CO Coverage Research Articles

Morphology control of metal-modified zirconium phosphate support structures for the oxygen evolution reaction.

The electrochemical oxygen evolution reaction (OER) is the half-cell reaction for many clean-energy production technologies, including water electrolyzers and metal-air batteries. However, its sluggish kinetics hinders the performance of those technologies, impeding them from broader implementation. Recently, we reported the use of zirconium phosphate (ZrP) as a support for transition metal catalysts for the oxygen evolution reaction (OER). These catalysts achieve promising overpotentials with high mass activities. Herein, we synthesize ZrP structures with controlled morphology: hexagonal platelets, rods, cubes, and spheres, and subsequently modify them with Co(ii) and Ni(ii) cations to assess their electrochemcial OER behavior. Through inductively coupled plasma mass-spectrometry measurements, the maximum ion exchange capacity is found to vary based on the morphology of the ZrP structure and cation selection. Trends in geometric current density and mass activity as a function of cation selection are discussed. We find that the loading and coverage of cobalt and nickel species on the ZrP supports are key factors that control OER performance.

Theoretical insights into the effect of the overpotential on CO electroreduction mechanisms on Cu(111): regulation and application of electrode potentials from a CO coverage-dependent electrochemical model.

A recently proposed CO coverage-dependent electrochemical model combined with the calculation of electronic structure is applied for the first time to study the effect of the overpotential on Cu-catalyzed CO electroreduction mechanisms by changing the coverage of surface adsorbed CO. The results show that the presently defined CH2O and CHOH pathways may be able to occur parallelly under different overpotentials. However, high overpotentials will facilitate CO electroreduction, thus explaining why a high overpotential is required during CO2 electroreduction in experiments on Cu electrodes. The potential-limiting step may be further CO electroreduction into CHO, which is considered as the origin of the experimentally observed high overpotentials. The analyses of electronic structure show that an adsorbed COδ- species is formed on the Cu electrodes, validating the previous experimental speculations on electron transfer between CO and Cu electrodes. More and more electrons are transferred into the π antibonding orbitals of the adsorbed CO with increasing surface CO coverage, leading to increasing overpotential and weaker and weaker CO bonding with the Cu surface. Thus, the significantly lower barrier of further CO electroreduction at higher overpotential can be correlated with lower CO adsorption energy. Interestingly, it is found that there is greater localization of electrons around the C than the O atom in the adsorbed CO molecule, explaining why the hydrated proton prefers to reach the C atom to form intermediate CHO rather than COH.

Monitoring of CO Binding Sites on Stepped Pt Single Crystal Electrodes in Alkaline Solutions by in Situ FTIR Spectroscopy.

The site geometry preference of CO binding on stepped Pt single crystals in alkaline solution was investigated by in situ FTIR spectroscopy. The surfaces of the Pt single crystals consisted of different width (111) terraces, interrupted by (110) or (100) monatomic steps. Experiments carried out with CO adsorbed exclusively on the top of the steps revealed that only linearly bonded CO formed on the (110) steps, while two CO binding geometries (linear and bridge) were observed on the (100) steps. On one hand, for CO adsorbed only on the steps, the positions of the bands corresponding to linearly bonded CO were similar, regardless of the density of steps, suggesting the existence of an interaction between COads only along the line of the steps. On the other hand, for full CO coverage, the CO stretching frequencies and the geometry of bound CO were sensitive to the width of the (111) terraces and the step orientations. Consequently, the CO binding sites favored linearly bonded CO for surfaces consisting of shorter (111) terraces and (110) steps. Bridge-bonded CO was favored on surfaces consisting of shorter (111) terraces interrupted by (100) steps. In order to understand the origin of the preference of CO binding sites, the results were compared to the corresponding behavior in acid media, which revealed that, in addition to the effect inherent to the Pt surface, the charge on the metal side in an aqueous environment should be taken into consideration. The analysis suggested that the CO adlayers formed at full coverage in acidic and alkaline media had different structures. On the other hand, the structure of the layer of CO adsorbed only at the steps was independent of pH.

