Adsorption Of Carbon Monoxide Research Articles

Unravelling the real active center for CO oxidation-Cu+ or Cu3+: A case of model LaCuO3/MCF

Cu-based catalysts are one of the promising alternatives for industrial carbon monoxide (CO) oxidation applications. However, the exact active sites as well as their natures for CO oxidation have been still not fully understood yet. Herein, we designed and constructed a nano-size LaCuO3 perovskite oxide supported on inactive mesocellular siliceous foam (MCF), in which, the Cu species is featured by Cu3+. Then, LaCuO3-y/MCF with abundant Cu+ species was obtained by treating the as-prepared LaCuO3/MCF in H2/N2 flow. The catalytic activities of LaCuO3/MCF and LaCuO3-y/MCF were investigated for CO oxidation. The experimental results revealed that the Cu+ species rather than Cu3+ was the reactive site for CO oxidation. Moreover, density functional theory (DFT) calculations uncovered that the Cu+ species not only considerably facilitated the adsorption of CO and O2, but also dramatically reduced the desorption energy of CO2 from defective surface, thereby enhancing the catalytic activity of CO oxidation over Cu+ notably.

Compressive Stress and Charge Redistribution during CO Adsorption Onto Pt

Electroorganic reactions, where energy is either stored or released from chemical bonds within carbon-based molecules, are essential to help achieve a circular carbon-based economy. Central to electrochemical conversion of organic molecules is carbon monoxide (CO), which serves as both an intermediate in electrochemical CO2 reduction to hydrocarbons and electrochemical oxidation in fuel cells that operate via oxygenated hydrocarbons (e.g., ethanol, methanol). For the latter, Pt has been the predominate catalyst of choice, and substantial effort has been spent to identify the mechanistic details for complete oxidation of alcohol-based fuels. With CO conversion serving as an important if not rate-limiting step of the oxidative process, it is critical to understand the state of a catalytic surface when CO is present.The change in surface stress associated with the adsorption and oxidative stripping of CO on (111)-textured Pt is examined using the wafer curvature method in 0.1 mol/L KHCO3 electrolyte.1 The curvature of the Pt cantilever electrode was monitored as a function of potential in both CO free and CO-saturated electrolyte. Although CO adsorbs as a neutral molecule, significant compressive stress, up to -1.3 N/m, is induced in the Pt. The magnitude of the stress change correlates directly with the CO coverage, and within the detection limits of the stress measurement, is elastically reversible. Density functional theory calculations of a CO bound Pt surface indicate that charge redistribution from the first atomic layer of Pt to subsurface layers account for the observed compressive stress induced by the charge neutral adsorption of CO. A better understanding of adsorbate-induced surface stress is critical for the development of materials platforms for sensing and catalysis. References D. Raciti, K.A. Schwarz, J. Vinson, and G.R. Stafford, The Journal of Physical Chemistry C , 126, 4446-4457 (2022).

Solar reduction of carbon dioxide on copper-tin electrocatalysts with energy conversion efficiency near 20%

Copper catalysts modified with tin have been demonstrated to be selective for the electroreduction of carbon dioxide to carbon monoxide. However, such catalysts require the precise control of tin loading amount. Here, we develop a copper/tin-oxide catalyst with dominant tin oxide surface being formed via a spontaneous exchange reaction between sputtered tin and copper oxide. Even though the surface of this catalyst is tin-rich, it achieves an excellent performance towards carbon monoxide production in a flow cell. This contrasts with copper/tin-oxide prepared via atomic layer deposition since it yields selectivity towards carbon monoxide only on a copper-rich surface. Mechanism studies reveal that the tin sites on the tin-rich copper/tin-oxide surface achieve a suitable binding with adsorbed carbon monoxide under the presence of copper. Powered by a triple-junction solar cell, the copper/tin-oxide based electrolyzer sets a new benchmark solar-to-chemical energy conversion efficiency of 19.9 percent with a Faradaic efficiency of 98.9 percent towards carbon monoxide under simulated standard air mass 1.5 global illumination.

