Subsurface Adsorption Research Articles

Basin modelling workflow applied to the screening of deep aquifers for potential CO 2 storage

The temporal and spatial scale of interest of CO 2 storage studies lies in between reservoir and basin models. While reservoir modelling software is best fitted to address some of the multiphysics issues related to the behaviour of CO 2 once injected into the subsurface (adsorption, dissolution, near injection wellbore mechanics and temperature, and, in some cases, fluid rock interaction) within a human timescale, basin modelling tools handle better the full basin volume and time-scale heterogeneities that impact the storage potential and risk associated with CO 2 injection. This study takes a basin modelling approach to provide an assessment of the influence of geological evolution on CO 2 storage capacity, both at the reservoir level, by helping to estimate the amount of CO 2 that can be stored in its connected porosity, and at the cap-rock level, by assessing the seal integrity. Our basin model also captures the evolution of the pressure plume induced by the CO 2 injection, taking into account the pressure and temperature fields, aquifer connectivity and permeability, and seal integrity, on a much shorter timescale than is usually considered by such a model. The results show the impact of basin evolution on aquifer properties and consequently on the dissipation of the induced pressure plume. They also highlight the large-scale influence of the CO 2 on the pressure field both vertically along the stratigraphic column, when the pressure plume reaches shallower aquifers through unconformities, and horizontally, when good aquifer injectivity and connectivity allows the pressure plume to dissipate widely.

Hydrogen diffusion on (100), (111), (110) and (211) gold faces

AbstractCalculations showed that hydrogen adsorption into subsurface sites is most likely to occur on Au (110) and (211) faces. The presence of low‐coordinated Au atoms on significantly reduces the barrier of subsurface adsorption of H. The barriers of H surface diffusion increase in the following Au series: (110) < (111) < (100) < (211). An analysis of the dependence of the surface diffusion barriers on the electronic structure of gold atoms on the respective faces revealed a U‐shaped dependence of the centers of the s‐ and d‐bands. This dependence is the result of the filling of the s‐ and d‐bands on different faces of the gold. The results obtained suggest that it is possible to use band centers to determine surface diffusion barriers.

Comparative study of methane adsorption of Middle-Upper Ordovician marine shales in the western Ordos Basin, NW China: Insights into impacts of moisture on thermodynamics and kinetics of adsorption

Impacts of water molecules on subsurface shale gas adsorption is a challenging topic in the assessment of shale gas resources and the selection of optimized exploitation plans. And scholars have recognized that water molecules occupy adsorption sites on hydrophilic pore walls. However, the impacts of water molecules on the thermodynamics and kinetics of methane adsorption in shales remains poorly understood. We document a series of high-pressure methane adsorption isotherms of dry and moisture-equilibrated samples of the Middle-Upper Ordovician Wulalike shale at 20–120 °C and up to 30 MPa. Quantitative analyses of the thermodynamic and kinetic characteristics are carried out. Results show that water molecules do not change the impacts of temperature and pressure on the trend of isotherms, thermodynamics, and kinetics of methane adsorption. The impacts of temperature, pressure, methane adsorption capacity, and water molecules on the methane adsorption are basically functioned by modifying the interactions between the adsorbate and the adsorbent. The presence of water molecules in shales leads to a decrease of ∼ 77.06% in the capacity of methane adsorption, an increase of ∼ 70.46% in the adsorption heat (Qst), a decrease of ∼ 96.62% in the standard entropy (△S0), and a decrease of ∼ 1/9 to 1/5 in the Bangham adsorption rate (kb). The impacts of water molecules on the decline of methane adsorption at high pressure is lower than that at low pressure, however, on the decrease of methane adsorption rate higher than that at low pressure. The study also reflects the methane adsorption into the three-dimensional network system of kerogen. This work can improve our understanding of subsurface supercritical adsorption under reservoir conditions.

