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The acidic gases such as SO2, NOx, H2S and CO2 are typical harmful pollutants and greenhouse gases in the atmosphere, which are also the main sources of PM2.5. The most widely used method of treating these gas molecules is to capture them with different adsorption materials, i.e., metal and nonmetallic materials such as MnO2, MoS2 and carbon-based materials. And doping transition metal atoms in adsorption materials are beneficial to the gas adsorption process. The first-principles calculation is a powerful tool for studying the adsorption properties of contaminant molecules on different materials at the molecular and atomic levels to understand surface adsorption reactions, adsorption reactivity, and structure-activity relationships which can provide theoretical guidance for laboratory researches and industrial applications. This review introduces the adsorption models and surface properties of these gas molecules on metal and nonmetallic surfaces by first-principles calculation in recent years. The purpose of this review is to provide the theoretical guidance for experimental research and industrial application, and to inspire scientists to benefit from first-principles calculation for applying similar methods in future work.

This work proposed a new strategy for the high value utilization of waste straw, in which a Mn-doped carbon/mesoporous silica composite catalyst was prepared by simultaneous utilization of carbon and silicon source from straw for low-temperature denitration. The results showed that the NO conversion rate reached 93% at 180℃ for the composite catalyst with Si/C mass ratio of 35% (Mn/ACMS (35%)). This was significantly higher than those of the activated carbon catalyst (Mn/AC) and mesoporous silica catalyst (Mn/MS), i.e., 58% and 50%, respectively. The SEM images showed that mesoporous silica nanoparticles were dispersed evenly on the carbon surface to form composite materials. XPS results indicated that Mn/ACMS (35%) catalyst showed higher content of chemically adsorbed oxygen (Oα) and Mn4+ (54.67% and 46.81%) than Mn/AC catalyst (34.38% and 17.49%) and Mn/MS catalyst (32.71% and 30.18%), which was responsible for the improved catalytic activity. Moreover, NH3-TPD results revealed that Mn/ACMS (35%) had high surface acidity of 6.47 mmol·g−1, significantly higher than Mn/AC catalyst of 1.51 mmol·g−1, which was beneficial for adsorbing NH3. H2-TPR results suggested that Mn/ACMS (35%) catalyst had much higher H2 consumption of 1.32 mmol·g−1 than Mn/AC and Mn/MS catalyst, suggesting better redox performance. The results demonstrated that the straw derived Mn-doped carbon/mesoporous silica composite catalyst can be a potential material for low-temperature denitration.

In this study, N-rich hierarchical porous carbons (NPCs) were synthesized via one step strategy from cypress sawdust with carbon nitride (CN) loading and K2CO3 activation. NPCs exhibited excellent performance for H2S removal with the sulfur capacity up to 426.2 mg/g at room temperature. It was much higher than 12.5 mg/g of porous carbon (PC) which was only activated by K2CO3. The NPCs with CN loading showed hierarchical porous structure with micropores and mesopores volume up to 0.434 and 0.597 cm3/g, respectively. Moreover, NPCs had high N contents (up to 12.37 wt%) and high relative contents of pyridinic N and pyrrolic N within 76.61–84.37%, which were identified as active sites for H2S adsorption by density functional theory calculation, enhancing H2S removal. The formation mechanism of NPCs was investigated by TG-FTIR, suggesting that CN pyrolysis result in hierarchical porous structure and rich N-containing functional groups by gradually releasing H2O, CO2 and NH3. Moreover, the NPCs showed high regeneration ability, remaining 86.6% of the initial sulfur capacity after five regeneration cycles, and sulfur (S) was the main desulfurization product (H2S + O2 → S + H2O). The results demonstrate that NPCs are promising catalysts to remove H2S efficiently with low cost and high reusability.

MnO2 has four crystal phases, whose stability and vibrational properties can affect significantly its application. In this study, a spin-polarized DFT + U method was performed to investigate the structural, mechanical, lattice dynamical, and thermodynamic properties of α-, β-, γ- and δ-MnO2. The analysis of the mechanical properties and phonon dispersion curves confirmed that all four kinds of MnO2 were mechanically and dynamically stable. The calculated mechanical properties indicated that α- and β-MnO2 were ductile, while γ-MnO2 was brittle. The phonon dispersion curves and the phonon density of states were calculated using DFPT. The phonon vibrational frequencies were analyzed in detail by the LO-TO splitting considering the non-analytical term correction. Raman and infrared active normal modes were assigned and discussed briefly to resolve the uncertainty in experiment of the assignment for the four kinds of MnO2. The symmetry of Au, Au, B3u were IR characteristic band for α-, β-, γ-MnO2, and the symmetry of Ag, A1g, Ag, A1g were Raman characteristic band for α-, β-, γ- and δ-MnO2. Finally, the thermodynamic functions of the enthalpy change and the entropy were evaluated and compared with the experimental values.

Based on the method of density functional theory, the adsorption properties of four different crystal forms of manganese dioxide α-, β-, γ- and δ-MnO2 for SO2 gas molecules have been studied in this paper. Through the analysis of adsorption energy and structural parameters, the most stable structure of SO2 adsorption on the surface of manganese dioxide were found, and the interaction mechanism between SO2 and surface reaction through state density, Bader charge transfer and charge density difference were studied. The results show that the adsorption energy decreased in the order: α-MnO2 ≈ γ-MnO2 > β-MnO2 > δ-MnO2. SO2 molecules interact with the surface of α-, β- and γ-MnO2 through relatively strong adsorption energy to form a stable adsorption structure, which is a chemical adsorption process. Meanwhile, the adsorption experiments of different crystalline manganese dioxide on SO2 gas have been studied. It can be seen that these metal oxides have good adsorption effects on SO2. Therefore, we hope that the results can provide some ideas for the preparation and research of catalytic oxidant for SO2 removal.