H_2-induced CO adsorption and dissociation over Co/Al_2O_3 catalyst

The activation of adsorbed CO is an important step in CO hydrogenation. The results from TPSR of pre-adsorbed CO with H2 and syngas suggested that the presence of H2 increased the amount of CO adsorption and accelerated CO dissociation. The H2 was adsorbed first, and activated to form H＊ over metal sites, then reacted with carbonaceous species. The oxygen species for CO2 formation in the presence of hydrogen was mostly OH^＊, which reacted with adsorbed CO subsequently via CO^＊＋OH^＊ → CO2^＊＋H^＊; however, the direct CO dissociation was not excluded in CO hydrogenation. The dissociation of C-O bond in the presence of H2 proceeded by a concerted mechanism, which assisted the Boudourd reaction of adsorbed CO on the surface via CO^＊＋2H^＊ → CH^＊＋OH^＊. The formation of the surface species （CH） from adsorbed CO proceeded as indicated with the participation of surface hydrogen, was favored in the initial step of the Fischer-Tropsch synthesis.

CO adsorption on a Pt(111) surface partially covered with FeO_x nanostructures

The adsorption of CO on Pt group metals, as a most fundamental elementary reaction step, has been widely studied in catalysis and electrocatalysis. Particularly, the structures of CO on Pt(111) have been extensively investigated, owing to its importance to both fundamental and applied catalysis. Yet, much less is known regarding CO adsorption on a Pt(111) surface modulated by supported oxide nanostructures,which is of more relevance to technical catalysis. We thus investigated the coverage-dependent adsorption of CO on a Pt(111) surface partially covered by Fe Oxnanostructures, which has been demonstrated as a remarkable catalyst for low-temperature CO oxidation. We found that, due to its strong chemisorption, the coverage-dependent structure of CO on bare Pt is not influenced by the presence of Fe Ox. But,oxygen-terminated Fe Oxnanostructures could modulate the diffusivity of CO at their vicinity, and thus affect the formation of ordered CO superstructures at low temperatures. Using scanning tunneling microscopy(STM), we inspected the diffusivity of CO, followed the phase transitions of CO domains, and resolved the molecular details of the coverage-dependent CO structures. Our results provide a full picture for CO adsorption on a Pt(111) surface modulated by oxide nanostructures and shed lights on the inter-adsorbate interaction on metal surfaces.

Convergence Issues Associated with Cutoff Energies and Ab Initio Studies of Adsorption of CO on W and Pt

The experimental research programs of 1950s, to understand the adsorption of CO on W surfaces, changed to ab initio studies in 2000s. The goals were to seek improved practical applications. Most of the studies were based on density functional theory. Many studies also used programs, such as VASP (Vienna Abinitio simulation package) and CPMD. The computational procedures used plane wave approximations. This needed studies with selection of K points and cutoff energy selection to assure convergence in energy calculations. Observations and analysis of papers published from 2006 to 2022 indicate that the cutoff energies were selected arbitrarily without any needed convergence studies. By selecting a published 2006 paper, this paper has clearly showed that an arbitrary selection of cutoff energy, such as 460 eV, is not in the range of, cutoff energies that assure convergence of energy calculations, with ab initio methods and have indicated correction procedures. .

Regulated CO adsorption by the electrode with OH^(-) repulsive property for enhancing C–C coupling

Electrochemical CO_(2) reduction driven by renewable electricity is one of the promising strategies to store sus-tainable energy as fuels.However,the selectivity of value-added multi-carbon products remains poor for further application of this process.Here,we regulate CO adsorption by forming a Nafion layer on the copper(Cu)electrode that is repulsive to OH^(-),contributing to enhanced selectivity of CO_(2) reduction to C_(2) products with the suppression of C 1 products.The operando Raman spectroscopy indicates that the local OH^(-)would adsorb on part of active sites and decrease the adsorption of CO.Therefore,the electrode with repulsive to OH^(-)can adjust the concentration of OH^(-),leading to the increased adsorption of CO and enhanced C–C coupling.This work shows that electrode design could be an effective strategy for improving the selectivity of CO_(2) reduction to multi-carbon products.