H2 and CO adsorption ability of cationic lithiated carbenes: A computational study

Quantum chemical calculations have been carried out to investigate the hydrogen and carbon monoxide adsorption characteristics of cationic lithiated carbene complexes. Through the computation of electron density and electron−density−based reactivity descriptors, the nature of interactions related to the bonding between carbene and lithium as well as that between lithium and adsorbed H2 and CO are examined. Calculations reveal that the carbene−Li + complexes can absorb a maximum of four H2 molecules reaching a maximum gravimetric density of 8.8 wt%, whereas, it is found to reach a maximum of 41.3 wt% for the absorption of four CO molecules. The fate of H2 absorption in a carbene−Li+ complex has been studied in the course of a 2000 fs time evolution through Born−Oppenheimer Molecular Dynamics simulation at different temperatures. The outcomes reveal that the H2 molecules are strongly bound at 77 K and get slowly released at elevated temperature.

Theoretical investigation of CO oxidation by single cobalt atom within two-dimensional porphyrin sheet

In this paper, the oxidation mechanism of carbon monoxide (CO) on two-dimensional porphyrin sheet within a single cobalt atom (Co-TDPs) was studied by density functional theory with dispersion (DFT-D). The stability of Co-TDPs at different temperatures was verified by first-principle molecular dynamics simulations. Absorption energies of reactant and product to anchor to the Co–N4 site showed CO and O2 adsorption to be stronger than the CO2 adsorption. In addition, the Langmuir–Hinshelwood, Eley–Rideal (ER), and ter-molecular Eley–Rideal (TER) mechanisms were used to investigate the reaction mechanisms of CO oxidation on Co-TDPs. The Langmuir–Hinshelwood (LH) and ER mechanisms were feasible reaction profiles of CO oxidation because of their smaller energy barrier. The results suggested that the Co-TDPS was acting as a catalyst for CO oxidation in the mild condition.

Selective determination of Pd nanostructures in environmental matrices - Application of a carbon monoxide probe

The use of metallic platinum group metals (PGMs) increased the content of these metals in various elements of the environment. They undergo changes in the environment, become bioavailable and mobile and therefore dangerous. It is important to collect information not only about the total content of PGMs, but also about their chemical forms (which differ in eco-toxicity). Method based on quantification of CO adsorption on the surface of metallic Pd can be used for determination of its nanoparticles in water and plant tissue. It is highly reproducible (repeatability 2%) and not sensitive to the matrix effect (repeatability 10% in unprocessed plant extract). The limit of detection (LOD) equals 4.5 µg Pd-NPs, and can be easily lowered after reduction of the sample volume by evaporation. Adding low-temperature ultrasound-assisted dissolution of the sample in conc. nitric acid allows to distinguish Pd-NPs from Pt-NPs, but only if the contribution of Pd in the adsorption of carbon monoxide is higher than 7.5%.

The Underpotential Deposition of Lead and its Effect on Carbon Monoxide Adsorption on Pt(111) Electrode

In situ scanning tunneling microscopy (STM) was used to examine the spatial structures of lead (Pb) adatom and carbon monoxide (CO) molecule adsorbed onto an ordered Pt(111) electrode in 0.1 M perchloric acid (HClO4) containing 1 mM Pb(ClO4)2 under potential control. Ordered Pb structures were not seen until the potential was made more negative to 0 V (vs Ag/AgCl), where a quasi-square array (√7 × √57) was seen. Shifting the potential more negative substantiated Pb deposition, which triggered restructuring of the Pb adlayer into (√21 × √21)R11° and (3 × 2√3)rect (θ = 0.62 and 0.67) at −0.1 V. Pb adatom reduced the poisoning effect of CO on the Pt(111) electrode by blocking the adsorption of CO and by forcing CO molecule to asymmetric sites. An ordered (√7 × 3)—Pb + CO structure was imaged at 0 V in 0.1 M HClO4 + 1 mM Pb(ClO4)2, from which the surface coverage and binding sites of CO molecule were inferred.