Performance evaluation of μDMFCs based on porous-silicon electrodes and methanol modification

This study aims to develop micro direct methanol fuel cells (μDMFCs) incorporating flow-field plates with porous-silicon diffusion layers to form two types of bipolar electrodes, one with a hill-like structure (HLS) and the other with a through-hole silicon (THS) structure. Carbon nanotubes are grown on the surface diffusion layers to serve as catalyst supports. Furthermore, methanol fuel is modified by adding SDSS surfactant with the intent of enhancing its wettability and ability of CO2 removal for preventing CO2 coverage of catalyst layer. The experimental results indicate that the maximum power density of this HLS-THS cell (0.186 mW/cm2) is 4.4 times higher than that of the cell with conventional CP-CP (carbon paper) electrodes. The μDMFCs without SDSS has the highest output voltage at 0.66 V, yet the value linearly decreases to 0 V in only 5.5 h. The μDMFCs with 0.1% SDSS can maintain an average output voltage of 0.45 V for 8 h before the value decreases to approximately 0 V as a result of fuel depletion. Although the output voltage of the μDMFCs with 0.5% SDSS remains steadily at 0.425 V, the voltage decreases to negative values after 7 h because of fuel depletion and crossover.

Constraining CO coverage on copper promotes high-efficiency ethylene electroproduction

The availability of inexpensive industrial CO gas streams motivates efficient electrocatalytic upgrading of CO to higher-value feedstocks such as ethylene. However, the electrosynthesis of ethylene by the CO reduction reaction (CORR) has suffered from low selectivity and energy efficiency. Here we find that the recent strategy of increasing performance through use of highly alkaline electrolyte—which is very effective in CO2RR—fails in CORR and drives the reaction to acetate. We then observe that ethylene selectivity increases when we constrain (decrease) CO availability. Using density functional theory, we show how CO coverage on copper influences the reaction pathways of ethylene versus oxygenate: lower CO coverage stabilizes the ethylene-relevant intermediates whereas higher CO coverage favours oxygenate formation. We then control local CO availability experimentally by tuning the CO concentration and reaction rate; we achieve ethylene Faradaic efficiencies of 72% and a partial current density of >800 mA cm−2. The overall system provides a half-cell energy efficiency of 44% for ethylene production. The electrocatalytic upgrading of CO to higher-value feedstocks provides a promising route to multicarbon products. Here, the authors show that high ethylene selectivity can be achieved by constraining CO availability on copper, with an ethylene Faradaic efficiency of 72% and a partial current density of >800 mA cm−2.

Growth of cobalt films at room temperature using sequential exposures of cobalt tricarbonyl nitrosyl and low energy electrons

Cobalt thin films were grown at room temperature using sequential exposures of cobalt tricarbonyl nitrosyl (CTN, Co(CO)3NO) and low energy (75–175 eV) electrons. During this cyclic growth process, the CTN molecules were first adsorbed on the substrate. The electrons then induced the desorption of the carbonyl and nitrosyl ligands from the adsorbed CTN. The removal of CO and NO ligands produced new adsorption sites. Subsequent CTN exposures allowed CTN to react with these new adsorption sites on the substrate. In situ ellipsometry was utilized to monitor the film thickness during the electron enhanced growth. Co growth rates as high as 1.3 Å/cycle were observed by in situ ellipsometry depending on the reaction conditions. The in situ ellipsometry also observed the CTN adsorption and the removal of the carbonyl and nitrosyl ligands. Quadrupole mass spectrometer measurements confirmed the desorption of CO and NO during electron exposures. X-ray photoelectron spectroscopy (XPS) measured N XPS signals from the Co films deposited using electron exposures at 200 eV. The N/Co XPS signal ratio was consistent with the dissociation of 13% of the nitrosyl ligands on the CTN precursors that lead to Co deposition. In contrast, the negligible C XPS signals from the Co films indicated that the CO ligands were desorbed completely from CTN by the electron exposures at 200 eV. Under identical reaction conditions at lower incident electron currents, the maximum growth rate was obtained at an electron energy of 125 eV. Because the Co growth depends on the electron flux, the Co films were deposited only on the surface area irradiated by the electron beam. The spatial profile of the Co film deposited using long electron exposure times was mapped by ex situ spectroscopic ellipsometry. This spatial profile displayed a pronounced flat top that was consistent with the electron flux desorbing nearly all the CO and NO surface coverage in the central area of the electron beam during each reaction cycle. The spatial profile was used to calculate an electron induced desorption cross section of σ = 2 × 10−17 cm2 at 200 eV. This cross section was in approximate agreement with the cross sections for the electron impact dissociation of CTN in the gas phase.

