Infrared studies of the effect of acetylene, hydrogen, and oxygen on CO adsorption on platinum hydrosols

Infrared spectra of CO-treated platinum hydrosols subsequently treated with acetylene, hydrogen, and oxygen reveal that v(CO)_ads decreases from 2070 cm⁻¹ with increasing gas-treatment time. This has been attributed to a reduction in the coverage of adsorbed CO. In Pt sol/CO/C₂H₂ systems, v(CO)_ads decreases to a limiting value of ca. 2060 cm⁻¹ after exposure to acetylene. In the Pt sol/CO/H₂ systems, v(CO)_ads decreases to ca. 2050 cm⁻¹ after exposure to hydrogen gas. The lower frequency in the Pt sol/CO/H₂ system has been attributed to CO adsorption on more active metal sites formed from the reduction of surface platinum oxides. Exposure of the CO-treated platinum hydrosols to O₂ gas was found to cause the eventual disappearance of the v(CO)_ads band in infrared spectra, which was attributed to oxidation of adsorbed CO to CO₂ by weakly bound surface layers of platinum oxides formed by the oxygen treatment.     

Electroreduction of carbon dioxide: Part III. Adsorption and reduction of CO2 on platinum

The main properties of reductional adsorption of CO₂ on the platinum metals are studied. Chemisorbed particles are found to be produced only on platinum and rhodium. Electroreduction of CO₂ on these metals proceeds as a result of the interaction of CO₂ molecules activated in the course of adsorption on the metal surface with chemisorbed hydrogen. As a result, strongly chemisorbed particles are obtained on the surface which are the products of more profound reduction of CO₂ than to formic acid. The further reduction of these chemisorbed particles, accompanied by their desorption into the solution, is very slow due to very strong coupling of sorbed particles with the surface and to very fast backward adsorption of the reduction products. Neither reductional chemisorption of CO₂ nor interactions of CO₂ with adsorbed hydrogen were observed for iridium, palladium, osmium or ruthenium.     

A Highly Selective Copper–Indium Bimetallic Electrocatalyst for the Electrochemical Reduction of Aqueous CO2 to CO

The challenge in the electrochemical reduction of aqueous carbon dioxide is in designing a highly selective, energy‐efficient, and non‐precious‐metal electrocatalyst that minimizes the competitive reduction of proton to form hydrogen during aqueous CO₂ conversion. A non‐noble metal electrocatalyst based on a copper‐indium (Cu‐In) alloy that selectively converts CO₂ to CO with a low overpotential is reported. The electrochemical deposition of In on rough Cu surfaces led to Cu‐In alloy surfaces. DFT calculations showed that the In preferentially located on the edge sites rather than on the corner or flat sites and that the d‐electron nature of Cu remained almost intact, but adsorption properties of neighboring Cu was perturbed by the presence of In. This preparation of non‐noble metal alloy electrodes for the reduction of CO₂ provides guidelines for further improving electrocatalysis.     

Study of CO Dissociative Adsorption over Pt and Rh Catalysts by Inverse Gas Chromatography

Carbon monoxide dissociative adsorption was studied over silica-supported platinum, rhodium and Pt-Rh alloy catalysts, by Reversed Flow-Gas Chromatography. Using appropriate mathematical analysis physicochemical quantities such as fractional catalytic conversions of CO to CO₂, as well as rate constants for the adsorption, desorption and surface reaction, describing the dissociative adsorption of CO, were determined. From the variation of the above parameters against the nature of the studied catalysts (Rh content) useful conclusions concerning the mechanism of CO dissociative adsorption were extracted.     

Mechanistic Investigation of Alkali-Treated Photocatalytic CO2 Reduction: The Role of OH− and Metal Cations for Almost 100 % Selectivity of CO

In this work, the modulation of activity and selectivity via photoreduction of carbon dioxide under simulated sunlight was achieved by treating P25 and P25/Pt NPs with KOH. It found that KOH treatment could significantly improve the overall conversion efficiency and switch the selectivity for CO. Photoelectric characterizations and CO₂-TPD demonstrated that the synergistic effect of K⁺ and OH^- accelerated the separation and migration of photogenerated charges, and also improved CO₂ adsorption level. Significantly, the K ions could act as active sites for CO₂ adsorption and further activation. In situ FTIR measurements and DFT calculations confirmed that K⁺ enhanced the charge density of adjacent atoms and stabilize CO* groups, reducing the reaction energy barrier and inducing the switching of original CH₄ to CO, which played a selective regulatory role. This study provides insights into the photocatalytic activity and selectivity of alkali-treated photocatalysts and facilitates the design of efficient and product-specific photocatalysis.     

