Adsorption of NOx with NH3 on γ-Al2O3 and Its Effects on the Adsorption of As2O3 Based on DFT

CO2 adsorption enhancement over Al/C-doped h-BN: A DFT study

Reducing energy barriers of CO₂ being chemisorbed on hexagonal boron nitride (h-BN) is a kernel step to efficiently and massively capture CO₂. In this study, aluminum/carbon (Al/C) atoms are used as dopants to alter surface potential fields of h-BN, which aims at lowering energy barriers of adsorption processes. Through theoretical calculations, direct-adsorption structures/properties of CO₂, joint-adsorption structures/properties of CO₂/H₂O, transition state (TS) energy barriers, effects of temperatures on adsorption energies/TS energy barriers and changes of reaction rate constants over different adsorbents are investigated in detail in order to reveal how doping of Al/C atoms promotes CO₂ adsorption strength over doped h-BN. According to DFT calculation results, the average adsorption energy of CO₂ being directly adsorbed on Al/C-doped h-BN arrives at -59.43 kJ/mol, which is about 5 times as big as that over pure h-BN. As to the average adsorption energy of CO₂/H₂O and relevant TS energy barrier, they are modified to -118.89 kJ/mol and 40.23 kJ/mol over Al/C-doped h-BN in contrast with -33.91 kJ/mol and 1695.11 kJ/mol over pure h-BN, respectively. What is more, based on thermodynamic analyses and reaction dynamics, the average desorption temperatures of CO₂(/H₂O) are promoted over doped h-BN and the temperature power exponent is negatively correlated with the activation energy in the Arrhenius equation form. The complete understanding of this study would supply crucial information for applying Al/C-doped h-BN to effectively capturing CO₂ in real industries.

Arsenic adsorption enhancement performances of Mn-modified γ-Al2O3 with flue gas constituents involved

Some flue gas constituents have negative effects on As₂O₃ adsorption of γ-Al₂O₃ so promoting arsenic adsorption performances under complicated flue gas conditions is necessary based on previous studies. In this study, γ-Al₂O₃ is modified with manganous nitrate and then Mn-modified γ-Al₂O₃ is used as the adsorbents in experiments. Besides, molecular dynamics (MD) simulations and density functional theory (DFT) calculations are performed to explore mechanisms of how loadings of Mn enhance arsenic adsorption features of γ-Al₂O₃ when being affected by flue gas constituents in microscale and mesoscale, respectively. As for DFT calculations, it is uncovered that electron transfer/interaction among As₂O₃, flue gas constituents and Mn-modified γ-Al₂O₃ mostly influences arsenic adsorption. For MD simulations, it is expounded that the collision and aggregation of As₂O₃ and flue gas constituent molecules have most impact on arsenic adsorption. As far as experiments are concerned, they are conducted to show the macroscopic characterizations of arsenic adsorption performances, corresponding to results of DFT calculations and MD simulations. The understanding of these three different aspects could supply significant references for utilization of Mn-modified γ-Al₂O₃ in real industries to remove arsenic under complex flue gas conditions.

Fe-Catalyzed CO2 Adsorption over Hexagonal Boron Nitride with the Presence of H2O

The energy barrier of CO₂ chemically adsorbed on hexagonal boron nitride (h-BN) is relatively big. In order to cut down the energy barriers and facilitate fast adsorption of CO₂, it is necessary to apply catalysts as a promoter. In this study, single-atom iron is introduced as the catalyst to reduce the energy barriers of CO₂ adsorbed on pure/doped h-BN. Through density functional theory calculations, catalytic reaction mechanisms, stability of single-atom iron fixed on adsorbents, CO₂ adsorption characteristics, and features of thermodynamics/reaction dynamics during adsorption processes are fully investigated to explain the catalytic effects of single-atom iron on CO₂ chemisorption. According to calculations, when CO₂ and OH^- get into activated states (i.e., CO₂^•- and ^•OH) with the help of single-atom iron, their chemical activities will be promoted to a large degree, which makes the transition state (TS) energy barrier of HCO₃^- to decrease by 92.54%. In the meantime, it is proved that single-atom iron could be stably fixed on doped h-BN with the binding energy larger than 2 eV to achieve sustainable catalysis. With the presence of single-atom iron, TS energy barriers of CO₂ adsorbed on h-BN with the presence of H₂O decreased by 94.39, 78.87, and 30.63% over pure h-BN, 3C-doped h-BN, and 3N-doped h-BN, respectively. In the meantime, thermodynamic analyses indicate that TS energy barriers are mainly determined by element doping and temperatures are a little beneficial to the reduction of TS energy barriers. With the above aspects combined, the results of this study could supply crucial information for massively and quickly capturing CO₂ in real industries.