Coadsorption Of Gases Research Articles

Low-Concentration NOx Gas Analysis Using Single Bimodular ZnO Nanorod Sensor.

Quantitative measurement of the nitrogen oxide mixture (NOx, usually of NO and NO2) usually relies on sophisticated, space-consuming, and expensive spectroscopy techniques such as gas chromatography (GC), Fourier-transform infrared spectroscopy (FTIR), and chemi-luminescence detection (CLD). The direct and portable measurement solutions are lacking in this regard. In this work, by utilizing the bimodular sensing strategy, we successfully demonstrated the differential measurement of NOx with errors smaller than 8.3%, by correlating the sensor electrical and electrochemical responses. The effective detection is successfully displayed in the low-concentration ranges of 1-10 ppm for NO and 100 ppb-1 ppm for NO2, where weak competitive gas co-adsorption mitigated the cross-sensitivities compared to the higher-concentration range. Based on the electron occupation with negligible competitive adsorption, the accurate theoretic prediction of the mixture responses versus component concentration relieves the reliance on repeated calibration and empirical functions. With the miniaturized size and simplified electrical feedthrough, the single bimodular nanorod sensor provides a promising solution for direct and portable NOx analysis at low concentrations.

Molecular Sieving of Acetylene from Ethylene in a Rigid Ultra-microporous Metal Organic Framework.

Rigid molecular sieving materials are the ideal candidates for gas separation (e. g., C2 H2 /C2 H4 ) due to their ultrahigh adsorption selectivity and the absence of gas co-adsorption. However, the absolute molecular sieving effect for C2 H2 /C2 H4 separation has rarely been realized because of their similar physicochemical properties. Herein, we demonstrate the absolute molecular sieving of C2 H2 from C2 H4 by a rigid ultra-microporous metal-organic framework (F-PYMO-Cu) with 1D regular channels (pore size of ca. 3.4 Å). F-PYMO-Cu exhibited moderate acetylene uptake (35.5 cm3 /cm3 ), but very low ethylene uptake (0.55 cm3 /cm3 ) at 298 K and 1 bar, yielding the second highest C2 H2 /C2 H4 uptake ratio of 63.6 up to now. One-step C2 H4 production from a binary mixture of C2 H2 /C2 H4 and a ternary mixture of C2 H2 /CO2 /C2 H4 at 298 K was achieved and verified by dynamic breakthrough experiments. Coupled with excellent thermal and water stability, F-PYMO-Cu could be a promising candidate for industrial C2 separation tasks.

Trace Adsorption of Light Hydrocarbons at Low Temperatures: Influence of Carrier Gas Coadsorption

During the adsorptive separation of light hydrocarbons in the trace range, significant coadsorption of the carrier gas may occur due to low temperatures and much higher concentrations of the carrier gas compared to the adsorptive. This results in a reduction of the adsorbent’s capacity, which leads to problems in industrial adsorber design and an incorrect interpretation of adsorption mechanisms. So far, there are only few studies on the carrier gas influence, and no data exist for low temperatures. In this work, we present experimental adsorption isotherms of methane and ethane from nitrogen and helium at temperatures between −80 and +20 °C on activated carbon and zeolite 13X. A comparison of the adsorption isotherms and the isosteric adsorption enthalpy reveals that coadsorption increases strongly with low temperatures, low partial pressures, and weak interactions between adsorptive and adsorbent. Finally, coadsorption is shown to be stronger on activated carbon than on zeolite 13X.