Electrode Potentials of Cells with an Electrolyte Based on Zirconium Dioxide in Gas Mixtures N2+ O2+ CO2+ CO: A Platinum Electrode

Steady-state potentials of various platinum electrodes are measured in cells containing electrolyte ZrO₂+ Y₂O₃(10 mol %) in the temperature range 673–773 K in binary equilibrium gas mixtures N₂+ O₂and CO + CO₂, as well as in four-component nonequilibrium gas mixtures N₂+ O₂+ CO₂+ CO containing 0–3 vol % CO and 0–10 vol % O₂. Adding CO to a gas mixture makes the electrode potential deviate from equilibrium, which is explained by chemisorption of CO on the electrode. The oxygen, which is adsorbed on platinum, interacts with CO; as a result, CO₂undergoes desorption and the surface concentration of CO drops.     

Enhancement of greenhouse gas adsorption on the new α-type reconstructed structure of two-dimensional borophene via biaxial strain engineering

The adsorption of CO, CO₂, and N₂O on a newly found α-type reconstructed form of borophene was investigated via density functional theory calculations. It is revealed that the new α-type reconstructed borophene structure consists of several large holes, and has the same order of stability as the predicted α₁-borophene in Wu et al. On the pristine reconstructed borophene case, CO and CO₂ adsorb moderately and weakly, respectively. Interestingly, N₂O spontaneously dissociated on the α-type reconstructed borophene. Upon the application of biaxial strain, especially at 10%, the adsorption of CO and CO₂ on the reconstructed borophene becomes significantly enhanced, and this is attributed to changes in the density of states near the Fermi level of the reconstructed borophene.     

Thermal desorption in catalytic systems 13. The surface adsorption of H2O,CO, and CO2 on copper oxide-zinc-aluminum-calcium catalysts for low-temperature conversion of carbon monoxide

Conclusions The relation between the thermodesorption parameters for Co, CO₂, and H₂O and the activity of copper oxide-zinc-aluminum-calcium catalysts has been discussed. It is suggested that high catalytic activity is associated with high CO, and low CO₂ and H₂O, adsorption on the nonuniform surface. The thermodesorption parameters are determined by the oxidation-reduction treatment to which the catalyst has been subjected.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2233–2238, October, 1978.For Communication 12, cf. [1].     

Electrochemical behavior of Pd–Rh alloys

Pd–Rh alloys were prepared by electrochemical codeposition. Bulk compositions of the alloys were determined by the energy dispersive X-ray analysis method, while surface compositions were determined from the potential of the surface oxide reduction peak. Cyclic voltammograms, recorded in 0.5 M H₂SO₄ for Pd–Rh alloys of different bulk and surface compositions, are intermediate between curves characteristic of Pd and Rh. The influence of potential cycling on electrochemical properties and surface morphologies of the alloys was studied. Due to electrochemical dissolution of metals, both alloy surface and bulk become enriched with Pd. Carbon oxides were adsorbed at a constant potential from the range of hydrogen adsorption. The presence of adsorbed CO₂ causes remarkable diminution of hydrogen adsorption but it does not significantly influence hydrogen insertion into the alloy bulk. On the other hand, in the presence of adsorbed CO, both hydrogen absorption and adsorption are strongly suppressed. Oxidative removal of the adsorbates results in a characteristic voltammetric peak, whose potential increases with the decrease in Rh surface content. Electron per site (eps) values calculated for the oxidation of the adsorbates change with alloy surface composition, more for CO₂ than CO adsorption, indicating the variation of the structure and composition of CO₂ and CO adsorption products. The course of the dependence of eps values on surface composition suggests that the products of CO₂ and CO adsorption on Pd–Rh alloys are similar but not totally identical.     

Exclusive Co-N4 Sites Confined in Two-dimensional Metal-Organic Layers Enabling Highly Selective CO2 Electroreduction at Industrial-Level Current

Metal-organic framework catalysts bring new opportunities for CO₂ electrocatalysis. Herein, we first conduct density-functional theory calculations and predict that Co-based porphyrin porous organic layers (Co-PPOLs) exhibit good activity for CO₂ conversion because of the low *CO adsorption energy at Co-N₄ sites, which facilitates *CO desorption and CO formation. Then, we prepare two-dimensional Co-PPOLs with exclusive Co-N₄ sites through a facile surfactant-assisted bottom-up method. The ultrathin feature ensures the exposure of catalytic centers. Together with large specific area, high electrical conductivity and CO₂ adsorption capability, Co-PPOLs achieve a peak faradaic efficiency for CO production (FE_CO=94.2 %) at a moderate potential in CO₂ electroreduction, accompanied with good stability. Moreover, Co-PPOLs reach an industrial-level current above 200 mA in a membrane electrode assembly reactor, and maintain near-unity CO selectivity (FE_CO>90 %) over 20 h in CO₂ electrolysis.     

