Chemisorption Of NH3 Research Articles

Adsorption behavior of Rh-doped graphdiyne monolayer towards various gases: A quantum mechanical analysis

In this study, the conformational properties of pure Graphdiyne (GDY) and Rh-doped (Rh-GDY) for the CO, NO, and NH3 gases are investigated using DFT computations. The doping site is optimized, and the structure parameters and electronic properties of Rh-GDY were evaluated. It is found that Rh-dosing at the optimal site (CII) increases the electrical conductivity due to decreasing of gap energy. The tendency of pure GDY toward CO, NO, and NH3 gases is low and not suitable for sensing due to physical adsorption of gases. However, Rh-GDY demonstrates exceptional performance as a gas sensor due to its strong chemisorption of CO, NO, and NH3 gases through hybridization and chemical reactions with the gas molecular orbital. As a result, Rh-GDY represents a potential gas detection sensor material with notable monitoring capabilities for gases such as CO, NO, and NH3. This research provides valuable information for advancing the creation of innovative and effective gas detection sensor technologies.

Effect of the surface termination on the adsorption of flue gas by the titanium carbide MXene

Depending on the synthesis and/or post-treatment method, MXenes become covered by surface terminations. Here, via calculations based on density functional theory, we investigate how suitable the Ti2C MXene, with nine different termination possibilities (none, Br, Cl, F, H, NH, O, OH, or S), is for adsorbing 12 flue gas molecules, namely, CH4, CO, CO2, H2, H2O, H2S, N2, NH3, NO, O2, SO2, and SO3. According to our results, a general rule is that stronger adsorption is associated to more charge transferred between the adsorbent and the adsorbate. The clean Ti2C MXene is very reactive and spontaneously dissociates nearly half the species considered. H and F surface terminations are locally replaced by O in the presence of O2 since its dissociation on Ti2CH2 or Ti2CF2 is energetically cheap and exothermic. The Ti2C(OH)2 surface is damaged by the adsorption of NO, O2, SO2, or SO3 because they bind the H atoms of hydroxyl groups and locally create O terminations. Ti2CO2 and Ti2CS2 are selective toward the chemisorption of NH3 and NO, respectively, with adsorption energies suitable for adsorption/separation applications. The Ti2CBr2, Ti2CCl2, and Ti2C(NH)2 surfaces physisorb all the investigated molecules, with binding energies that qualitatively correlate with their van der Waals volumes, thus having potential for application in reusable gas storage.

Efficient synergistic catalysis of chlorinated aromatic hydrocarbons and NOx over novel low-temperature catalysts: Nano-TiO2 modification and interaction mechanism

For efficient and synergistic elimination of chlorinated aromatic hydrocarbons (e.g., dioxins and chlorobenzenes) and NOx at low temperatures, a novel VOx–CeOx–WOx/TiO2 catalyst was systemically studied, involving the nano-TiO2 modification and the interaction mechanism between 1,2-dichlorobenzen (1,2-DCB) catalytic oxidation (DCBCO) and NH3-SCR. The VOx–CeOx–WOx/TiO2 performed excellent oxygen storage/release capacity (OSRC) and desirable 1,2-DCB conversion efficiency (95.1–97.4%) at 160–200 ℃ via M‒K and L‒H mechanism. The nano-TiO2 modification slightly impaired the 1,2-DCB oxidation to 93.6–96.2% owing to the reduced surface area and Brønsted acidity, while it distinctly enhanced NO conversion and lowered the T50 (from 162 to 112 ℃) and T90 (from 232 to 205 ℃) by improving catalyst reducibility. Based on further synergistic catalysis evaluation and in-situ DRIFT analysis, NO enhanced the 1,2-DCB conversion and complete oxidation capacity of VOx–CeOx–WOx/TiO2 by promoting active oxygen (O2−, O−, O2−) generation and improving 1,2-DCB chemosorption and subsequent oxidation. In detail, the produced HCl and H2O improved the catalyst acidity and promoted the formation of HONO and HNO3. Moreover, their generation not only facilitated the chemisorption of NH3 but also participated in the NH3-SCR via L‒H mechanism. The ensuing problem was the competitive chemisorption among 1,2-DCB, NH3, and their subsequent intermediates. As a result, NH3 had distinct advantages in competing for acid sites and active oxygen species, especially at the higher temperature, resulting in the improved NO conversion with elevated reaction temperature but the reduced 1,2-DCB conversion. The results provided essential basics for developing new catalysts to synergistically control the emission of chloroaromatic organics and NOx at low temperature.

