second-shell carbon environment for effective CO_(2)RR,and underlines the importance of CPM and solvent environment in accurate simulation for electrochemical interface.
基金supported by the National Natural Science Foundation of China(22371083,22001086)the Fundamental Research Funds for the Central Universities(2024BRB003,HUST 2020kfyXJJS094)+1 种基金the State Key Laboratory of Natural and Biomimetic Drugs,Peking University(K202409)the Innovation and Talent Recruitment Base of New Energy Chemistry and Device(B21003).
文摘The development of sustainable and efficient catalytic systems for the formation C-C,C-N,C-o bonds is a fundamental goal in modern synthetic chemistry.We present a biomass-derived Cu/Chitosan-800 catalyst that facilitates a range of carbenoid insertion reactions into C-H,N-H,and O-H bonds.This catalyst demonstrates remarkable activity,enabling the functionalization of diverse substrates,including the late-stage modification of drug molecules with up to 95%yield and good recyclability.Our findings highlight the catalyst's potential in advancing environmentally friendly chemical transformations,offering a promising tool for pharmaceutical synthesis and organic synthesis.