Investigation into the adsorption of CO2, N2 and CH4 on kaolinite clay

Investigating the adsorption characteristics of CO₂, N₂ and CH₄ on kaolinite clay is beneficial for enhanced shale gas recovery by gas injection. In this paper, the experiments of CO₂, N₂ and CH₄ adsorption at 288 K, 308 K and 328 K on kaolinite clay were conducted, and the thermodynamics analysis of adsorption of three gases was performed. The findings reveal that the order of the uptakes of three gases on kaolinite clay is as follows: N₂ < CH₄ < CO₂. Reducing temperature enlarges the separation coefficients of CO₂ over CH₄ (α_CO2/CH4), CO₂ over N₂ (α_CO2/N2), and CH₄ over N₂ (α_CH4/N2). The value of α_CO2/CH4 greater than one validates that CO₂ is capable to directly replace the pre-adsorbed CH₄. The spontaneity of CO₂ adsorption is the highest, while N₂ has the lowest adsorption spontaneity. Injecting N₂ into gas-bearing reservoir can cause CH₄ desorption by lowering the spontaneity of CH₄ adsorption. Adsorbed CO₂ molecules form a most ordered rearrangement on kaolinite surface. The decrease rate of entropy loss for N₂ adsorption is higher than those for CO₂ and CH₄ adsorption.     

A complete experimental approach for synthesis gas separation studies using static gravimetric and column breakthrough experiments

In this work a combination of static gravimetric and inverse chromatographic techniques is used to study the adsorption and separation of the main synthesis gas components, i.e. CO₂, CO, CH₄ and H₂. The single component adsorption isotherms of CO₂, CO, CH₄ and H₂ on faujasite NaX were measured from 303 K to 473 K and over a large range of pressures (from 0 to 1200 kPa). Breakthrough curves of CO₂ and CO and their mixtures were determined at 323 K and 373 K and 100 kPa as an illustrative example. A nice agreement was noticed between the two above-mentioned techniques for single component adsorption. Binary mixture dynamics measurements were compared to the predictions of ideal adsorption solution theory (IAST) via the previously cited single component adsorption data.     

Harnessing Greenhouse Gases Absorption by Doped Fullerenes with Externally Oriented Electric Field

In this work, a theoretical investigation of the effects caused by the doping of C₂₀ with silicon (Si) atom as well as the adsorption of CO, CO₂ and N₂ gases to C₂₀ and C₁₉Si fullerenes was carried out. In concordance with previous studies, it was found that the choice of the doping site can control the structural, electronic, and energetic characteristics of the C₁₉Si system. The ability of C₂₀ and C₁₉Si to adsorb CO, CO₂ and N₂ gas molecules was evaluated. In order to modulate the process of adsorption of these chemical species to C₁₉Si, an externally oriented electric field was included in the theoretical calculations. It was observed that C₁₉Si is highly selective with respect to CO adsorption. Upon the increase of the electric field intensity the adsorption energy was magnified correspondingly and that the interaction between CO and C₁₉Si changes in nature from a physical adsorption to a partial covalent character interaction.     

Tailoring the Pore Size,Basicity, and Binding Energy of Mesoporous C3N5 for CO2 Capture and Conversion

We investigated the CO₂ adsorption and electrochemical conversion behavior of triazole-based C₃N₅ nanorods as a single matrix for consecutive CO₂ capture and conversion. The pore size, basicity, and binding energy were tailored to identify critical factors for consecutive CO₂ capture and conversion over carbon nitrides. Temperature-programmed desorption (TPD) analysis of CO₂ demonstrates that triazole-based C₃N₅ shows higher basicity and stronger CO₂ binding energy than g-C₃N₄. Triazole-based C₃N₅ nanorods with 6.1 nm mesopore channels exhibit better CO₂ adsorption than nanorods with 3.5 and 5.4 nm mesopore channels. C₃N₅ nanorods with wider mesopore channels are effective in increasing the current density as an electrocatalyst during the CO₂ reduction reaction. Triazole-based C₃N₅ nanorods with tailored pore sizes exhibit CO₂ adsorption abilities of 5.6–9.1 mmol/g at 0 °C and 30 bar. Their Faraday efficiencies for reducing CO₂ to CO are 14–38% at a potential of −0.8 V vs. RHE.     

Study on chemisorption of H<Subscript>2</Subscript>, O<Subscript>2</Subscript>, CO and C<Subscript>2</Subscript>H<Subscript>4</Subscript>on Pt-Ag/SiO<Subscript>2</Subscript>catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO₂catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H₂, O₂, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H₂and O₂adsorption that the addition of Ag to Pt/SiO₂leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO₂catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO₂. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemisorption of C₂H₄on Pt-Ag/SiO₂. The differential heat vs. uptake plots for C₂H₄adsorption on the oxygen-preadsorbed Pt/SiO₂and Pt-Ag/SiO₂catalysts suggest that the incorporation of Ag to Pt/SiO₂could decrease the ability for the oxidation of C₂H₄.     