Thulium modified MnOx/TiO2 catalyst for the low-temperature selective catalytic reduction of NO with ammonia

A new thulium (Tm) modified Mn/TiO 2 catalyst is firstly prepared to remove NO at low temperature, where the TiO 2 with relatively high specific surface area (184.3 m 2 /g) is used as carrier to support the active component MnO x , and Tm is utilized as promoter to modify the MnO x . The developed Tm–Mn/TiO 2 catalyst presents significantly improved selective catalytic reduction (SCR) de-NO x performance at low temperature with NH 3 as reducing agent. It is found that after an appropriate content of Tm is introduced, the surface concentration of Mn 4+ , the chemical adsorbed oxygen, the chemisorption of NH 3 and NO, and the reducibility of the Tm–Mn/TiO 2 catalyst are improved, which are helpful to the enhancement of NH 3 -SCR de-NO x performance. Moreover, it is discovered that, over Tm–Mn/TiO 2 catalyst, an Eley-Rideal (E-R) mechanism occurs in the reaction between adsorbed NH 3 species connected by Lewis acid sites and gaseous NO, meanwhile, a Langmuir-Hinshelwood (L-H) mechanism occurs between adsorbed NH 3 species and adsorbed NO species, where the E-R mechanism dominates the NH 3 -SCR de-NO x process. • Tm was used as a dopant to modify Mn/TiO 2 catalyst for the SCR de-NO x for the first time. • The effects of Tm on the physical and chemical properties of Mn/TiO 2 were well disclosed. • Tm 0.1 Mn/TiO 2 exhibited excellent low-temperature de-NO x performance and N 2 selectivity. • The reaction mechanisms over the Tm 0.1 Mn/TiO 2 were fully revealed by in-situ DRIFTS.

First-principle study on monolayer and bilayer SnP3 sheets as the potential sensors for NO2, NO, and NH3 detection

Layered SnP3 sheets have recently been predicted as interesting 2D material with many potential applications. In the present work, first-principles calculations were performed to investigate the possibility of layered SnP3 sheets as a candidate for detecting pollutant gases (CO, CO2, H2S, NH3, NO, and NO2). Our results indicate that CO, CO2, H2S molecules are all physisorbed on SnP3 sheets with an adsorption energy of 0.116–0.363 eV. On the other hand, the strong interactions of NH3, NO, and NO2 and SnP3 are found based on the moderate adsorption energy (around 1 eV for NO2) and large charge transfer. The monolayer SnP3 shows a higher affinity to these molecules than bilayer one. The chemisorption of NH3, NO, and NO2 molecules on layered SnP3 sheets could efficiently evoke the electrical signal, and show short recovery time for NH3, NO, and NO2 capture. The work function calculations exhibit significant responses to the NH3 and NO2 molecules. Our results proposed that SnP3 sheets could be utilized as a gas sensor for NO, NO2, and NH3, and extend the potential applications of 2D SnP3 sheets.

Insights into the highly efficient Co modified MnSm/Ti catalyst for selective catalytic reduction of NOx with NH3 at low temperature

A novel cobalt-decorated MnSm/Ti catalyst was proposed for removal of NOx at low temperatures. Catalytic performance have been tested and the physicochemical properties were comprehensively characterized using X-ray diffraction, N2 adsorption, X-ray photoelectron spectroscopy, NH3-temperature programmed desorption, H2-temperature programmed reduction and in situ diffuse reflectance infrared Fourier transform spectroscopy. The best 5CoMnSm/Ti catalyst achieved above 90% NOx conversion at 100–200 °C with a gas hourly space velocity of 60,000 h−1. The 5CoMnSm/Ti catalyst possesses increased Lewis acid sites and enhanced redox property attributed to the synergistic interaction among Mn, Co and Sm, which are beneficial to the chemisorption and activation of NO and NH3. The facile electron transfer through the redox cycle of Mn3+ + Co3+ ↔ Mn4+ + Co2+ and the enhanced oxygen mobility can maintain the surface high valence metal ions and chemisorbed oxygen at high concentration. All these factors elevate the low-temperature catalytic activity of 5CoMnSm/Ti catalyst towards selective catalytic reduction of NOx with NH3. The bidentate nitrate is a reactive nitrate species after Co doping, which can participate in the NH3-SCR. The reaction over the 5CoMnSm/Ti catalyst can proceed through both Eley–Rideal and Langmuir–Hinshelwood mechanisms, in which the Eley–Rideal mechanism is predominant owing to its fast reaction rate.