Controllable CO adsorption determines ethylene and methane productions from CO_(2) electroreduction

Among all CO2 electroreduction products,methane(CH4)and ethylene(C_(2)H_(4))are two typical and valuable hydrocarbon products which are formed in two different pathways:hydrogenation and dimerization reactions of the same CO intermediate.Theoretical studies show that the adsorption configurations of CO intermediate determine the reaction pathways towards CH4/C_(2)H_(4).However,it is challenging to experimentally control the CO adsorption configurations at the catalyst surface,and thus the hydrocarbon selectivity is still limited.Herein,we seek to synthesize two well-defined copper nanocatalysts with controllable surface structures.The two model catalysts exhibit a high hydrocarbon selectivity toward either CH4(83%)or C_(2)H_(4)(93%)under identical reduction conditions.Scanning transmission electron microscopy and X-ray absorption spectroscopy characterizations reveal the low-coordination Cu^(0)sites and local Cu^(0)/Cu^(+)sites of the two catalysts,respectively.CO-temperature programed desorption,in-situ attenuated total reflection Fourier transform infrared spectroscopy and density functional theory studies unveil that the bridge-adsorbed CO(CO_(B))on the low-coordination Cu^(0)sites is apt to be hydrogenated to CH4,whereas the bridge-adsorbed CO plus linear-adsorbed CO(CO_(B)+CO_(L))on the local Cu^(0)/Cu^(+)sites are apt to be coupled to C_(2)H_(4).Our findings pave a new way to design catalysts with controllable CO adsorption configurations for high hydrocarbon product selectivity.

Large adsorption energies for CO on Sc_n(n=2-8,13) nanoclusters

In order to seek a transition metal cluster with high ability to adsorb CO molecule, the author performs a density function theory calculation on COScn （n = 2-8, 13） clusters. The results demonstrate that COScn （n = 2-8, 13） clusters have the large adsorption energies of which the values are over 3.6 eV, and the elongations of C-O bond length exceed 20% in most calculated sizes. Adsorbing CO contributes to the improvement of the chemical activity, but reduces the magnetic moment of corresponding Scn cluster.

Accelerated prediction of Cu-based single-atom alloy catalysts for CO_(2) reduction by machine learning

Various strategies,including controls of morphology,oxidation state,defect,and doping,have been developed to improve the performance of Cu-based catalysts for CO_(2) reduction reaction(CO_(2)RR),generating a large amount of data.However,a unified understanding of underlying mechanism for further optimization is still lacking.In this work,combining first-principles calculations and machine learning(ML)techniques,we elucidate critical factors influencing the catalytic properties,taking Cu-based single atom alloys(SAAs)as examples.Our method relies on high-throughput calculations of 2669 CO adsorption configurations on 43 types of Cu-based SAAs with various surfaces.Extensive ML analyses reveal that low generalized coordination numbers and valence electron number are key features to determine catalytic performance.Applying our ML model with cross-group learning scheme,we demonstrate the model generalizes well between Cu-based SAAs with different alloying elements.Further,electronic structure calculations suggest surface negative center could enhance CO adsorption by back donating electrons to antibonding orbitals of CO.Finally,several SAAs,including PCu,AgCu,GaCu,ZnCu,SnCu,GeCu,InCu,and SiCu,are identified as promising CO_(2)RR catalysts.Our work provides a paradigm for the rational design and fast screening of SAAs for various electrocatalytic reactions.

An IR Study on Adsorption of CO and NO on Copper Ion-exchanged Zeolite Beta

Thee adsorption of CO and NO on copper ion-exchanged zeolite Beta was investigated using IR method.It was found that the thermalvacuum pretreatment procedure could result in the reduction of Cu2+ions in zeolite Beta.The adsorption of CO on Cu+sites in zeolite Beta closely follows Langmuir isotherm.Another Cu+species may form during the reaction between water and CO.The catalytic decomposition of NO on the zeolite was observed at room temperature,indicating that the decomposition reaction may occur between two coordinated NO ligands of the same dinitrosyhc complex.Furthermore,the appearance of two series of NO adsorption bands reveals that copper ions existing at different cation sites may have different effect on the adsorption and decomposition of NO molecules.