Mesoporous carbon supported MgO for CO2 capture and separation of CO2/N2

Mesoporous carbon derived from pongamia pinnata fruit hulls was used as support to incorporate magnesium oxide for the study of CO2 adsorption and separation of CO2/N2. All synthesized adsorbents were characterized by PXRD, N2 adsorption-desorption isotherms, Raman and SEM with EDX techniques. Characterization results revealed the existence of magnesium oxide on mesoporous carbon. CO2 adsorption on MgO incorporated mesoporous carbon was higher than bulk mesoporous carbon, due to the electrostatic interaction between magnesium oxide and CO2. High CO2 adsorption capacity 1.68 mmol/g was obtained for 10 wt% MgO incorporated mesoporous carbon at 298 K, 1 bar compared to remaining loadings, because of the high content of MgO. However, the N2 adsorption capacity decreased with the increase of MgO content due to a decrease in surface area and no interaction of the N2 molecule with the adsorbent. The selectivity of CO2/N2 was higher on 10 wt% MgO incorporated mesoporous carbon and the value was 40. The heat of CO2 adsorption was 36KJ/mol at low coverage of CO2, and CO2 adsorption capacity was constant in each adsorption cycle over the same adsorbent.

Facile Fischer–Tropsch Chain Growth from CH2 Monomers Enabled by the Dynamic CO Adlayer

Numerous chain growth mechanisms, namely CO insertion and carbide, and active sites (flat and stepped surfaces) have been proposed to explain how hydrocarbons are formed from syngas during the Fischer–Tropsch reaction on Ru catalysts, particularly active and selective toward long-chain products. While these reaction pathways are supported by density functional theory (DFT) calculations, computational models often considered surfaces at rather low adsorbate coverage. A systematic comparison of chain growth mechanisms including the CO adlayer present on the catalyst’s surface under reaction conditions is therefore not available due to the challenging representation of co-adsorbate interactions in DFT models. Here, we show that the high coverage of chemisorbed CO on the metal surface favors the carbide mechanism on flat surfaces according to ab initio molecular dynamics simulations, which introduce the complex adlayer effects at the reaction temperature of 200 °C. At the considered CO and H coverages (0.50–0.72 and 0.24 monolayer, respectively) hydrocarbon formation involves CH2 monomers yielding ethylene and propylene as primary products, consistent with the selectivity observed in experiments. Such mechanism is favored by the presence of the CO adlayer. Indeed, in the absence of co-adsorbed CO, methane may be formed on the flat surface and the first C–C bond occurs preferentially on stepped surfaces via CH and CH2 monomers with a higher free-energy barrier (55 kJ mol–1) compared to the coupling of two CH2 species at high CO coverage on the flat surface (20 kJ mol–1). Therefore, the CO adlayer strongly modulates the nature of chain growth monomers and active sites and drives the formation of hydrocarbons during Ru-catalyzed Fischer–Tropsch. Overall, these results show how adsorbate–adsorbate interactions dictate reaction mechanisms operating in adlayers, ubiquitous in heterogeneous catalysis.

The effect of CO on CO2 methanation over Ru/Al2O3 catalysts: a combined steady-state reactivity and transient DRIFT spectroscopy study

The reactivity of Ru/Al2O3 catalysts in the hydrogenation of CO/CO2 gas stream is investigated in this work to assess the possibility of carrying out CO2 methanation even in the presence of CO in the feed stream. Such a goal is pursued by conducting reactivity studies at process conditions of industrial interest (i.e., at high COx per-pass conversion and with concentrated COx/H2 streams) and by monitoring the surface species on the catalyst through transient DRIFTS-MS analysis. The catalyst shows gradual deactivation when the methanation is carried out in the presence of CO in the gas feed at low temperatures (200–300 °C). However, stable performance is observed at higher temperatures, showing CH4 yields even higher than those observed during methanation of a pure CO2 feed. DRIFTS-MS experiments agree with a CO2 methanation pathway where CO2 is adsorbed as bicarbonate on Al2O3 and successively hydrogenated to methane on Ru, passing through formate and carbonyl intermediates. In the presence of CO at low temperature, the catalyst shows a higher CO coverage of the Ru sites, a larger formate coverage of the alumina sites and the presence of adsorbed carbonaceous species, identified as carboxylate and hydrocarbon species. By carrying out the CO2 hydrogenation on the deactivated catalyst, carboxylates remain on the surface, effectively blocking CO2 adsorption sites. However, the catalyst deactivation at low temperature is reversible as thermal treatment (>350 °C) is able to restore the catalytic activity. Notably, working above the carboxylate decomposition temperature ensures a clean catalyst surface without high CO coverage, resulting in stable and high performance in CO/CO2 methanation.

Electronic Effects Determine the Selectivity of Planar Au-Cu Bimetallic Thin Films for Electrochemical CO2 Reduction.

