Adsorption Behaviors Of NH3 Research Articles

Testing and Evaluation Performance of Borosilicate Glasses for Ammonia, Nitrate, and Total Nitrogen Removal from Industrial Wastewater

Several studies were conducted utilizing various adsorbents in an effort to remove NH3+, NO3, and total nitrogen (TN) by adsorption process. In this study, Borosilicate glass is used as an adsorbent material. The effectiveness of the adsorbent in removing NH3+, NO3, and TN was examined, that in relation to the effect of solution characteristics. Three different types of glass intermediate oxides (Al2O3, SnO, and Bi2O3) were used to synthesize three different samples of borosilicate glass (adsorbents), that to study their effect on the adsorption efficiency of borosilicate glass. Aluminum oxide Al2O3 was used to synthesize adsorbent (I), tin oxide SnO was used to synthesize adsorbent (J), and bismuth oxide Bi2O3 was used to synthesize adsorbent (K). Adsorbents (I, J, and K) achieved a clear improvement in the performance of the adsorption process. Despite the convergence of competencies, adsorbents J and K were superior to adsorbent I. With adsorbent K and an initial concentration of contaminants 28 mg NH3+/ L, 28 mg NO3/ L, and 60 mg TN / L, the removal efficiency of NH3+, NO3, and TN was 49.5%, 55%, and 40%, respectively. The removal efficiency increased with initial concentration of contaminants increasing, which became around 79% NH3+, 93% NO3, and 88% TN for adsorbent K. The best efficiency of ammonia removal achieved with pH value 8.9, it was 64.1%, 75.3%, and 77.1% for adsorbents I, J, and K, respectively. The highest efficiency of nitrate removal was in acidic case, reaching 90.1%, 95.2%, and 93.8% for adsorbents I, J, and K, respectively, at pH value 4.1. Adsorption data were fitted with Langmuir and Freundlich isotherm models to demonstrate the adsorption behavior of NH3+, NO3, and TN onto adsorbents (I, J, and K). It was found that the data were well fitted to both models. Overall, the findings demonstrated that borosilicate glass has the potential to be an effective adsorbent for the removal of ammonia, nitrate, and total nitrogen from industrial effluent.

Zr3C2O2 MXene as promising candidate for NH3 sensor with high sensitivity and selectivity at room temperature

MXene materials have attracted extensive attention due to their graphene-like structures and promising future applications in many fields. The gas adsorption behavior of NH3, NO, H2S, N2, H2, O2 and CO on Zr3C2O2 are investigated by using first principles simulations. The calculated adsorption energies and charge transfers indicate that Zr3C2O2 could be a promising candidate as room-temperature NH3 gas sensing material due to its high selectivity, superb sensitivity and short recovery time. The factors influencing the gas sensing behavior of MXenes are analyzed. The results show that the gas sensing performance of MXenes can be modulated by altering the interaction between the gas molecules and the substrate through the surface functional group, transition metal, and the biaxial strains. This study could guide the feasibility of using monolayer Zr3C2O2 as NH3 gas sensor in further experimental applications and provide an effective way to tailor MXene series in compliance with various applications.

The effect of the active carbonyl groups and residual acid on the ammonia adsorption over the acid-modified activated carbon

The deep insight into the adsorption mechanism of ammonia (NH3) over acid-modified activated carbon will be of great significance to develop more efficient carbon materials for NH3 adsorption. In this work, a co-adsorption mechanism of NH3 and residual nitric acid (HNO3) on the active carboxyl site is proposed to elaborate the enhanced NH3 adsorption capacity over the acid-modified activated carbon based on both the experimental and density functional theory (DFT) results. The adsorption behaviors of NH3 over the different acid-modified activated carbon samples show that the activated carbon modified by 10 M HNO3 at 90 ºC possesses the best NH3 adsorption capacity (40 mg/g), and the residual HNO3 can be observed with the release of both NOx and NH3 during the heat treatment of the used HNO3-modified activated carbon. The multiple structural characterizations reveal that the activated carbon can be oxidized and etched by HNO3 with enriched pore structure and oxygen-containing functional groups, and acidic functional groups play a key role in the improved NH3 adsorption capacity. DFT calculations further display that the carboxyl functional group can strongly interplay with NH3 or HNO3 with the lowest adsorption energy (-0.66 eV and -0.79 eV, respectively), and the co-adsorption of NH3 and HNO3 around the carboxyl functional group forms a strong circular hydrogen-bond network among NO3−, NH4+ and carbonyl and further decreases the adsorption energy (-1.63 eV). The experimental and theoretical results together demonstrate that the oxidation and etching of activated carbon by acid enrich the active surface carboxyl functional groups, and the co-adsorption of NH3 with the residual HNO3 around the carboxyl functional group through the strong circular hydrogen-bond network accounts for the enhanced NH3 adsorption capacity of the acid-modified activated carbon.