Effects of N and S Functionalities on Binary Gas Co-adsorption on a Coal Macromolecule

Effects of N and S functionalities on co-adsorption of CH4 + N2 and CH4 + CO2 on the coal vitrinite macromolecule model (CVMM) were explored using molecule simulation. Inclusion of the sulfoxide, amine, and sulfide functionalities can enhance SCO2/CH4 (selectivity of CO2 over CH4), while the pyrrole and pyridine functionalities could not. The higher mole fraction of CO2 could reduce the pressure required to reach the stable equilibrium state as well as SCO2/CH4. Microporous calculation results suggest that the microporous size distribution (MSD) of amine–CVMM (median pore size, DM, 8.24 A; free volume probed by He, VdF, 7105.55 A3/cell) and sulfoxide–CVMM (DM, 7.92 A; VdF, 7812.96 A3/cell) are most suitable for CH4 adsorption, followed by pyrrole–CVMM (DM, 7.18 A; VdF, 6812.96 A3/cell). The inclusion of N and S functionalities can distinctly increase the adsorption affinity of the linear molecular configurations of adsorbates by changing the adsorption orientations. The target N and S functionalities in f...

First-principles investigation of CO adsorption on pristine, C-doped and N-vacancy defected hexagonal AlN nanosheets

The optimized atomic structures, energetics and electronic structures of toxic gas CO adsorption systems on pristine, C-doped and N-vacancy defected h-AlN nanosheets respectively have been investigated using Density functional theory (DFT-D2 method) to explore their potential gas detection or sensing capabilities. It is found that both the C-doping and the N-vacancy defect improve the CO adsorption energies of AlN nanosheet (from pure −3.847 eV to −5.192 eV and −4.959 eV). The absolute value of the system band gap change induced by adsorption of CO can be scaled up to 2.558 eV or 1.296 eV after C-doping or N-vacancy design respectively, which is evidently larger than the value of 0.350 eV for pristine material and will benefit the robustness of electronic signals in potential gas detection. Charge transfer mechanisms between CO and the AlN nanosheet have been presented by the Bader charge and differential charge density analysis to explore the deep origin of the underlying electronic structure changes. This theoretical study is proposed to predict and understand the CO adsorption properties of the pristine and defected h-AlN nanosheets and would help to guide experimentalists to develop better AlN-based two-dimensional materials for efficient gas detection or sensing applications in the future.

Tuning patterning conditions by co-adsorption of gases: Br2 and H2 on Si(001)

We have studied the co-adsorption of Br2 and H2 on Si(001), and obtained co-adsorption energies and the surface phase diagram as a function of the chemical potential and pressure of the two gases. To do this, we have used density functional theory calculations in combination with ab initio atomistic thermodynamics. Over large ranges of bromine and hydrogen chemical potentials, the favored configuration is found to be either one with only Br atoms adsorbed on the surface, at full coverage, in a (3 × 2) pattern, or a fully H-covered surface in a (2 × 1) structure. However, we also find regions of the phase diagram where there are configurations with either only Br atoms, or Br and H atoms, arranged in a two-atom-wide checkerboard pattern with a (4 × 2) surface unit cell. Most interestingly, we find that by co-adsorbing with H2, we bring this pattern into a region of the phase diagram corresponding to pressures that are significantly higher than those where it is observed with Br2 alone. We also find small regions of the phase diagram with several other interesting patterns.

Incremental Gravimetry: A Method for Two-Parameter Model Building of Binary Gas Co-Adsorption Equilibria

This paper presents and develops a novel methodology to determine thermodynamic parameters of binary gas co-adsorption equilibria at given total pressure, based exclusively on binary gravimetric measurements at this same total pressure, together with single component isotherms. By “Incremental Gravimetry”, we designate a procedure in which the adsorbent sample is submitted to increments of composition of a flowing binary gas, and the corresponding increments of weight of the sample at equilibrium are measured. The experimental example is the co-adsorption of methane and carbon dioxide on Norit activated carbon near ambient temperature and pressure. The approach relies on the thermodynamics of non-ideal adsorbed solutions. The experimental methodology is described, the underlying theory is then presented. Compact analytical expressions are established that relate the measured limiting slopes of the incremental gravimetric curves (at infinite dilution of one component in the other) to quantities that derive only from the pure component isotherms, and to the infinite dilution activity coefficients. The latter are then uniquely determined. Classical two-parameter models for the composition dependence of activity coefficients are then implemented to reconstruct the complete binary isotherms and the incremental gravimetric curves. The comparison of the latter with the measured curves permits to test the different models.