Effect of the preparation method and metal content on the synthesis of metal modified titanium oxide used for the removal of salicylic acid under UV light

ABSTRACTTitanium dioxide modified with Ag and Fe was synthesized using two preparation methods, characterized and applied to the photocatalytic degradation of salicylic acid in aqueous solution. The modified TiO2 samples were prepared by the sol–gel and wet impregnation methods starting from titanium(IV) isopropoxide and using AgNO3 and Fe(NO3)3·9H2O as precursors of the modifiers, with their content varying between 0 and 5 wt.%. Catalysts characterization was based on powder X-ray diffraction (PXRD), nitrogen physisorption at 77 K, temperature programmed reduction (H2-TPR), chemisorption of NH3 at 343 K and X-ray photoelectron spectroscopy (XPS). The photocatalytic degradation of salicylic acid by modified TiO2 was investigated under ultraviolet irradiation at 298 K considering various concentrations of the catalyst, between 100 and 1000 mgcatalyst/dm3, and of the organic molecule, between 0 and 15 mg/dm3. The catalysts most active in the degradation of salicylic acid were those having the highest Fe content.

Rapid screening of zeolite acidity by thermal response measurements using InfraSORP technology

Thermal response measurements using the recently developed InfraSORP technology are nowadays established as a versatile and rapid screening tool for the estimation of physicochemical properties of porous materials, such as adsorption capacity, surface area and porosity. In the present work, InfraSORP experiments are explored for fast screening of zeolite acidity especially for test samples available only in small quantity. Twelve MFI and beta type zeolite samples with varying molar Si/Al ratios were examined using ammonia as test gas (0.5% NH3 in nitrogen). Caused by the exothermic adsorption of ammonia on acidic sites of the zeolite samples, a characteristic temperature response curve (temperature vs. time) is observed. The specific peak area under the curve reflects the total NH3 amount adsorbed. In two consecutive adsorption/desorption runs the contributions of physisorbed and chemisorbed NH3 are distinguished. The difference between the first integral of the thermal response (caused by physisorption and chemisorption of NH3) and a second adsorption cycle (reflecting only weakly adsorbed NH3) correlates directly with the sample acidity determined by conventional temperature-programmed desorption of ammonia (TPD). Calibration of the signal versus established TPD techniques results in excellent correlation and renders the new technique as a promising high-throughput screening tool for zeolite acidity assessment in industrial process and product quality control requiring less than 30 min per sample.

Crucial support effect on the durability of Pt/MgAl2O4 for partial oxidation of methane to syngas

Catalyst durability is one of the major problems hindering the commercialization of partial oxidation of methane (POM) for syngas production. We report that a Pt/MgAl2O4-HS catalyst with the MgAl2O4-HS support being synthesized via hydrolysis solvothermal (HS) method demonstrates high stability for POM during a 500 h life testing at 900 °C without detectable coke formation, while a Pt/MgAl2O4-CP counterpart in which MgAl2O4 was prepared by an optimized co-precipitation (CP) method exhibits continuous deactivation accompanied by coking. Using a suite of characterizations incluidng BET, H2 chemisorption, XRD, STEM, TEM, TG/DTA and TPD of NH3 and CO2, we reveal that the high catalytic durability of the Pt/MgAl2O4-HS is due to the spinel surface of MgAl2O4-HS that can efficiently stabilize Pt against sintering. The Pt/MgAl2O4-CP, however, has defect Al2O3 or MgO-like species on the MgAl2O4-CP surface, inhibiting its capability to stabilize Pt. We confirm that the POM reaction undergoes a combustion-reforming pathway by monitoring the temperatures and gaseous product compositions along the catalyst bed. These results provide guidance for rational design of a longevity catalyst for POM process.

Electronic Structure Calculations of Ammonia Adsorption on Graphene and Graphene Oxide with Epoxide and Hydroxyl Groups

Ammonia adsorption on graphene (G) and graphene oxide (GO) was investigated through density functional theory calculations. In the GO system, the obtained binding energy, band gap, charge transfer and electronic structure revealed that the epoxide (GO-O) and hydroxyl groups (GO-OH) in GO enhance the NH3 adsorption, which leads to the chemisorption of NH3 on GO. The dissociation of NH3 to NH2 and formation of OH was also observed when the O and H atoms were separated at 0.985 A, 1.019 A, 1.035 A, and 1.044 A for various GO systems. The maximum charge transfer value was found to be 0.054 |e| with the binding energy of 1.143 eV for GO with a single epoxide (GO-1O) group. The charge transfer from NH3 to G or GO and the bond formation in this study agree with the reported experimental results.