A DFT study on adsorption behaviors of NH3 and SO2 on MnCe/TiNTs catalyst

Manganese-cerium catalyst has attracted much attention due to its extraordinarily good low-temperature performance for detrinification technology, but its poor SO2 resistance limits its wide application. A suitable catalyst carrier can enhance the low-temperature activity and anti-poisoning performance of catalyst. In this paper, density functional theory (DFT) was used to construct MnCe catalyst models that supported by conventional TiO2 and TiO2 nanotubes (TiNTs) (denoted as MnCe/TiO2 and MnCe/TiNTs, respectively) to simulate adsorption behaviors of NH3 and SO2 molecules on catalyst surface. The adsorption energies (Eads) of NH3 and SO2 on catalyst surface, projected density of states (PDOS) of surface metal/nonmetal atoms and Mulliken charge were calculated. The results show that NH3 and SO2 molecules prefer to adsorb on top sites of Mn and Ce atoms respectively, but the competitive adsorption between NH3 and SO2 for top site of Ce atom on MnCe/TiO2 surface exists, for their Eads values (-0.42 eV and -0.44 eV) are similar. TiNTs alleviates their competitive adsorption by increasing the adsorption capacity of NH3 and weakening that of SO2 on catalyst surface. It attributes to the fact that TiNTs increases the coordination unsaturation of Mn and Ce atoms that enhances the electron transformation from NH3 molecule to Mn atom and weakens the electron-donating ability of Ce atom to SO2 molecule. In addition, TiNTs own abundant hydroxyl groups (OH) which can act as surface Brønsted acid sites for NH3 adsorption. These facts deeply reveal the promotion mechanism of TiNTs for low-temperature denitrification activity and sulfur poisoning resistance of MnOx-CeO2 catalyst from a microscopic perspective.

Adsorption of NH3 and NO2 Molecules on Sn-Doped and Undoped ZnO (101) Surfaces Using Density Functional Theory

The adsorption and interaction mechanisms of gaseous molecules on ZnO surfaces have received considerable attention because of their technological applications in gas sensing. The adsorption behavior of NH3 and NO2 molecules on undoped and Sn-doped ZnO (101) surfaces was investigated using density functional theory. The current findings revealed that both molecules adsorb via chemisorption rather than physisorption, with all the adsorption energy values found to be negative. The calculated adsorption energy revealed that the adsorption of the NH3 molecule on the bare ZnO surface is more energetically favorable than the adsorption of the NO2 molecule. However, a stable adsorption configuration was discovered for the NO2 molecule on the surface of the Sn-doped ZnO surface. Furthermore, the adsorption on the undoped surface increased the work function, while the adsorption on the doped surface decreased. The charge density redistribution showed charge accumulation and depletion on both adsorbent and adsorbate. In addition, the density of states and band structures were studied to investigate the electronic behavior of NH3 and NO2 molecules adsorbed on undoped and Sn-doped ZnO (101) surfaces.