Insight into Subsurface Adsorption Derived from a Lattice-Gas Model and Monte Carlo Simulations

Insight into Subsurface Adsorption Derived from a Lattice-Gas Model and Monte Carlo Simulations

On the origin of the high-temperature desorption of subsurface hydrogen from Ni (1 1 0)

It has been demonstrated that the catalytic hydrogenation of CH3, C2H2 and CO that takes place on Ni single crystals, occurs almost exclusively by subsurface atomic hydrogen (H), indicating the importance of bulk hydrogen in heterogeneous catalysis. Here, we use Density Functional Theory (DFT) calculations to investigate the ability of, the H induced, 1x2 reconstruction of Ni (110), to adsorb additional H in the subsurface area and we compare with the clean surface. Our results suggest that the formation of the Ni 1x2 phase on Ni (110), results in the creation of stable subsurface adsorption sites for atomic H. The reversal of the thermodynamic drive on H atoms that are adsorbed on the catalyst surface, occurs during the transition between the 1x1 and 1x2 surface phases. This reversal, of the thermodynamic drive, leads to the creation of subsurface atomic H that desorbs above RT. This study provides an explanation regarding the high temperature desorption of subsurface H from Ni (110) that was reported previously in the literature and a consistent interpretation of the experimental results related to it.

Synergistic catalytic ozonation of toluene with manganese and cerium varies at low temperature

The temperature of waste gas in refuse transfer station, airport smoking area, and RTO terminal is low, which needs deep oxidation. Catalytic ozonation is one of the most effective treatment techniques in these scenarios. In this study, we reported that catalysts were modified under the condition of magnetic field to simulate the low temperature dynamic conditions of low concentration toluene for catalytic ozonation. This paper aims to explore the relationship between oxygen vacancy and active oxygen species, and the specific pathways of toluene oxidation. The study found that citric acid can enhance the synergistic effect between Mn and Ce, and promote the generation of oxygen vacancies. The surface molecule adsorption oxygen is more conducive to catalytic oxidation than subsurface atom adsorption oxygen. Finally, we proposed the main pathways of toluene in this reaction system, which runs through the whole process of the reaction.

Experimental investigation on the effects of clay colloid-facilitated ammonium transport through saturated porous media under variable transport conditions

Ammonium contamination is one of the major environmental issues in subsurface contamination and groundwater which in turn poses risks to human health. Predicting and formulating desirable situations is necessary for the study of NH4+ ion adsorption and transport in the environment. The purpose of the present paper is to assess the influence of various factors, such as different colloidal concentration, different size of porous media and different flow rates on colloid-facilitated NH4+ ion transport. In order to understand the influence of colloid concentration on NH4+ ion transport in porous media, few soil column experiments were performed in laboratory scale. Different clay colloidal concentrations with NH4+ ion solution as contaminant were supplied to the soil column and the leached out solution was tested using UV–vis spectrophotometer to find the concentration of NH4+ ion; 500ppm clay colloidal concentration in fine sand medium at 5ml/min flow rate has been identified as most suitable condition for NH4+ ion subsurface adsorption with highest cumulative NH4+ ion adsorption of 1.9mg/g, whereas 200ppm clay colloidal solution had least cumulative NH4+ ion adsorbed values than other solutions. TherefoZhangre, 200ppm colloid solution was found to be most efficient for NH4+ ion transport. The efficiency of NH4+ ions transport in all the solutions in the study was doubled at a flow rate of 15ml/min than at 5ml/min. The outflow NH4+ ion concentration was lower for fine sand than medium sand in all the cases in the study. The results illustrated that variable factors in the study can either facilitate or retard ammonium ion adsorption.

Nanoscale surface reactions by laser irradiation of Al nanoparticles on MoO3 flakes

Surface reactions between heated aluminum nanoparticles (Al NPs) and thin α-MoO3 sheets are investigated. Localized photothermal heating on Al NP clusters is provided by a Raman spectrometer laser, while enhanced heating rates and imaging resolution are enabled by the use of a plasmonic grating substrate. Prominent linear reaction zones extending from Al NPs in the 〈001〉 crystal direction are observed on the surface of the host MoO3 sheets after heating. Raman spectroscopy and x-ray diffraction indicate that α-Al2O3 is generated within these extended reacted regions, while AFM and SEM indicate that the topology of the reaction regions are indistinguishable from the MoO3 host. We hypothesize that these Al2O3 zones are formed by surface diffusion and subsequent sub-surface adsorption of heated Al adatoms along the low-energy 〈001〉 MoO3 direction. Understanding and controlling these reaction mechanisms could lead to enhanced combustion of Al/MoO3 nanothermite systems.