Au–Cu bimetallic thin films with controlled composition were fabricated by magnetron sputtering co-deposition, and their performance for the electrocatalytic reduction of CO2 was investigated. The uniform planar morphology served as a platform to evaluate the electronic effect isolated from morphological effects while minimizing geometric contributions. The catalytic selectivity and activity of Au–Cu alloys was found to be correlated with the variation of electronic structure that was varied with tunable composition. Notably, the d-band center gradually shifted away from the Fermi level with increasing Au atomic ratio, leading to a weakened binding energy of *CO, which is consistent with low CO coverage observed in CO stripping experiments. The decrease in the *CO binding strength results in the enhanced catalytic activity for CO formation with the increase in Au content. In addition, it was observed that copper oxide/hydroxide species are less stable on Au–Cu surfaces compared to those on the pure Cu surface, where the surface oxophilicity could be critical to tuning the binding strength of *OCHO. These results imply that the altered electronic structure could explain the decreased formation of HCOO– on the Au–Cu alloys. In general, the formation of CO and HCOO– as main CO2 reduction products on planar Au–Cu alloys followed the shift of the d-band center, which indicates that the electronic effect is the major governing factor for the electrocatalytic activity of CO2 reduction on Au–Cu bimetallic thin films.

Combined spatially resolved operando spectroscopy: New insights into kinetic oscillations of CO oxidation on Pd/γ-Al2O3

Spatially resolved, combined energy dispersive EXAFS (EDE) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements have been performed over a fixed catalyst bed of Pd/γ-Al2O3 during kinetic oscillations of CO oxidation. The kinetic oscillations of CO oxidation over Pd (or for that matter Pt or Rh) catalysts are a complicated phenomenon that require characterisation techniques with high time resolution and spatial resolution in order to make links between catalyst structure and surface reactivity. By measuring the extent of Pd oxidation at the nanoparticle surface, from Pd K-edge EDE, and matching this with the CO coverage, from DRIFTS spectra, at multiple positions of the fixed bed reactor it is found that the majority of the catalyst undergoes a sharp transition from the CO poisoned catalyst to the highly active, oxidised Pd surface. This transition occurs initially at the end of the catalyst bed, nearest the outlet, and propagates upstream with increasing temperature of the reactor. The oscillations in Pd surface oxide formation and CO coverage are observed only in the first ∼1 mm of the bed, which gives rise to oscillations in CO2 and O2 concentrations observed by end-pipe mass spectrometry after the light-off temperature. The catalyst initially exists as less active, CO poisoned metallic Pd nanoparticles before light-off which transition to a highly active state after light-off when the Pd nanoparticle surface becomes dominated by chemisorbed oxygen. Kinetic oscillations only occur at the front of the catalyst bed where there is sufficient concentration of CO in the gas phase to compete with O2 for adsorption sites at the catalyst surface. We demonstrate the complex nature of the evolving catalyst structure and surface reactivity during catalytic operation and the need for spatially resolved operando methods for understanding and optimising catalyst technologies.

Diffusion mechanisms of metal atoms in Pd[sbnd]Au bimetallic catalyst under CO atmosphere based on ab initio molecular dynamics

Reconstruction of heterogeneous catalysts during reaction, especially caused by the adsorption of reactants, is highly important for the structural evolution of nanoparticles (NPs) during activation and reaction processes. In this work, for the first time the CO-induced dynamic structure of Pd@Au core-shell NPs with different size and shape has been studied systemically using ab initio molecular dynamics. Our calculation has demonstrated that the thermostability of Pd@Au bimetallic NPs is decreased with increasing CO coverage. However, the kinetic stability can be enhanced when CO coverage is very high. With the adsorption of CO, the interaction between surface unoccupied atoms and nearby metal atoms at the second layer is strengthened, while the stress distribution in the second layer is significantly changed. The surface unoccupied metal atoms then migrate into the second layer, and metal atoms in the second layer move to surface in return. Such atomic diffusion between the top two layers leads to the atomic exchange in NPs interior layer by layer. Finally, Pd and Au atoms are redistributed in NPs, and Pd atoms accumulate at surface because of stronger CO adsorption. In a word, the segregation is dominated by the inward diffusion of surface unoccupied metal atoms. The great challenge in this work is how to establish the relationship between gas atmosphere and NP kinetic stability for determining the dynamic 3D bimetallic NPs.