Study on the mechanism of NOx reduction by NH3-SCR over Mn and M(M=V,Ti) co-doped CoCr2O4 catalyst

Being based on the first-principles calculation method of density functional theory, our work calculated the optimized configuration of CoCr2O4(100) before and after co-doping of Mn and V(Ti). The adsorption behaviors of NH3, NO, NO2 and other gas molecules on the catalyst before and after doping were simulated. The optimized structures and related energy distribution of NH3 dehydrogenation reaction and SCR reaction on Mn0.1Co0.9V0.1Cr1.9O4 and Mn0.1Co0.9Ti0.1Cr1.9O4 catalysts were also fully studied. Our results reveal that the co-doping of heteroatom towards CoCr2O4(100) may result in electron migration and lattice dislocations as well as improving the surface acid activity. Therefore, the co-doping of Mn and V or Mn and Ti are believed to improve the adsorption of NH3, NO, NO2 and other gas molecules on the CoCr2O4 catalyst and significantly reduce the activation energy barrier of the NH3 dehydrogenation reaction and the SCR reaction. Furthermore, we studied the adsorption of SO2 and H2O on the co-doped catalyst, which exhibited that the co-doping of Mn and Ti may effectively improve the water and sulfur resistance of the catalyst. Our research are expected to be full of important theoretical guiding significance for the development, preparation and modification of cobalt-chromium spinel catalysts.

Adsorption behaviors of NH3 and HCl molecules on Fe-based crystal planes: A DFT study

By adopting the First-principles method based on the density functional theory (DFT), the adsorption properties of NH3 and HCl molecules intermingled in crude oil on the Fe-based crystal planes exposed on the inner surface of a duct in a crude distillation column have been conducted. Specifically, the calculated adsorption energy of NH3 and HCl reveal the most stable adsorption sites on the three planes, and the free energy at different temperatures was corrected. Furthermore, the charge density difference and the Bader charge obviously illustrate the direction of charge transfer and the valence of the atoms after adsorption. The results of projected electron density of states (PDOS), electron localization function (ELF) and the crystal orbital Hamilton population (COHP) reveal the nature of chemical bonds and the influence of specific atomic orbitals. Accordingly, the adsorption type of the two molecules on the Fe-based crystal planes is chemical adsorption. Considering the nature of the chemical bond and the multi-component environment of the distillation column, we infer that the possible causes of corrosion are coordination ions, hydrogen embrittlement and Cl− concentration.

Understanding the adsorption behavior of small molecule in MoS2 device based on first-principles calculations

Although layered MoS2 has been proposed as a potential candidate for gas detection devices due to high surface-to-volume ratio, high sensitivity, and selectivity, the adsorption behavior of small molecules is still ambiguous. Here, we performed the first-principles calculations to investigate the adsorption behavior of small molecules on layered MoS2 surface, and the effects of defects and environment are considered. Our results reveal that NO and NO2 can be chemically adsorbed on defective monolayer MoS2, which is attributed to the forming of covalent bonds. And the forming of covalent bonds can lead to an increase in adsorption energies. Whereas, gas molecules can only be physically adsorbed on perfect MoS2. Meanwhile, as compared with adsorption behavior of NH3, NO, and NO2 on clean MoS2, the environmental gases (CO2, N2, and H2O) may result in an increase in adsorption strength of NH3, NO, and NO2 on MoS2 surface.

Coverage-dependent adsorption of small gas molecules on black phosphorene: a DFT study

Using Density Functional Theory (DFT), we perform a detailed computational study to explore the adsorption behaviors of NH3, NO, NO2, CO and CO2 gas molecules on a black phosphorene surface at several coverages. Van der Waals (vdW) interactions were taken into account within the optB88-vdW functional. In addition, a comparison with the strongly-constrained and appropriately-normed (SCAN) meta-generalized gradient approximation (meta-GGA) is discussed. Our calculations show that all molecules adsorb on the surface of black phosphorene with different favorable adsorption sites, depending on the molecule's geometry and orientation. Alongside the adsorption energies, other properties are presented including the adsorption distances and charge transfers. At high coverages, the adsorption energies per molecule show that the functionals start to behave differently as the coverage rate increases. The significant charge transfer between NO and NO2 molecules and black phosphorene suggests its potential integration towards efficient nitrogen-oxide detectors.