Improved model of lattice gas in the adsorption of carbon monoxide and oxygen

The adsorption and subsequent oxidation of carbon monoxide (CO) on a platinum (Pt) surface has been studied using computational methods. The Monte Carlo method is used to this end through the lattice model. This study focuses on the improvement of this first theoretical model (ZGB) proposed for the oxidation of CO. In this work, four different models are revised in detail with the objective of establishing a comparison between the obtained results on the oxidation of CO on the Pt with an orientation (111) surface. The variance between the models lies on the nature of the sticking coefficient of the CO and oxygen (O2) molecules on Pt (111). This adsorption depends on the initial concentration of CO in the gas phase and the number of vacant sites on the platinum surface. The results obtained in these simulations show that the first model, the ZGB model, differs considerably from the other models, and thus the results with the second and third model have a better adjustment to the adsorption of the CO and O2 molecules, since they take into account the gas concentration, the sticking coefficient and the interaction with the neighboring particles. In this sense, the oxidation reaction occurs in a wider theoretical range around 0.5 mole fraction of CO and 0.2 mole fraction of O atomic, and the poisoning of the platinum catalytic surface can be inhibited if the concentration of carbon monoxide is included as a control parameter.

Modeling Electrochemical Processes with Grand Canonical Treatment of Many-Body Perturbation Theory.

Electrocatalysis plays a key role in sustainable energy conversion and storage. It is critical to model the grand canonical treatment of electrons, which accounts for the electrochemical potential explicitly, at the atomic scale and understand these reactions at electrified interfaces. However, such a grand canonical treatment for electrocatalytic modeling is in practice restricted to a treatment of electronic structure with density functional theory, and more accurate methods are in many cases desirable. Here, we develop an original workflow combining the grand canonical treatment of electrons with many-body perturbation theory in its random phase approximation (RPA). Using the potential dependent adsorption of carbon monoxide on the copper (100) facet, we show that the grand canonical RPA energetics provide the correct on-top Cu geometry for CO at reducing potential. The match with experimental results is significantly improved compared to the functionals at the generalized gradient approximation level, which is the most commonly used approximation for electrochemical applications. We expect this development to pave the way to further electrochemical applications using RPA.

Direct Visualisation of the Surface Atomic Active Sites of Carbon-Supported Co3 O4 Nanocrystals via High-Resolution Phase Restoration.

The atomic arrangement of the terminating facets on spinel Co3O4 nanocrystals is strongly linked to their catalytic performance. However, the spinel crystal structure offers multiple possible surface terminations depending on the synthesis. Thus, understanding the terminating surface atomic structure is essential in developing high‐performance Co3O4 nanocrystals. In this work, we present direct atomic‐scale observation of the surface terminations of Co3O4 nanoparticles supported on hollow carbon spheres (HCSs) using exit wavefunction reconstruction from aberration‐corrected transmission electron microscopy focal‐series. The restored high‐resolution phases show distinct resolved oxygen and cobalt atomic columns. The data show that the structure of {100}, {110}, and {111} facets of spinel Co3O4 exhibit characteristic active sites for carbon monoxide (CO) adsorption, in agreement with density functional theory calculations. Of these facets, the {100} and {110} surface terminations are better suited for CO adsorption than the {111}. However, the presence of oxygen on the {111} surface termination indicates this facet also plays an essential role in CO adsorption. Our results demonstrate direct evidence of the surface termination atomic structure beyond the assumed stoichiometry of the surface.

Understanding the complementarities of surface-enhanced infrared and Raman spectroscopies in CO adsorption and electrochemical reduction

In situ/operando surface enhanced infrared and Raman spectroscopies are widely employed in electrocatalysis research to extract mechanistic information and establish structure-activity relations. However, these two spectroscopic techniques are more frequently employed in isolation than in combination, owing to the assumption that they provide largely overlapping information regarding reaction intermediates. Here we show that surface enhanced infrared and Raman spectroscopies tend to probe different subpopulations of adsorbates on weakly adsorbing surfaces while providing similar information on strongly binding surfaces by conducting both techniques on the same electrode surfaces, i.e., platinum, palladium, gold and oxide-derived copper, in tandem. Complementary density functional theory computations confirm that the infrared and Raman intensities do not necessarily track each other when carbon monoxide is adsorbed on different sites, given the lack of scaling between the derivatives of the dipole moment and the polarizability. Through a comparison of adsorbed carbon monoxide and water adsorption energies, we suggest that differences in the infrared vs. Raman responses amongst metal surfaces could stem from the competitive adsorption of water on weak binding metals. We further determined that only copper sites capable of adsorbing carbon monoxide in an atop configuration visible to the surface enhanced infrared spectroscopy are active in the electrochemical carbon monoxide reduction reaction.

