Study On Directional Regulation Of Nitrogen-doped Activated Carbon Functional Groups For Catalytic HI Decomposition

With the rapid growth of global energy consumption,energy security,greenhouse gas emissions and air pollution and a series of other problems arise,traditional energy has been difficult to meet the basic needs of human production and life.Hydrogen energy is an important direction of China’s low-carbon energy strategy but how to make hydrogen efficiently is the core issue of hydrogen energy development.Among various methods of hydrogen production,the thermochemical sulfur iodide cycle process is able to balance the problem of balancing the efficiency of hydrogen production with the cost of hydrogen production,and is considered to be one of the most desirable methods of hydrogen production by introducing reaction intermediates to split the hydrolysis into multiple primitive reaction steps.The actual process has a very low efficiency of hydrogen iodide decomposition and requires a reduction of the reaction potential by adding a catalyst to the reaction process.After considering the cost and efficiency,the nitrogen-doped non-metallic carbon material proved to be an excellent catalyst,and the doping of nitrogen atoms resulted in an enhanced polarity of the catalyst and a significant increase in the efficiency of hydrogen iodide decomposition.However,due to the complex composition and structure of activated carbon materials,the question of which nitrogen-containing functional group substitution site is the active center for catalytic hydrogen iodide decomposition is still being explored.In this study,experimental data analysis and density flooding calculations were combined to realize the targeted substitution of nitrogencontaining functional groups to modify the unsaturated carbon sites at the edges of activated carbons,and finally to investigate which nitrogen-containing functional group is the reactive center for HI decomposition catalyzed by nitrogen-doped activated carbons.In this paper,we firstly used NH3-CO2 co-activation method to investigate the pore formation mechanism and nitrogen substitution mechanism of the co-activation method on the basis of deoxygenated hydrothermal carbonized carbon material by controlling the variables such as the ratio of NH3 and CO2,activation temperature and activation time,and initially established a set of regulatory mechanism for the targeted substitution modification of nitrogencontaining functional groups on the basis of maintaining a high level of physical property parameters of activated carbon.The samples 100N800-3h,100N800-4h and 50N800-4h contained 7.37%,7.24%and 7.79%nitrogen,respectively,and the percentage of pyridine nitrogen reached 77.28%,75.94%and 60.87%.By comparing the samples with similar physical property parameters and nitrogen content,the conclusion that the higher the ratio of pyridine to nitrogen,the higher the efficiency of HI catalytic decomposition of nitrogen-doped activated carbon was obtained.On this basis,the activated carbon was modified by using the pyridine nitrogen group 4,4’-Bipyridine as the nitrogen source,and the modulation mechanism of the nitrogen-containing functional group targeted substitution modification was complemented by modulating the activated carbon from the sequence of activation steps,the concentration of impregnation solution and the ratio of impregnation solution to activator to obtain a higher ratio of pyridine nitrogen.The percentage of pyridine nitrogen functional groups in the samples reached the peak at the bipyridine solution concentration near 0.3 g/L-0.35 g/L,while HI decomposition efficiency was also the highest in its class.In quantum chemical calculations based on density functional theory(DFT),Gauss View was used to build and optimize the active carbon sp2 hybridization model with multiple nitrogen-containing functional groups replacing the carbon sites,Gaussian was used to calculate the reaction paths of HI molecules on the edge sites of the carbon planar model,B3LYP/def2-TZVP level based on the BERNY energy gradient through the full The geometric configuration of each stationary site on the potential energy surface of the reaction with HI after the substitution of amorphous carbon sp2 hybridization planar model and various nitrogencontaining functional groups for unsaturated carbon active sites was optimized by parameter resolution,the transition state was solved and the transition state structure was confirmed by vibrational frequency analysis,and the minimum energy path(MEP)of the HI decomposition reaction catalyzed by different nitrogen-containing functional groups after the directional substitution of modified carbon planar model was calculated by intrinsic reaction coordinate(IRC)and combined with zero-point energy(ZPE)and electronic ground state energy are combined with the thermodynamic enthalpy correction to obtain the relative values of the reaction potential of the reaction process,so as to compare the ease of reaction occurrence,and finally verify the core fundamental reactions HI=H+I and HI+H=H2+I of the HI decomposition reaction catalyzed by nitrogen-doped activated carbon.The nitrogen-containing functional groups changed the mechanism of I adsorption and H stay away,where both pyridine nitrogensubstituted carbon models obtained lower activation energies in the HI decomposition reaction.The reaction potentials in the C-type carbon planes decreased by 74.64%(378.4 to 216.5 kJ/mol)compared with those in the carbon planes without substitution of the active site of the carbon atom by the nitrogen-containing functional group;the W-type carbon plane model decreased by 69.22%(355.7 to 210.2 kJ/mol);the E-type carbon plane model decreased by 62.08%(525.8 to 324.4 kJ/mol);t-type carbon plane model decreased by 42.21%(384.4 to 270.3 kJ/mol).