Van der Waals forces and confinement in carbon nanopores: Interaction between CH4, COOH, NH3, OH, SH and single-walled carbon nanotubes

Interactions between CH4, COOH, NH3, OH, SH and armchair (n,n)(n=4,7,14) and zigzag (n,0)(n=7,12,25) single-walled carbon nanotubes (SWCNTs) have been systematically investigated within the framework of dispersion-corrected density functional theory (DFT-D2). Endohedral and exohedral molecular adsorption on SWCNT walls is energetically unfavorable or weak, despite the use of C6/r6 pairwise London-dispersion corrections. The effects of pore size and chirality on the molecule/SWCNTs interaction were also assessed. Chemisorption of COOH, NH3, OH and SH at SWCNT edge sites was examined using a H-capped (7,0) SWCNT fragment and its impact on electrophilic, nucleophilic and radical attacks was predicted by means of Fukui functions.

A nitride-based epitaxial surface layer formed by ammonia treatment of silicene-terminated ZrB2.

We present a method for the formation of an epitaxial surface layer involving B, N, and Si atoms on a ZrB2(0001) thin film on Si(111). It has the potential to be an insulating growth template for 2D semiconductors. The chemical reaction of NH3 molecules with the silicene-terminated ZrB2 surface was characterized by synchrotron-based, high-resolution core-level photoelectron spectroscopy and low-energy electron diffraction. In particular, the dissociative chemisorption of NH3 at 400 °C leads to surface nitridation, and subsequent annealing up to 830 °C results in a solid phase reaction with the ZrB2 subsurface layers. In this way, a new nitride-based epitaxial surface layer is formed with hexagonal symmetry and a single in-plane crystal orientation.

Photooxidation of Ammonia on TiO2 as a Source of NO and NO2 under Atmospheric Conditions

Ammonia is the most abundant reduced nitrogen species in the atmosphere and an important precursor in the industrial-scale production of nitric acid. A coated-wall flow tube coupled to a chemiluminescence NOx analyzer was used to study the kinetics of NH3 uptake and NOx formation from photochemistry initiated on irradiated (λ > 290 nm) TiO2 surfaces under atmospherically relevant conditions. The speciation of NH3 on TiO2 surfaces in the presence of surface-adsorbed water was determined using diffuse reflection infrared Fourier transform spectroscopy. The uptake kinetics exhibit an inverse dependence on NH3 concentration as expected for reactions proceeding via a Langmuir-Hinshelwood mechanism. The mechanism of NOx formation is shown to be humidity dependent: Water-catalyzed reactions promote NOx formation up to a relative humidity of 50%. Less NOx is formed above 50%, where increasing amounts of adsorbed water may hinder access to reactive sites, promote formation of unreactive NH4(+), and reduce oxidant levels due to higher OH radical recombination rates. A theoretical study of the reaction between the NH2 photoproduct and O2 in the presence of H2O supports the experimental conclusion that NOx formation is catalyzed by water. Calculations at the MP2 and CCSD(T) level on the bare NH2 + O2 reaction and the reaction of NH2 + O2 in small water clusters were carried out. Solvation of NH2OO and NHOOH intermediates likely facilitates isomerization via proton transfer along water wires, such that the steps leading ultimately to NO are exothermic. These results show that photooxidation of low levels of NH3 on TiO2 surfaces represents a source of atmospheric NOx, which is a precursor to ozone. The proposed mechanism may be broadly applicable to dissociative chemisorption of NH3 on other metal oxide surfaces encountered in rural and urban environments and employed in pollution control applications (selective catalytic oxidation/reduction) and during some industrial processes.

Density functional investigation of the electronic properties of B80 fullerene exposed to regioselective chemisorption of nucleophiles NH3, PH3 and AsH3

DFT calculations at B3LYP/6-31G(d,p) level are applied to investigate the effect of regioselective chemisorption of nucleophiles NH3, PH3 and AsH3 on the electronic properties of B80 fullerene based on computing CS and EFG parameters and natural charges. Three directions of approaching are considered, the frame site, endohedral and exohedral caps. Our results demonstrate CS and EFG tensors are sensitive to the positions of attached sites and that attachment of XH3 to B80 fullerene exerts not only a structural but also an electronic environment deformation to the cage. Natural charge analyses show about 0.4e transfer from NH3 ligand and about 0.8e transfer from PH3 and AsH3 ligands to the cage of B80 fullerene. Parallel to NQR parameters and natural charge analyses suggest that electronic density increases on the first neighbor of B1 in NH3–B80 models and increases on B1 and its first neighbors in PH3–B80 and AsH3–B80 models.