CO oxidative coupling with nitrite to oxalate over palladium catalyst: A comprehensive kinetic modeling

Oxidative coupling of carbon monoxide (CO) with methyl nitrite (MN) to dimethyl oxalate (DMO) on the Pd/α-Al2O3 catalyst is a vital step for ethylene glycol (EG) and glycolic acid (GA) production from syngas. In this work, we revisited the reaction mechanism and kinetics by including the side reactions to dimethyl carbonate (DMC) and methyl formate (MF). Based on the Langmuir–Hinshelwood (LH) mechanisms, kinetic models were proposed, coupling pathways occurring between two Pd-COOCH3 (Pathway 1) or between Pd-CO and Pd-COOCH3 (Pathway 2). Among them, the LH mechanism with dissociation of MN based on Pathway 1 illuminated the overall reaction best. In addition, the coupling reactions of adsorbed CH3OCO governed the reaction pathways for DMO, and the hydrogenation of CH3OCO for MF. The model reveals that the strongly competitive adsorptions of both CO and NO at high concentrations will suppress the reaction. Overall, the followed kinetic analysis accurately predicted and explained the experimental data. The resulted best-fit model applies to reactor simulation, with satisfactory agreement with three pilot-scale fixed-bed reactors disclosed in the literature by adjusting only the activity coefficient. Therefore, this comprehensive kinetic modeling can be a solid foundation for reactor design and retrofit and operation optimization.

Overview of Carbon Monoxide Adsorption Performance of Pristine and Modified Adsorbents

Carbon monoxide (CO) is a key material in C1 chemistry for chemical production and CO2 reduction, whereas in applications, such as H2 for fuel cells, its concentration must be kept below 0.2 ppm. Adsorption technology is useful for both CO removal and production to provide environmental sustainability for the energy and chemical industries. In this review, the CO adsorption performances of various adsorbents, such as activated carbons, zeolites, metal–organic frameworks, activated alumina, mesoporous silicas, and their modified adsorbents, are collected, and their physical and chemical properties and CO selectivities are summarized. Cu+ impregnation is a powerful and widely used modification method to enhance the CO adsorption of adsorbents. Therefore, the preparation methods and their effects on CO adsorption are also compared and reviewed. The data and analysis in this review can provide insights for the development of novel adsorbents and processes for CO removal and production.

Computational and structural study of titanium/carbon nanotube nanocomposite

In this study, the electronic structure and thermodynamic parameters of titanium doping at different locations of carbon nanotubes (6-6) have been investigated using density functional theory computational methods. The Ti prefers to be located near to vertex of the nanotube sidewall and at the central axis and leads to better structural stability and thermodynamic parameters than other sites. Then, the most stable and active structure for carbon monoxide adsorption was examined from two directions of oxygen and carbon atom, which is accompanied by hybridization and spatial repulsion. The results obtained from the energy level of the highest occupied HOMO orbital and the lowest occupied LUMO one and also NBO analysis indicated that the electron-accepting titanium metal (Mulliken charge for titanium atom above 0.5) has an empty orbital. Carbon monoxide gas is a donor of electron pairs. The adsorption of carbon monoxide from the oxygen atom side in the vertical state (IVA) on the surface of the nanotube doped with titanium was found to be the best.