Annual and diurnal water vapor cycles at Curiosity from observations and column modeling

Local column precipitable water contents (PWC) for more than a martian year from 113 Curiosity ChemCam passive-mode sky scans were used to force a column model with subsurface adsorption. ChemCam volume mixing ratios (vmr) and T, RH and vmr from REMS-H were compared with model results. The REMS-H observations point to decrease of vmr (i.e. depletion of near-surface water vapor) during every evening and night throughout the year. The model's pre-dawn results are quite similar to the REMS-H observations, if adsorption is allowed. The indicated porosity is about 30% and the night depletion ratio about 0.25. If adsorption is not allowed, RH and vmr become excessive during every night at all seasons, leading to ground frost between Ls 82°–146°; frost has not been observed. As brine formation is unlikely along the Curiosity track, adsorption thus appears to be the depleting process.During daytime the ChemCam vmr is in general close to surface values from the Mars Climate Database (MCD) vmr profiles for the Curiosity site when those profiles are scaled to match the ChemCam PWC. Our simulated daytime surface-vmr is in turn close to the ChemCam vmr when moisture is assumed well-mixed to high altitudes, whereas a low moist layer (15 km) leads to overestimates, which are worse during the warm season. Increased TES-like regional PWC also leads to large overestimates of daytime surface-vmr. Hence the crater appears to be drier than the region surrounding Gale and the results support a seasonally varying vertical distribution of moisture with a dry lower atmosphere (by Hadley circulation), as suggested by MCD and other GCM experiments.

Electrical and NO2 sensing characteristics of Pd/ZnO nanoparticles based Schottky diode at room temperature

The present work deals with Pd/ZnO nanoparticles based Schottky diode for detection of NO2 at room temperature (298 K). To fabricate Pd/ZnO Schottky diode, zinc oxide (ZnO) nanoparticles (NPs) based film was developed on glass substrate using sol-gel spin coating process. Subsequently; Pd was deposited on ZnO using thermal evaporation technique. The structural properties of developed ZnO film were studied using energy dispersive x-ray spectroscopy (EDS), x-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The particles size of the developed film was in range of ~25 to ~110 nm. The response of fabricated Pd/ZnO Schottky diode was studied upon exposure to NO2 in terms of change in I–V characteristics. The magnitude of barrier height and ideality factor has been evaluated with concentration of NO2 ranging from 10 to 50 ppm. The developed sensor has good sensitivity of ~45.2%, with fast response and recovery time; 67 s and 250 s respectively for 50 ppm concentration of NO2 with excellent repeatability. The obtained results have been explained in terms of surface and subsurface adsorption of NO2 on Pd, subsequently dissociation of NO2 and its diffusion, which creates dipole moment at the Pd/ZnO interface.

Atomic oxygen adsorption on Pb(1 0 0)

We study atomic oxygen adsorption on a Pb(1 0 0) surface using density functional theory. The structures, binding energies, work function, and charge transfer of on-surface and subsurface adsorption are investigated at a range of coverages from 0.06 to 1.00 ML. The energetically favored adsorption site for on-surface adsorption is found to be a distorted hollow site for the whole coverage range studied. The distorted structures are stabilized by mixing of 6s and 6p states of lead mediated by the 2p states of oxygen. For subsurface adsorption, the sub-bridge site is found to be preferred to the sub-hollow site at low coverages, the two being nearly equal in energy at monolayer coverage. At 0.11 ML coverage, diffusion from an on-surface hollow site to a sub-bridge site is found to be barrierless, suggesting facile subsurface oxidation at low coverages. Combined on-surface and subsurface adsorption leads to the formation of a two-layer oxide structure resembling β-PbO.