Quantum chemistry study of SCR-NH3 nitric oxide reduction on Ce-doped γFe2O3 catalyst surface

The doping of Ce on γ-Fe2O3 catalyst surface can improve the NO removal catalytic activity and widen the temperature window of activity. However, the mechanism of promoting the De-NOx activity of γ-Fe2O3 catalyst by Ce doping has not been revealed. In this paper, therefore, the doping of Ce on γ-Fe2O3(001) surface and the adsorption behavior of NH3 and NO as well as the reaction pathway were studied by the density functional theory (DFT). The results show that the doping of Ce on γ-Fe2O3(001) surface can lead to the migration of electrons on the surface of catalyst and cause the dislocation of the surface lattice, so as to improve the surface acid activity. Thus, the Ce doping can increase the adsorbed energy of the modified γ-Fe2O3 catalyst to NO and NH3 and decrease the activation energy barrier of the rate determining step in SCR reaction. Furthermore, the effects of Ce doping will change with the concentration of the Ce doping, and the excellent SCR De-NOx efficiency will be obtained in the optimal doping amount. On the other hand, O2 makes an important effect. Which makes the activation energy barrier of the rate determining step under aerobic condition lower than that under anaerobic conditions, causes the surface active O to react with NO to form NO2 and perform a rapid SCR reaction. The Ce doping can promote the dissociation of O2 on the active cation site and reduce the activation energy barriers of above steps. Accordingly, the doping of Ce on γ-Fe2O3 catalyst surface can improve the SCR process.

A Comprehensive Study on the Reductive Amination of 5‐Hydroxymethylfurfural into 2,5‐Bisaminomethylfuran over Raney Ni Through DFT Calculations

AbstractReductive amination of furfuryl alcohol, furfural and 5‐hydroxymethylfurfural (5‐HMF) were carried out on various metal catalysts. Over Raney Ni catalyst, we obtained the highest furfurylamine yields of 81.8 % and 94.0 % from furfuryl alcohol in absence and presence of H2, respectively. While furfural was used as the substrate, 100 % yield of furfurylamine could be achieved over Raney Ni under rather moderate conditions. Although 5‐HMF was completely converted over all catalysts used, the highest yield of 2,5‐bisaminomethylfuran (60.7 %) was obtained over Raney Ni at 160 °C in 12 h. The DFT calculations on the adsorption behavior of NH3 and H2 on different metal surfaces showed that the difference of the adsorption energy between NH3 and H2 on Ni is lower than those of other metals, indicating that less metal active sites on Ni surface is occupied by NH3, which leaves more active sites for dehydrogenation/hydrogenation reactions and in the end promotes the reductive amination reactions.

Adsorption behavior of NH3 and NO2 molecules on stanene and stanane nanosheets – A density functional theory study

Using density functional theory method, we investigate the adsorption properties of NH3 and NO2 molecules on stanene and stanane nanosheets. The adsorption of molecules is explored based on the charge transfer, energetics, energy band gap and average energy gap variation. Moreover, the optimal adsorption sites of NH3 and NO2 molecules are identified on stanene and stanane nanosheets. Besides, the state-of-the-art provides the key features for the development of chemi-resistive nanosensor based on stanene and stanane nanosheets upon adsorption of NH3 and NO2 molecules. Furthermore, the study shows that adsorption of NO2 molecules is more prominent rather than NH3 molecules.

Different Poisoning Effects of K and Mg on the Mn/TiO2 Catalyst for Selective Catalytic Reduction of NOx with NH3: A Mechanistic Study

It is well recognized that both alkali and alkali earth metals have a poisoning effect on selective catalytic reduction (SCR) catalyst. In this study, the different poisoning effects of K and Mg on Mn/TiO2 catalyst were investigated. It was found that the deactivation effect of K was much stronger than that of Mg. The effect of K or Mg addition on the physicochemical properties of Mn/TiO2 catalyst was investigated based on N2 adsorption, XRD, XPS, H2-TPR, NH3-TPD, and NO-TPD techniques. The results indicated that the addition of K or Mg on Mn/TiO2 catalyst would decrease its specific area, promote the crystallization of TiO2, and lead to a decrease of Mn4+ and surface chemisorbed oxygen. Furthermore, the presence of K or Mg on Mn/TiO2 catalyst would lead to the drop of reducibility and the adsorption capacity of NH3 and NOx species. In addition, the adsorption behavior of NH3 and NOx and their surface reactions over the fresh and poisoned Mn/TiO2 catalysts were investigated by in situ DRIFT study. It was ...