Photo-induced carbon dioxide reduction on hexagonal tungsten oxide via an oxygen vacancies-involved process

Although converting the greenhouse gasses carbon dioxide (CO₂) into solar fuels is regarded as a convenient means of solar energy storage, the intrinsic mechanism on how the high chemical inertness linear CO₂ molecules is activated and converted on a semiconductor oxide is still elusive. Herein, by creating the oxygen vacancies on the typical hexagonal tungsten oxide (WO₃), we realize the continuous photo-induced CO₂ reduction to selectively produce CO under light irradiation, which was verified by isotope labeling experiment. Detailed oxygen vacancies evolution investigation indicates that light irradiation can simultaneously induce the in-situ formation of oxygen vacancies on hexagonal WO₃, and the oxygen vacancies promote the adsorption and activation of CO₂ molecules, leading to the CO₂ reduction to CO on the hexagonal WO₃ via an oxygen vacancies-involved process. Besides, the existence of water further promotes the formation of CO₂ reduction intermediate, further promote the CO₂ photoreduction. Our work provides insight on the mechanism for converting CO₂ into CO under light irradiation.     

Dissociative adsorption of molecular hydrogen onto Pt<Subscript>6</Subscript> and Pt<Subscript>19</Subscript> platinum clusters located on the tin dioxide surface: Quantum-chemical modeling

It is suggested that, for the operation of platinum catalysts based on tin dioxide in air hydrogen fuel cells, hydrogen spillover (migration) leading to a change in the electron and proton contributions of the catalyst conductivity is of crucial importance. The hydrogen adsorption, dissociation, and migration in the platinum-tin dioxide-hydrogen system surface have been modeled by the density functional theory method within the generalized gradient approximation (GGA) under periodic conditions using a projector-augmented plane-wave (PAW) basis set with a pseudopotential. It has been demonstrated that the adsorption energy of a hydrogen molecule onto a platinum cluster increases from 1.6 to 2.4 eV as the distance to the SnO₂ substrate decreases. The calculated Pt-H bond length for adsorbed structures is 1.58–1.78 Å. The computer modeling has demonstrated that: (1) the hydrogen adsorption energy on clusters is higher than on the perfect platinum surface; (2) dissociative chemisorption onto Pt _n clusters can occur without a barrier and depends on the adsorption site and the cluster structure; (3) the adsorption energy of hydrogen onto the SnO₂ surface is higher than the adsorption energy onto the platinum cluster surface: (4) multiple H₂ dissociation on the tin dioxide surface occurs with a barrier; (5) the dissociation adsorption of hydrogen molecules onto the platinum cluster surface followed by atom migration (spillover) is energetically favorable.     

A Doping Technique that Suppresses Undesirable H2 Evolution Derived from Overall Water Splitting in the Highly Selective Photocatalytic Conversion of CO2 in and by Water

Photocatalytic conversion of CO₂ to reduction products, such as CO, HCOOH, HCHO, CH₃OH, and CH₄, is one of the most attractive propositions for producing green energy by artificial photosynthesis. Herein, we found that Ga₂O₃ photocatalysts exhibit high conversion of CO₂. Doping of Zn species into Ga₂O₃ suppresses the H₂ evolution derived from overall water splitting and, consequently, Zn‐doped, Ag‐modified Ga₂O₃ exhibits higher selectivity toward CO evolution than bare, Ag‐modified Ga₂O₃. We observed stoichiometric amounts of evolved O₂ together with CO. Mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species on the photocatalyst surface, but the CO₂ introduced in the gas phase. Doping of the photocatalyst with Zn is expected to ease the adsorption of CO₂ on the catalyst surface.     

Mechanism of CO oxidation in excess H2 over CuO/CeO2 catalysts: ESR and TPD studies

The oxidation of CO with oxygen over (0.25–6.4)% CuO/CeO₂ catalysts in excess H₂ is studied. CO conversion increases and the temperature range of the reaction decreases by 100 K as the CuO content is raised. The maximal CO conversion, 98.5%, is achieved on 6.4% CuO/CeO₂ at 150°C. At T > 150°C, the CO conversion decreases as a result of the deactivation of part of the active sites because of the dissociative adsorption of hydrogen. CO is efficiently adsorbed on the oxidized catalyst to form CO-Cu⁺ carbonyls on Cu₂O clusters and is oxidized by the oxygen of these clusters, whereas it is neither adsorbed nor oxidized on Cu⁰ of the reduced catalysts. The activity of the catalysts is recovered after the dissociative adsorption of O₂ on Cu⁰ at T ～ 150°C. The activation energies of CO, CO₂, and H₂O desorption are estimated, and the activation energy of CO adsorption yielding CO-Cu⁺ carbonyls is calculated in the framework of the Langmuir-Hinshelwood model.