Parametric study on the mixed solvent synthesis of ZIF-8 nano- and micro-particles for CO adsorption: A response surface study

The room temperature synthesis of ZIF-8 micro-and nano-particles was investigated using a mixed methanol-water solvent system.ZIF-8 particles of good quality and high crystallinity were obtained.Response surface methodology was used to determine the effect of the synthesis conditions on the ZIF-8 yield,particle size distribution,and mean particle size.The ligand/metal salt molar ratio followed by the amount of sodium formate(the deprotonating agent)and then the amount of water(i.e,the composition of the mixed solvent)respectively had the largest effects on both the ZIF-8 yield and particle size.Results showed that mixing of solvents with different strengths in producing ZIF-8 crystals is a practical method to size-controlled synthesis of ZIF-8 particles.This method is more favorable for industrial-scale ZIF-8 synthesis than using excess amounts of ligands or chemical additives(like sodium formate).In addition,ZIF-8 samples with different mean particle sizes(100,500,and 1000 nm)were used for CO adsorption and the mid-sized ZIF-8 particles had the highest adsorption capacity.

Clarification of copper species over Cu-SAPO-34 catalyst by DRIFTS and DFT study of CO adsorption

In this work, the nature, location and evolution of Cu+ ions in Cu-SAPO-34 are investigated by diffuse reflectance infrared Fourier transform spectrum(DRIFTS) of CO adsorption and density functional theory(DFT) calculation. By combination with DFT results, characteristic Cu+–CO bands located at 2154 and 2136 cm.1 are attributed to CO adsorbed on Cu+ ions located at sites I(in the plane of six-membered ring connected to the large cages) and site II(in the eight-membered ring cages near the tilted four membered ring) in the framework of H-SAPO-34 zeolite. Subsequently, both the influences of Cu loading and preparation method are considered and discussed. By varying the Cu loading, the site-occupation preference of Cu+ ions on site I is confirmed,especially at low Cu loadings. Through elevating the desorption temperature, migration of Cu+ ions is revealed because of the adsorption-induced effect. Furthermore, a facile and more efficient approach to introduce Cu+ ions into CHA zeolite, compared with solid-state ion exchange with CuCl and conventional ion exchange in aqueous solution, and the different preparation methods also result in different occupations of Cu+ ions.

Probing active species for CO hydrogenation over ZnCr_(2)O_(4) catalysts

Oxide catalysts are increasingly employed for hydrogenation reactions,among which ZnCrOx is a major catalyst for the oxide-zeolite(OXZEO)process and for the hydrogenation of C1 molecules in general.Owing to the complex nature of ternary oxides,the surface and catalytic properties of ZnCr_(2)O_(4) spinel have remained controversial for CO hydrogenation.Combining in-situ Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy,we examined the adsorption and reaction of CO/H_(2) on the ZnCr_(2)O_(4) catalysts,which were pre-treated under oxidative or reductive conditions.The reduced ZnCr_(2)O_(4) catalyst was found to expose more surface sites for CO adsorption/reaction than the oxidized ZnCr_(2)O_(4) catalyst.Exposing the reduced ZnCr_(2)O_(4) to H_(2) at room temperature led to the formation of surface hydride species,which would transform into hydroxyl species at elevated temperatures.The reduced ZnCr_(2)O_(4) surface exhibited much stronger interaction with CO and H_(2) than ZnO and Cr_(2)O_(3).Exposing the reduced ZnCr_(2)O_(4) to the CO and H_(2)(1:1)mixture gas led to the hydrogenation of CO.However,CO was oxidized by the hydroxyl species via the water-gas-shift reaction,whereas the hydrogenation of CO could only be achieved by surface hydride species on the reduced ZnCr_(2)O_(4) to formyl or formate species at 373-473 K.Our study has thus shed light on the active species that control elementary reaction process of CO hydrogenation on complex oxide surfaces.

Effects of pretreatment and reduction on the Co/Al_2O_3 catalyst for CO hydrogenation

The purpose of this study was to investigate the effect of preadsorbed CO at different temperatures, calcination temperatures, the combined influence of reduction temperature and time, and pretreatment using hydrogen or syngas as reduction agents on the F-T synthesis （FTS） activity and selectivity of Co/Al2O3 catalyst. The reactivity of the carbon species at higher preadsorption temperature with H2 in TPSR decreased, whereas the carbon-containing species showed higher reactivity over Co/Al2O3 catalyst with low calcination temperature. This agreed well with the order of catalytic activity for F-T synthesis on this catalyst. The catalytic activity of the catalyst varied with reduction temperature and time remarkably. CODEX optimization gave an optimum reduction temperature of 756 K and reduction time of 6.2 h and estimated C5＋ yield perfectly. The pretreatment of Co/Al2O3 catalyst with different reduction agents （hydrogen or syngas） showed important influences on the catalytic performance. A high CO conversion and C5＋ yield were obtained on the catalyst reduced by hydrogen, whereas methane selectivity on the catalyst reduced by syngas was much higher than that on the catalyst reduced by hydrogen.