Highly sensitive NO2 sensor using brush-coated ZnO nanoparticles

This work reports the sensing properties of a ZnO nanoparticle (NP) based gas sensor. A sol-gel method was used for the synthesis of ZnO nanoparticles, and a brush coating technique for applying these in a thick film over the gold electrode. The structural properties of the ZnO film so developed have been studied using energy dispersive x-ray spectroscopy (EDS), x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), revealing a hexagonal wurtzite structure having particle size of ~25 to ~110 nm and roughness of ~136.303 nm. The sensitivity of the sensor to NO2, H2, CO, ethanol and propanol gases in the temperature range from 150 to 350 °C has been tested. Among all these gases, sensitivity to NO2 was found to be highest, at around fifty times greater than the next highest sensitivity, for ethanol gas. The sensor’s response to NO2 gas has been measured at ~945.12%/ppt (parts per thousand), with fast response time and recovery time at operating temperature 280 °C. The obtained result has been discussed with the help of surface and subsurface adsorption and desorption of NO2 molecules at the available trap sites (oxygen ions) on the ZnO nanoparticle surface. This sensor also exhibits excellent repeatability.

Optimized hydrogen sensing characteristic of Pd/ZnO nanoparticles based Schottky diode on glass substrate

The present work deals with the development of the Pd/ZnO naoparticles based sensor for detection of hydrogen (H2) gas at relatively low temperature (75–110 °C). Pd/ZnO Schottky diode was fabricated by ZnO nanoparticles based thin film on glass substrate using sol-gel spin coating technique. These ZnO nanoparticles have been characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive x-ray spectroscope (EDS), and field emission scanning electron microscope (FE-SEM) which reveals the ZnO film having particles size in the range of ~25 to ~110 nm with ~52.73 nm surface roughness. Gas dependent diode parameters such as barrier height and ideality factor have been evaluated upon exposure of H2 gas concentration in the range from 200–2000 ppm over the temperature range from 75 to 110 °C. The sensitivity of the Pd/ZnO sensor has been studied in terms of change in diode forward current upon exposure to H2 gas. Experimental result shows the optimized sensitivity ~246.22% for H2 concentration of 2000 ppm at temperature 90 °C. The hydrogen sensing mechanism has been explained by surface and subsurface adsorption of H2 molecules on Pd surface; subsequently, dissociation of H2 molecules into H + H atoms and diffusion to trap sites (oxygen ions) available on ZnO surface, resulting in formation of dipole moments at Pd/ZnO interface. The variation in the sensitivity, response and recovery time with temperature of Pd/ZnO sensor has also been studied.

Oxygen adsorption at heterophase boundaries of the oxygenated Cu(110)

Many metal-oxygen systems involve progressive stages of oxygen chemisorption induced surface phase transition and restructuring that result in the formation of heterophase boundaries within the oxygen chemisorbed layer. Using the density functional theory calculations, we investigated the effect of such heterophase boundaries formed by the (2 × 1)-O → c(6 × 2)-O phase transition on Cu(110) on the onset of bulk oxidation. Upon the increased oxygen coverage, we show that some (2 × 1)/(6 × 2) boundaries allow for further propagation of the (2 × 1)/(6 × 2) phase boundary while the other boundaries promote subsurface oxygen adsorption that results in the formation of Cu2O-like tetrahedrons. By comparing the surface height of the Cu atoms within the heterophase boundary area, we show that the boundaries with a larger surface elevation of the Cu atoms are prone to form Cu2O-like tetrahedrons by subsurface oxygen occupancy. These results indicate that the presence of the two-phase boundaries formed by the surface phase transition in the oxygen chemisorbed layer facilitates the inward diffusion of oxygen atoms and thus initiates the onset of bulk oxidation.

Density functional study of O2 molecule and O atom adsorption on α-U(0 0 1) surface

First-principle calculations have been performed to study both O2 molecule and O atom adsorption on α-U(001) surface and subsurface. The results show that the long-bridge site is the most stable adsorption site for O2U(001) and OU(001) surface adsorption. The tetrahedral (Tet) 1 site is the most stable adsorption site for OU(001) subsurface adsorption. The partial electronic density of states (PDOSs) of O2U(001) and OU(001) shows the hybridization of U and O atoms orbitals causes the electrons of 5f/6d of U more non-local and leads to the formation of OU bond. The OU bond is partly ionic and partly covalent. The analysis of the diffusion path of O atom on U(001) shows that O atom can easily transfer from hollow (hol) 1 site to hollow 2 site with no energy barrier. O atom can hardly transfer from surface to the subsurface.

Influences of the Pb 6s2 lone pair effect and quantum size effect on the diffusion of oxygen atoms on Pb(111) films

Based on our previous studies revealing quantum oscillations in the adsorption energetics of atomic oxygen on Pb(111) films, here we study all the possible on-surface and subsurface adsorption sites of oxygen atoms on Pb(111) films at different coverages.

