Theoretical Calculations On Gas Adsorption In Porous Carbon Material And Acidity In Beta Zeolite

Carbon material and Beta zeolite are very important in applications. Porous carbon material exhibits excellent performance in CO2 adsorption as a novel functional material. Besides, more attention has been put into the the detailed structures of acid sites in Beta zeolite because of its extensive applications in acid catalysis. In this thesis, density functional calculations and Monte Carlo simulations have been performed to investigate the N-doping effects and pore structures on the adsorption of CO2 in carbonaceous materials, respectively. The 31P NMR chemical shifts of probe molecule trimethylphosphine oxide (TMPO) adsorbed on the Bransted and Lewis acids of Beta zeolite have also been computed to shed light on the distributions and structures of acid sites. These main findings are concluded as follows:(1) Density functional theory with dispersion correction (DFT-D3) has been performed to investigate the N-doping effects on the adsorption of CO2 in carbonaceous materials. The adsorption capacity increased in the following sequence for single carbon model:amide> pyridine> aniline> pyrrole. Moreover, the dispersion interaction becomes stronger as increasing the ? system. In this case pyrrole-type adsorbent shows a distinct increase in the adsorption energy. These indicate that the amide-and pyrrole-type adsorbents are the most promising CO2 trapper. In addition, from the Monte Carlo simulaiton, we acquired the CO2 adsorption isotherm at 298 K, and CO2 adsorption amount is calculated to be 3.2 mmol/g at 100 kPa, which is in accordance with the experiment. The calculation results showed that N-doping and suitable pore structures in carbon material will be beneficial for screening more efficient carbon material for CO2 capture.(2) DFT method has been carried out to study the adsorption between four types of carbon models and SO2, H2O molecules. Through the adsorption energy comparisons, we obtained the decreasing orders as following for all the carbon models:SO2> H2O> CO2, which means that the existence of SO2 and H2O will affect the adsorption of CO2 as the result of competitive adsorption.(3) Theoretical calculations were used to investigate the Bransted and Lewis acidity of Beta zeolite. Six favorable sites for Al substitution were determined by means of substitution energy.31P NMR of adsorbed TMPO has been applied to characterize different acid sites. The calculated 31P chemical shifts 5 (P)cai of TMPO adsorbed on Bransted acid site distinguish three regions as?79 ppm,70?74 ppm,?65.8 ppm, which is in agreement with the experiment data. The first type of Lewis acid site is assigned to framework Al, and the 31P chemical shift is in the range of 52?57 ppm, which has the moderate acid strength. The 31P chemical shifts of the second type of Lewis acid sites are assigned to the extra-framework Al with a wide range from 45.6 ppm (5R-A1(OH)3) to 64.0 ppm (5R-A1O+).