Functionalized graphene-based Quantum Dots: Promising adsorbents for CO, NO2, SO2, and NH3 Pollutant Gases

The development of more sensitive and accurate sensors is essential to monitor the levels of pollutant gases that are causing high damage to the biosphere. One of the most promising materials for such application is graphene, which, due to its extensive collection of properties, has shown itself capable of adsorbing gas molecules. Thus, the present work aims to investigate the adsorption of carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and ammonia (NH3) on Graphene Quantum Dots (GQD) through electronic structure and molecular dynamics calculations. The data suggest doping GQDs with boron, nitrogen, or aluminum can greatly improve their adsorbing capabilities. For both CO and NH3, a functionalization with aluminum is the most effective, while the adsorption of SO2 was not much affected by any of the doping designs. Notably, quantum dots doped with all three heteroatoms are extremely promising with respect to the application in NO2 gas sensors. Thereby, the results indicate that accurate and resilient gas sensors based on doped GQDs may be a good substitute for the current sensors in the market.

Cu(I)-loaded boehmite microspheres prepared by the continuous flow-assisted spray-drying method for selective carbon monoxide separation

An efficient and low-cost adsorbent material is necessary for separating carbon monoxide (CO) from off-gases that also contain CO2 and N2. Boehmite (γ-AlOOH)-based materials have shown great potential for many applications. In this work, mesoporous γ-AlOOH microspheres were rapidly produced by combining the sol–gel and continuous flow-assisted spray-drying methods (SD-AlOOH). Then, Cu(I) chloride (CuCl) was thermally dispersed into the SD-AlOOH microspheres to obtain the CuCl@SD-AlOOH adsorbent. Gas adsorption experiments revealed that the CuCl@SD-AlOOH samples adsorbed CO over CO2 and N2 owing to the π-complexation reaction between CO and Cu(I). The adsorption properties were affected by the spray-drying conditions, CuCl load, and CuCl dispersion temperature. The optimal SD-AlOOH, which was loaded with 33 wt% CuCl, exhibited a CO adsorption capacity of ∼38.7 cm3 g−1 (25 °C and 100 kPa), which exceeds that of commercial CuCl-loaded AlOOH and many other Cu(I) π-complexation adsorbents. Furthermore, the prepared CuCl@SD-AlOOH showed high ideal adsorbed solution theory (IAST)-predicted CO/CO2 and CO/N2 selectivities of ∼87 and ∼730, respectively, at 100 kPa. Breakthrough tests showed that the CuCl-loaded SD-AlOOH microspheres effectively separated CO from a gas mixture with CO2 under dynamic flow conditions.

Preparation of Aluminum-Molybdenum Alloy Thin Film Oxide and Study of Molecular CO + NO Conversion on Its Surface.

Adsorption and interaction of carbon monoxide (CO) and nitric oxide (NO) molecules on the surface of bare Al-Mo(110) system and on that obtained by its in situ oxidation have been studied in ultra-high vacuum (base pressure: ca. 10−8 Pa) by means of Auger and X-ray photoelectron spectroscopy (AES, XPS), low energy electron diffraction (LEED), reflection–absorption infrared and thermal desorption spectroscopy (RAIRS, TDS), and by the work function measurements. In order to achieve the Al-Mo(110) alloy the thin aluminum film of a few monolayers thick was in situ deposited onto the Mo(110) crystal and then annealed at 800 K. As a result of Al atoms diffusion into the Mo(110) subsurface region and the chemical reaction, the surface alloy of a hexagonal atomic symmetry corresponding to Al2Mo alloy is formed. The feature of thus formed surface alloy regarding molecular adsorption is that, unlike the bare Mo(110) and Al(111) substrates, on which both CO and NO dissociate, adsorption on the alloy surface is non-dissociative. Moreover, adsorption of carbon monoxide dramatically changes the state of pre-adsorbed NO molecules, displacing them to higher-coordinated adsorption sites and simultaneously tilting their molecular axis closer to the surface plane. After annealing of this coadsorbed system up to 320 K the (CO + NO → CO2 + N) reaction takes place resulting in carbon dioxide desorption into the gas phase and nitriding of the substrate. Such an enhancement of catalytic activity of Mo(110) upon alloying with Al is attributed to surface reconstruction resulting in appearance of new adsorption/reaction centers at the Al/Mo interface (steric effect), as well as to the Mo d-band filling upon alloying (electronic effect). Catalytic activity mounts further when the Al-Mo(110) is in situ oxidized. The obtained Al-Mo(110)-O ternary system is a prototype of a metal/oxide model catalysts featuring the metal oxides and the metal/oxide perimeter interfaces as a the most active reaction sites. As such, this type of low-cost metal alloy oxide models precious metal containing catalysts and can be viewed as a potential substitute to them.