Comprehensive Study on the Dissociative Chemisorption of NH3 on the Sidewalls of Stone–Wales Defective Armchair (5,5) Single-Walled Carbon Nanotubes

Dissociative chemisorption of NH3 into H and NH2 on the sidewalls of (5,5) armchair Stone–Wales defective single-walled carbon nanotubes (SWCNTs) has been investigated using B3LYP/6-31G(d) and M06-2X/6-31G(d) levels of theory. In particular, H• and NH2• have been attached to the adjacent carbon atom sites on and around the Stone–Wales defect (SWD). Here, we consider SWD with two different orientations in finite H-terminated (5,5) SWCNTs. The reaction energy data suggest that the dissociative chemisorption of NH3 on the surface of the Stone–Wales defective SWCNTs is mostly endothermic except the adsorption at very few defect sites, wherein the chemisorption process is exothermic at the M06-2X/6-31G(d) level. Our systematic study reveals that the SWD generated by 90° rotation of nearly axial C–C bond in (5,5) SWCNT is more favorable for the chemisorption of ammonia than the nanotube containing SWD with another orientation. The HOMO–LUMO energy gap values of defect-free and Stone–Wales defective SWCNTs are s...

Chemisorption of NH3 at the open ends of boron nitride nanotubes: a DFT study

Considering the thermodynamic aspects and reaction pathways of chemical adsorption of NH3 molecule at the open ends of boron nitride nanotubes (BNNTs), theoretically, it was found that the open-ended BNNTs are able to cleave the N–H bond of NH3 via a one- or two-stepwise mechanism. The N-enriched and B-enriched open-ended BNNTs show a nucleophilic and electrophilic behavior toward the NH3, respectively. Besides, some effects of this chemical adsorption on the electronic properties of BNNTs were explored.

Accessibility and Dispersion of Vanadyl Sites of Vanadium Silicate-1 Nanoparticles Deposited in SBA-15

Vanadium silicalite-1 (VS-1) nanoparticles dispersed onto the mesoporous walls of SBA-15 silica have characteristics different from those of the full-grown VS-1. In particular, the vanadium-binding site differs extensively. Here, we monitor the local environment of VO2+ with different electron paramagnetic resonance (EPR) techniques to obtain information about the heterogeneity of the vanadyl sites, the effect of a calcination/reduction cycle, and the subsequent adsorption of 13CO2 and NH3 to the vanadyl sites for both full-grown VS-1 and VS1-SBA15. Furthermore, two-cycle CO2 and NH3 adsorption experiments were performed. While the latter showed no chemisorption of CO2 at 373 K for both materials, clear evidence was found for ligation of CO2 to vanadyl in full-grown VS-1 by the detection of a strong 13C hyperfine value. This strong binding was not detected for the vanadyl centers in VS1-SBA15. Chemisorption of NH3 was detected for all samples both by two-cycle adsorption experiments and by EPR.

Theoretical Prediction of the N−H and O−H Bonds Cleavage Catalyzed by the Single-Walled Silicon Carbide Nanotube

Effective cleavage of the N−H and O−H bonds at “metal-free” centers has attracted considerable attention due to the fundamental and industrial importance. In this paper, we show by density functional theory calculations that the pure silicon carbide nanotube (SiCNT) can effectively cleave the N−H bond of ammonia and the O−H bond of H−OX (X = H, CH3, and C2H5). Both the N−H and O−H bond cleavage undergoes two evolution steps: (i) molecular chemisorption of NH3 or H−OX followed by (ii) the activated N−H bond of NH3 or O−H cleavage of H−OX. For the N−H bond cleavage of ammonia, the adsorption energy (−1.199 eV) and the subsequent H-transfer barrier (0.842 eV) from the Si atom to the neighboring C atom indicate a zero total N−H splitting barrier by the Si+−C− center of SiCNT. Similarly, the SiCNT can also split the O−H bonds of H−OX with a considerably larger exothermicity (ca. −1.800 eV) than that of the N−H bond cleavage (−1.370 eV). Subsequently, the resulting NH2 or OX groups and H atom can be converted t...