Carbon Monoxide Mediated Hydrogen Release from PtCu Single-Atom Alloys: The Punctured Molecular Cork Effect

Pt-based materials are used extensively in heterogeneous catalytic processes, but they are notoriously susceptible to poisoning by CO. In contrast, highly dilute binary alloys formed of isolated Pt atoms in a Cu metal host, known as PtCu single-atom alloys (SAAs), are more resilient to CO poisoning during catalytic hydrogenation reactions. In this article, we describe how CO affects the adsorption and desorption of H2 from a model PtCu(111) SAA surface and gain a microscopic understanding of these species’ interaction at the Pt atom active sites. By combining temperature-programmed desorption and scanning tunneling microscopy with first-principles kinetic Monte Carlo, we identify CO as a Pt site blocker that prevents the low temperature adsorption and desorption of H2, the so-called molecular cork effect, first realized when examining PdCu SAAs. Intriguingly, for the case of PtCu, H2 desorption occurs before CO release is detected. Furthermore, desorption experiments show a nonlinear relationship between CO coverage of the Pt sites and H2 desorption peak temperature. When all the Pt atoms are saturated by CO, a very sharp H2 desorption feature is observed 55 K above the regular desorption temperature of H2. Our simulations reveal that the origin of these effects is the fact that desorption of just one CO molecule from a Pt site facilitates the fast release of many molecules of H2. In fact, just 0.7% of the CO adsorbed at Pt sites has desorbed when the H2 desorption peak maximum is reached. The release of H2 from CO-corked PtCu SAA surfaces is analogous to the escape of gas from a pressurized container with a small puncture. Given that small changes in CO surface coverage lead to large changes in H2 evolution energetics, the punctured molecular cork effect must be considered when modeling reaction mechanisms on similar alloy systems.

Suppressing H2 Evolution and Promoting Selective CO2 Electroreduction to CO at Low Overpotentials by Alloying Au with Pd

CO 2 electroreduction is a promising technology to produce chemicals and fuels from renewable resources. Polycrystalline and nanostructured metals have been tested extensively while less effort has been spent on understanding the performance of bimetallic alloys. In this work, we study compositionally variant, smooth Au-Pd thin film alloys to discard any morphological or mesoscopic effect on the electrocatalytic performance. We find that the onset potential of CO formation exhibits a strong dependence on the Pd content of the alloys. Strikingly, palladium, a hydrogen evolution catalyst with reasonable exchange current density, suppresses hydrogen evolution when alloyed with gold in the presence of CO 2 . Cyclic voltammetry, in situ surface enhanced infrared absorption spectroscopy, and potential-dependent online product analysis strongly suggest that by alloying Au with Pd a significant increase in the surface coverage of adsorbed CO occurs with increasing Pd content at low overpotentials (e.g., approximately -0.35 V vs RHE). Such an increase in CO coverage suppresses H 2 evolution due to the lack of vacant active sites. Moreover, the overall increase in the binding energy with the CO 2 intermediates gained with the addition of Pd increases the CO production at low overpotentials, where polycrystalline Au suffers from poor CO 2 adsorption and poor selectivity for CO production. These results show that promising CO 2 reduction electrode materials (e.g., Au) can be alloyed not only to tune the catalyst's activity but also to deliberately decrease the availability of surface sites for competitive H 2 evolution.

Temperature-Controlled CO Adsorption Configurations on (2 × 1)Ni–O/Ni(110) Surfaces

CO adsorptions and configuration evolutions with temperatures on (2 × 1)Ni–O row structures on Ni(110) surfaces were studied by using ultrahigh vacuum–Fourier transform infrared spectroscopy, thermal desorption spectroscopy, and density functional theory calculations. Two kinds of adsorption configurations were identified. In the top configuration at low temperature (90 K), the carbon atom of one CO binds to one Ni atom in the Ni–O rows with a tilt angle of about 53°, and the vibration frequency of CO is 2100–2119 cm–1 depending on CO coverage. In the bridge configuration near room temperature (280 K), the carbon atom of one CO binds to two Ni atoms from the neighboring Ni–O rows, and the vibration frequency is 2030–2039 cm–1. By annealing the sample prepared at 90 to 280 K, the top adsorption configuration gradually evolves into the ordered bridge adsorption configuration via a disordered state. In the disordered state, the top and bridge configurations are distributed in disorder, induce strong transver...