Experimental and Numerical Investigation of Adsorption/Desorption in Packed Sorption Beds under Ideal and Nonideal Flows

The importance of the wall effect on packed beds in the adsorption and desorption of carbon dioxide, nitrogen, and water on molecular sieve 5A of 0.127 cm radius is examined experimentally and with one-dimensional computer simulations. Experimental results are presented for a 22.5-cm long by 4.5-cm diameter cylindrical column with concentration measurements taken at various radial locations. The set of partial differential equations is solved using finite differences and Newmanss method. Comparison of test data with the axial-dispersed, nonisothermal, linear driving force model suggests that a two-dimensional model (submitted to Separation Science and Technology) is required for accurate simulation of the average column breakthrough concentration. Additional comparisons of test data with the model provided information on the interactive effects of carrier gas coadsorption with CO2 as well as CO2─H2O interactions.

Rare gas coadsorption with Cs or K on Ag(111)

Rare gas (RG) coadsorption with submonolayer amounts of Cs or K on Ag(111) was studied using low-energy electron diffraction (LEED). A crossover in the alkali-RG interaction from repulsive to attractive was observed as a function of alkali species and of alkali coverage. The KRG interaction was observed to be repulsive at all coverages, while the CsRG interaction was observed to be attractive at low Cs coverages and apparently repulsive at high Cs coverages. For the K + RG adsorption system, desorption data were analyzed to determine the spreading pressure in the alkali layer, thus showing that RG can be used as a 2D manometer in some coadsorption systems. From the spreading pressure it is possible to obtain some information about the properties of the adsorbed alkali such as the energy differences between commensurate and incommensurate phases. We also demonstrate that work function measurements from such coadsorption systems do not necessarily have a simple interpretation.

ALKALI-METAL ADSORPTION ON COPPER AND NICKEL SURFACES

This paper reviews most of the experimental results for the submonolayer adsorption of alkali metals on copper and nickel surfaces, with emphasis on the structural findings. Where possible, comparisons are made between the overlayers on copper and those on nickel. The goal is to point out some of the most interesting recent structural results and to move toward a general understanding of these systems. The few structural results of coadsorption of gases with alkali metals are also described.

Calorimetric Investigations of Processes at the Solid/Gas Interphase

AbstractAdsorption calorimetry, partially combined with thermal desorption spectroscopy and isotope exchange measurements, has been used to study the adsorption and coadsorption of gases on metal films under ultrahigh vacuum conditions. It has proved to be possible to get detailed information on both the primary adsorption step and the consecutive reaction in the adsorbed layer. Adsorption of CO and CO2 on Fe are treated as examples with subsequent decomposition reactions. In the case of the coadsorption of CO and O2 and of H2 and CO on Fe the mutual interaction of the gases including replacement processes are studied.

Coadsorption d'éthylene et de krypton sur graphite à 68,85 K

The experimental studies devoted to the coadsorption of gases on graphite are mostly related to two gases with very diffcrerent 3D condensation properties and wetting properties. In these cases we always observe a displacement of the condensed imperfectly wetring two-dimensional layer by the perfectly wetting film according to a first-order phase transition. But with krypton and ethylene which are two gases with such properties at 68.85 K the results obtained by a volumetric method are very different : 1) krypton adsorption does not displace the ethylene layer and the krypton molecules adsorb on the preadsorhed ethylene layer ; 2) the first step of the krypton isotherms shows one or several vertical substeps corresponding to krypton adsorption on the two different structures of the ethylene film (low-density solid and high-density solid).

Desorption from Gas Covered Surfaces by Electron Impact: A Review of the Subject

Examples are given to indicate that interaction of electrons with surface gas layers is of considerable technological importance. A summary of the many significant measurements that have been made on electron impact desorption phenomena (EID) during the period 1967–1971 is presented. These include measurements of threshold electron energies for ion production, cross section, ion energy spectra, and mass analysis. Also discussed are the interesting effects caused by the coadsorption of gases and recent work showing the practicability of direct measurements of metastable and excited atoms ejected from the surface.