Fe(III)-montmorillonite: Basic properties and diffusion of tracers relevant to alteration of bentonite in deep geological disposal

In the deep geological repository of high-level nuclear waste (HLW), the interaction of carbon steel (Fe) overpack container and the back-fill clay mineral, montmorillonite (mont), is an important issue to be clarified in view of the long-term performance of clay mineral as an engineered barrier. To arrive at some understanding of the altered clay at the Fe/clay interface, Fe(III)-mont is used here for preliminary investigation to see if there is any considerable difference in the basic properties, mainly diffusion of tracers with respect to Na-mont, although Fe(III)-mont is not a realistic analogue of altered clay in the reducing chemistry conditions anticipated in the subsurface of HLW, unlike Fe(II)-mont which is difficult to prepare and handle in the ambient atmosphere due to its gradual oxidation. Fe(III)-mont was prepared by the conventional cation exchange method with 0.4 M FeCl 3 solution. The total Fe(III) ions adsorbed was about 1.42 meq/g, while the CEC of parent clay was 1.2 meq/g. Thus ∼ 18% excess Fe(III) ions were present presumably as iron oxy hydroxide, i.e., about 2 wt.% with respect to FeOOH or Fe(OH) 3 in the bulk sample. The sample was further characterized by X-ray diffraction (XRD), infrared (IR), thermogravimetry, magnetization, and the methylene blue (MB) adsorption. From these conventional techniques, the minor Fe-oxide phase associated with the Fe(III)-mont could not be detected, although we cannot rule out its existence. The paramagnetic behavior of Fe(III)-mont was evident from the Curie–Weiss plot (300 K down to 5 K). Some basic properties like osmotic swelling, diffusion of tracers and thermal stability are evaluated here. The osmotic swelling of Fe(III)-mont was very low, ∼ 5 ml/g, while that of Na-mont was > 40 ml/g. Apparent diffusion coefficient ( D a) of tracers viz., 22Na +, HTO and 36Cl − was determined using compacted (dry density, ρ d = 1.0, 1.6 Mg m − 3 ), water-saturated Fe(III)-mont. There was no considerable change in D a of these tracers in Fe(III)-mont when compared to that in Na-mont, in spite of higher pore water availability in Fe(III)-mont due to reduced swelling. For instance at ρ d = 1.6 and 25 °C, D a (×10 − 11 m 2/s) of 22Na + (2.6) was same as that in Na-mont whereas D a of HTO (11.4) and 36Cl − (1.0) have varied marginally. For comparison, the corresponding D a (×10 − 11 m 2/s) values in Na-mont were 2.7, 7.2 and 3.4, respectively. Also, at ρ d = 1.6, the diffusion activation energy ( E A, kJ mol − 1 ) of HTO (17.5) in Fe(III)-mont was comparable to that in free water, however, E A of 36Cl − (13.1) was remarkably low, which may be ascribed to the so-called ‘anion exclusion’ effect. Furthermore, thermal stability of Fe(III)-mont indicated the existence of interlayer Fe(III) in the ionic state up to ∼ 190 °C, based on the XRD and MB adsorption test. On heating to > 200 °C, irreversible dehydration of interlayer cations occurred, and the chemisorption of NH 3 indicated two distinct acid sites at about 300 °C and 600 °C.

Dissociation Chemistry of Gas Molecules on Carbon Nanotubes—Applications to Chemical Sensing

It is well known in the literature that carbon nanotubes (CNTs) interact weakly with many gas molecules like H2O, O2, CO, NH3, H2 and NO2, to name a few. Exposure to NO2, O2 and NH3 significantly affects the electrical conductance of a single wall nanotube (SWNT). These can be explained using a simple charge transfer picture, which results in the observed changes in the hole conduction of the tubes. It is also known that pure SWNTs only weakly interact with these molecules. We have recently investigated (Andzelm , 2006) how common defects in CNTs [Stone-Wales (SW), monovacancy, and interstitial] influence the chemisorption of NH3. This paper is a continuation of our previous work. Here, we further investigate, via density functional theory (DFT) calculations, the effects of SW defects on the adsorption/dissociation of and O2 and H2O. We also study the diffusion of adsorbed oxygen atoms on the nanotube surface in the vicinity of the SW defect, as well as the dissociation of in the presence of adsorbed oxygen atoms.