Atomic structures and electronic properties of Cr-doped ZnO(1010)surfaces

An integrated approach combining scanning tunneling microscopy(STM)and X-ray photoelectron spectroscopy(XPS)is used to investigate the atomic structures and electronic properties of Cr-doped ZnO(1010)surfaces.When deposited at 300 K,Cr at low surface coverage(<0.1 ML)appeared either as isolated atoms on the surface terrace of ZnO(1010)or substituting Zn atoms in the ZnO lattice.Their structural models could be identified from atomic-resolution STM images and their oxidation states were found as Cr^(3+)based on XPS measurements.Rectangular islands nucleated at step edges along the[0001]direction could also be observed during the initial growth of Cr at 300 K and were assigned as Cr islands.The density of Cr islands as well as their average size increased with the increasing of Cr surface loading.Thermal treatments at above 600 K could facilitate the decomposition of Cr islands and the re-dispersion of Cr atoms into the ZnO lattice,indicating a strong interaction between Cr and ZnO.The adsorption of CO at 78 K showed no preferential adsorption at Cr^(3+)sites embedded in the surface lattice of ZnO.However,the re-dispersion of Cr atoms into the ZnO bulk at above 600 K could induce a significant upward band bending,causing a negative shift of core level XPS peaks of Zn 2p and O 1s by~0.5–0.7 eV.Our study has thus constructed a model catalyst for Cr-doped ZnO and provided atomic insight for understanding ZnO-based catalysts.

Switching of CO_(2)hydrogenation selectivity via chlorine poisoning over Ru/TiO_(2)catalyst

It is fascinating to explore the distribution of CO_(2)hydrogenation products regulated by heterogeneous catalysts,as both the chemical state of surface metals and structure of the support itself of the supported catalysts may affect the performance of CO_(2)hydrogenation.Herein,the complete switching of CO_(2)hydrogenation products from CH4 to CO can be realized by induction of Cl into Ru/TiO_(2)catalyst.Density functional theory(DFT)calculations indicated that Cl ions were mainly located on the Ru metal sites of Ru/TiO_(2)catalysts.Bader charge analysis and Ru 3p X-ray photoelectron spectra(XPS)results suggested that electrons transferred from Ru to Cl,resulting in the decrease of electron density of Ru.In situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)of CO_(2)hydrogenation and CO adsorption proved that with the increase of the Cl ion content,the adsorption of CO on the catalyst surface was significantly weakened,and resulted in the high CO selectivity.Our work demonstrates the role of Cl ions in regulating the distribution of CO_(2)hydrogenation products,and provides new ideas for regulating other catalytic processes.

Enhance the activity of multi-carbon products for Cu via P doping towards CO_(2) reduction

Electronic structure engineering is a powerful method to tailor the behavior of adsorbed intermediates on the surface of catalysts,thus regulating catalytic activity towards CO_(2)electroreduction.Herein,we prepared a series of P-doped Cu catalysts for CO_(2)electroreduction into multi-carbon(C_(2+))products by regulating the surface electronic structure of Cu.The introduction of P could stabilize the surface Cu^(δ+)species,enhancing the activity for C_(2+)products via adjusting the adsorbed strength of the CO intermediates(~*CO).When the molar ratio of P to Cu was 8.3%,the catalyst exhibited a Faradaic efficiency of 64%for C_(2+)products,which was 1.9 times as high as that(33%)for Cu catalysts at the applied current density of 210 m A cm^(-2).Notably,at the applied current density of 300 mA cm^(-2),the P-doped Cu catalyst with the molar ratio of P to Cu of 8.3%exhibited the highest partial current density for C_(2+)products of 176 mA cm^(-2),whereas the partial current density for C_(2+)products over the Cu catalyst was only 84 mA cm^(-2).Mechanistic studies revealed that modulating the molar ratios of P to Cu regulated the adsorbed strength of~*CO.A moderate adsorbed strength of *CO induced by appropriate P doping was responsible for the facilitated C–C coupling process.