Morphology and Reactivity Evolution of HCP and FCC Ru Nanoparticles under CO Atmosphere

The morphology change of metallic nanoparticles induced by the interaction of gas molecules with nanoparticles is a very important surface chemistry process in heterogeneous catalysis. Here, we performed a thorough study to provide understanding of the influence of CO adsorption on theoretically established Ru nanoparticle models through an approach combining density functional theory, Wulff construction, and ab initio atomistic thermodynamics. The morphology of constructed Ru nanoparticles undergoes significant evolution upon changing CO coverage, exposed temperature, and pressure. The contribution from flat facets becomes more significant in equilibrium morphology of nanoparticles as the surface CO coverage increases. Such morphological evolution has a consequential impact on the inherited catalytic performance of Ru NPs, as they were applied into three probe catalytic reactions, CO direct dissociation, HCO formation, and CH3 hydrogenation. This study enriches the current knowledge of the ruthenium nano...

Amorphous, Periodic Model of a Copper Electrocatalyst with Subsurface Oxygen for Enhanced CO Coverage and Dimerization

Oxide-derived copper electrocatalysts have been found to possess excellent selectivity toward the production of multicarbon products from CO2. The presence of subsurface oxygen in these catalysts has been confirmed experimentally, but the resulting amorphous structure has yet to be captured by theoretical models. In this study, the role of subsurface oxygen atoms is investigated with density functional theory, using a disordered oxide-derived Cu surface model (d-ODCu). The presence of subsurface oxygen atoms increases the maximum adsorption coverage of the important CO intermediate but decreases that of H atoms because of electronic and geometric effects. However, this has no significant influence on the free-energy activation barrier or endothermicity of the CO-dimerization reaction step, allegedly the key to multicarbon product formation.

PH effects on the electrochemical reduction of CO(2) towards C2 products on stepped copper

We present a microkinetic model for CO(2) reduction (CO(2)R) on Cu(211) towards C2 products, based on energetics estimated from an explicit solvent model. We show that the differences in both Tafel slopes and pH dependence for C1 vs C2 activity arise from differences in their multi-step mechanisms. We find the depletion in C2 products observed at high overpotential and high pH to arise from the 2nd order dependence of C-C coupling on CO coverage, which decreases due to competition from the C1 pathway. We further demonstrate that CO(2) reduction at a fixed pH yield similar activities, due to the facile kinetics for CO2 reduction to CO on Cu, which suggests C2 products to be favored for CO2R under alkaline conditions. The mechanistic insights of this work elucidate how reaction conditions can lead to significant enhancements in selectivity and activity towards higher value C2 products.

Modeling the effect of surface CO coverage on the electrocatalytic reduction of CO2 to CO on Pd surfaces.

Electrocatalytic reduction of CO2 has attracted considerable attention recently, and it was found experimentally that Pd could show activity for the electroreduction of CO2 to CO. However, theoretical studies showed that the adsorption of CO on Pd surfaces is strong and the coverage of CO is high, indicating that the interactions between the neighboring adsorbed CO and other reaction intermediates on the Pd surfaces cannot be neglected. Here, with density functional theory calculations and utilizing the Sabatier analysis method, we find that an adsorbate-adsorbate interaction is playing a crucial role in the modeling of the electrocatalytic reduction of CO2 to CO on Pd surfaces, whilst the reaction rates obtained by neglecting the interactions between the surface adsorbates are substantially lower than those reported in the experiments. Upon analyzing the interactions quantitatively and using a self-consistent iterative microkinetic modeling method, we find that the active site for CO2 electroreduction is Pd(111) at different potentials applied. Our modeling results provide a reasonable computational interpretation for the electroreduction of CO2 to CO on Pd.

Acetaldehyde polymerization on Co(0001): the role of CO.

The adsorption and polymerization of acetaldehyde (CH3CHO) have been investigated on clean and CO pre-covered Co(0001) surfaces using the temperature programmed desorption (TPD) method. On the clean Co(0001) surface, CH3CHO molecules can polymerize to produce paraldehyde with very low efficiency. With pre-dosed CO molecules on Co(0001), the decomposition of CH3CHO is greatly inhibited. When the coverage of pre-dosed CO is <0.33 ML, no enhancement of CH3CHO polymerization is observed. However, when the pre-dosed CO coverage is >0.33 ML, the polymerization of CH3CHO is significantly enhanced during the TPD process. Further results suggest that CO molecules adsorbed at the bridge/hollow sites may initialize the polymerization by nucleophilic attack of CH3CHO molecules with their O atoms. Moreover, the polymerization product induced by CO molecules is not paraldehyde, but linear polymer chains of CH3CHO at low CH3CHO coverages and probably three dimensional polymer structures at high CH3CHO coverages.