Cation synergies affect ammonia adsorption over VOX and (V,W)OX dispersed on α-Al2O3 (0001) and α-Fe2O3 (0001)

The catalytic behavior of oxide-supported metal oxide species depends on the nature of the support and the presence of co-catalysts. We use density functional theory (DFT) to explore the relationship between the structure and chemical behavior of vanadium oxide in light of its industrial use for the selective catalytic reduction of nitric oxide with ammonia (NO-SCR). The relative stabilities of dispersed VOX monomers, dimers, and long-chain oligomers on two model oxide support surfaces with similar structure but drastically different chemical behavior, α-Al2O3 (0001) and α-Fe2O3 (0001), are determined. The effect of added tungsten, known to promote NO-SCR, is also investigated on the relatively inert α-Al2O3 (0001) support. We find that the adsorption behavior of NH3, representing the first step of the NO-SCR reaction, depends strongly on the VOX local structure. Protonation of NH3 to NH4+ over surface hydroxyls is energetically favorable over VOX-WOX dimers and VOX oligomers, which are stabilized by the reducible α-Fe2O3 (0001) support.

Adsorption of NO and NH3 over CuO/γ-Al2O3 catalyst

The selective catalytic reduction reaction belongs to the gas-solid multiphase reaction, and the adsorption of NH3 and NO on CuO/γ-Al2O3 catalysts plays an important role in the reaction. Performance of the CuO/γ-Al2O3 catalysts was explored in a fixed bed adsorption system. The catalysts maintain nearly 100% NO conversion efficiency at 350 °C. Comprehensive tests were carried out to study the adsorption behavior of NH3 and NO over the catalysts. The desorption experiments prove that NH3 and NO are adsorbed on CuO/γ-Al2O3 catalysts. The adsorption behaviors of NH3 and NO were also studied with the in-situ diffusion reflectance infrared Fourier transform spectroscopy methods. The results show that NH3 could be strongly adsorbed on the catalysts, resulting in coordinated NH3 and NH 4 + NO adsorption leads to the formation of bridging bidentate nitrate, chelating bidentate nitrate, and chelating nitro. The interaction of NH3 and NO molecules with the Cu2+ present on the CuAl2O4 (100) surface was investigated by using a periodic density functional theory. The results show that the adsorption of all the molecules on the Cu2+ site is energetically favorable, whereas NO bound is stronger than that of NH3 with the adsorption site, and key information about the structural and energetic properties was also addressed.

Adsorption and electron stimulated desorption of NH3/TiO2(110)

Adsorption and electron stimulated processes of NH3 on rutile TiO2(110) have been studied by means of x-ray photoemission spectroscopy (XPS) and low-energy ion scattering (LEIS). Defects, mostly surface oxygen vacancies, can be produced easily on TiO2 surfaces by thermal treatment or by rare gas ion sputtering. We have used three differently prepared TiO2 surfaces to study the influence of the substrate defect structure on the interaction with NH3: a stoichiometric surface, a thermally treated (slightly oxygen deficient), and a sputtered (highly oxygen-deficient) surface. The adsorption behavior of NH3 on all these surfaces is quite similar. NH3 adsorbs molecularly, with a saturation coverage of ∼0.16–0.19 monolayers, the latter for a highly oxygen-deficient surface. The electron stimulated desorption (ESD) behavior is quite different: In the limit of a stoichiometric surface, electron irradiation induces the desorption of NH3 molecules, with a desorption cross section of ∼ 1 × 10−16 cm2. When the highly oxygen-deficient TiO2 surface is used as substrate, besides desorption, electron stimulated dissociation of NH3 takes place, with atomic nitrogen being the final product of the dissociation process. This atomic nitrogen is adsorbed in subsurface sites, as confirmed by angle-resolved XPS. Under certain conditions, an electron stimulated formation of surface nitride is observed. These measurements provide direct evidence for the role of surface defects in electron stimulated reaction pathways.