Influence of Defects and Heteroatoms on the Chemical Properties of Supported Graphene Layers

A large and growing number of theoretical papers report the possible role of defects and heteroatoms on the chemical properties of single-layer graphene. Indeed, they are expected to modify the electronic structure of the graphene film, allow for chemisorption of different species, and enable more effective functionalisation. Therefore, from theoretical studies, we get the suggestion that single and double vacancies, Stone–Wales defects and heteroatoms are suitable candidates to turn nearly chemically inert graphene into an active player in chemistry, catalysis, and sensoristics. Despite these encouraging premises, experimental proofs of an enhanced reactivity of defected/doped graphene are limited because experimental studies addressing adsorption on well-defined defects and heteroatoms in graphene layers are much less abundant than theoretical ones. In this paper, we review the state of the art of experimental findings on adsorption on graphene defects and heteroatoms, covering different topics such as the role of vacancies on adsorption of oxygen and carbon monoxide, the effect of the presence of N heteroatoms on adsorption and intercalation underneath graphene monolayers, and the role of defects in covalent functionalisation and defect-induced gas adsorption on graphene transistors.

Comparative study on adsorption behaviour of the monolayer graphene, boron nitride and silicon carbide hetero-sheets towards carbon monoxide: Insights from first-principle studies

A comprehensive study on the sensitivity of graphene, boron nitride, silicon carbide and their in-plane hetero-sheets towards carbon monoxide (CO) was performed using first-principle density functional theory calculations. To rationalize the CO adsorption on pristine and hetero-sheets, molecular electrostatic potential contours, HOMO-LUMO distributions, the density of states plots, atomic charge distributions and quantum chemical descriptors were calculated. The optimized geometries showed that the CO molecule oriented itself at different angles with respect to sheets. A shift in the characteristic vibrational frequency of CO was observed through theoretically computed infra-red spectra. The maximum shift was observed for the GRA/SiC hetero-sheet. Charge analysis showed the partial charge transfer from the CO molecule to the adsorbent sheets. This was further confirmed by the HOMO-LUMO distributions of the interacting species. The reactivity descriptors calculated based on the HOMO-LUMO energies, molecular electrostatic potential contours and DOS plots showed that GRA/SiC hetero-structure exhibited better sensitivity towards CO than other sheets. The calculated adsorption energies, corrected for basis set superposition error, ranged from −3 to −10 kJ mol−1, confirming the physical nature of adsorption.

Unraveling the Interfacial Polarization Effect between Pd and Polymeric Carbon Nitride toward Efficient CO2 Electroreduction to CO.

The efficient electrochemical conversion of carbon dioxide (CO2) to carbon monoxide (CO) using renewable energy is an effective route to pursue carbon neutrality. Optimizing the binding energy of CO on palladium (Pd) metal-based materials used in this process is to make sure the timely desorption of CO from their active sites is critical. Tuning the electronic structure of the Pd center is an effective strategy to optimize its catalytic performance. Herein, we rationally design Pd nanoparticles (NPs)/polymeric carbon nitride (CN) (Pd/CN) composite, which alters the electronic structure of Pd by introducing the interfacial polarization effect to accelerate CO desorption and improve CO selectivity of Pd catalyst. The optimized Pd/CN exhibits a CO Faradaic efficiency of 92.7% at -0.9 V versus reversible hydrogen electrode in CO2-saturated 0.1 M KHCO3 solution. Experimental investigations and theoretical calculations jointly confirm that the enhanced CO selectivity and stability originate from the electron transfer at the Pd/CN interface, and the weakened *CO adsorption on the palladium hydride surface.