The onset of sub-surface oxidation induced by defects in a chemisorbed oxygen layer

We investigate the onset of internal oxidation of a Cu(110) surface induced by oxygen subsurface adsorption via defects in the Cu(110)-(2 × 1)-O chemisorbed layer. The presence of a boundary formed by merged add-row structure domains due to a mismatch of half unit-cell leads to preferred oxygen adsorption at the subsurface tetrahedral sites. The resulting distorted Cu-O tetrahedra along the domain boundary have comparable bond length and angles to those of the bulk oxide phase of Cu2O. Our results indicate that the presence of defects in the oxygen-chemisorbed adlayer can lead to the internal oxidation via the formation of Cu2O-like tetrahedra in between the topmost and second outermost atomic layers at the oxygen coverage θ = 0.53 and the second and third outermost atomic layers at θ = 0.56. These results show that the internal oxidation of a metal surface can occur in the very beginning of the oxygen chemisorption process enabled by the presence of defects in the oxygen chemisorbed layer.

The origin of the site preference of H adsorption on Pd(100)

Spin-polarized density functional theory (DFT) calculations are carried out to determine the site preference of H adsorption on Pd(100) surface and subsurface. We carefully scrutinize the energy difference between different patterns at θ=0.50 ML and confirm the LEED observation that surface adsorption can form c(2×2) ordering structure. On the contrary, we disclose that p(2×1) structure become more favorable than c(2×2) for subsurface adsorption. These site preferences are rationalized via an analysis of the layer and orbital resolved density of states. Furthermore, we propose that the interstitial charge as a key factor determining the preferred H adsorbed site.

Application of quasi-equilibrated thermodesorption of linear and di-branched paraffin molecules for detailed porosity characterization of the mono-layered zeolite MCM-56, in comparison with MCM-22 and ZSM-5.

The pore characteristics of zeolite samples including two kinds of ZSM-5 crystals as a base case and the unique mono-layered MCM-56 in different structural forms have been studied by the new method QE-TPDA (quasi-equilibrated temperature-programmed desorption and adsorption) in comparison with the standard nitrogen adsorption. Both approaches produce consistent results in terms of micro- and meso-porous features as well as quantitative pore volume values. The benefits of QE-TPDA include fast data acquisition (hours) and small sample size (milligrams). It is very flexible in using various hydrocarbons as probe molecules, which may reveal additional details associated with pores, their internal environment and dimensions/shape of the sorbate molecules. Hence, QE-TPDA is a valuable complementary tool for porosity characterization of the ever increasing diversity of porous materials and their pore structures. This was demonstrated by the results for the desorption of nonane and 2,2-dimethyloctane (DMO). The latter showed an additional maximum in the intermediate temperature range (between 'micro-' and 'mesopore' regions) which could be attributed to adsorption in the subsurface micropores (i.e. the pore mouths) where DMO could be partially adsorbed with t-butyl groups remaining on the outside. This was also reflected in the discrepancy between apparent volumes of micro- and mesopores calculated from the nonane and DMO experiments. Pillared MCM-56 revealed visibly enhanced subsurface micropore adsorption compared to the parent (mono-layer MWW) and MCM-22 (multi-layered MWW) consistent with the expected increase in the content of external 12 ring surface cups.

First principles investigation of Ti adsorption and migration on Si(100) surfaces

The titanium adsorption on Si(100) is investigated using first principles computer modelling methods. Two new subsurface adsorption sites are described. They are located at the edge of the cavity topped by a surface silicon dimer. The migration of the titanium from the surface to the subsurface sites is facilitated when occurring via one of these sites. The ejection of one of the silicon atoms forming the surface dimer is also investigated. The actual step of the ejection requires more energy than previously thought although, when considering the global picture of a titanium atom on the surface leading to the ejection of a silicon atom, the overall rate is compensated by the facilitated migration of the titanium to the subsurface sites. The consecutive adsorption of a second and third titanium atom is also investigated. It is shown that titanium grows evenly on the surface in normal condition, showing no intermixing of the titanium and silicon beyond the silicon layer.