Formation Of CHx Research Articles

Active sites of the cobalt catalysts controlled by surface silanols of silicalite-1 in CO2 hydrogenation to ethanol

The soaring emissions of CO2 have resulted in an extreme climate crisis worldwide. One of the promising solutions is to hydrogenate the CO2 into ethanol. However, a significant challenge lies in the low activity or ethanol selectivity of the catalysts, hindering its industrialization. For the Co-based catalysts, regulation of the active cobalt valance state is crucial for boosting ethanol synthesis by CO hydrogenation. In this work, silicalite-1 (S-1) was used as support to control cobalt sites, which was synthesized by a novel grinding synthesis method. The S-1 can form Si-O-Co chemical bonds with cobalt particles by grafting cobalt atoms onto isolated silanols located on the external surface of S-1. The strong metal-support interactions originating from the Si-O-Co bonds stabilized the coexistence of Co0 and CoO (CoOx sites), preventing complete reduction to Co0 during reduction process. The S-1-supported catalysts with CoOx sites showed superior catalytic performance compared to other catalysts with only Co0 sites. The S-1-supported catalysts with Co loading of 5 wt% exhibited an ethanol selectivity of 27 % at 250 °C and 2 MPa, corresponding to a space–time yield (STY) of 0.83 mmolethanol·gcat−1·h−1. In situ DRIFTS and DFT calculation results demonstrated that Co0 sites facilitated the formation of CHx* species, whereas CoO sites favored the HCOO* species. The CHx* species on Co0 sites tended to be further hydrogenated to CH4, whereas the CHx* species on CoOx sites could be coupled with the HCOO* species, inhibiting the formation of CH4 and enhancing ethanol selectivity. Our work provides an approach to prepare highly efficient catalysts with controlled cobalt sites and deepens an insight into the roles of Co0 and CoO sites in CO2 hydrogenation to ethanol.

The bifunctional oxygen carrier K/LayCoxFe1-xO3 for the production of C2–C4 olefins via CO2 hydrogenation

Developing the bifunctional oxygen carrier with excellent oxygen mobility and catalytic activity is the key to chemical looping combustion coupled CO2 hydrogenation to light olefins. In this study, a series of K/LayCoxFe1-xO3 (x = 0, 0.2, 0.4, 0.6, y = 0.2, 0.4, 0.8) with oxygen vacancy-active metal dual active centers were constructed by the Co doping-La defect synergistic strategy to evaluate the oxygen release and catalytic performance. The results indicated that K/La0.4Co0.4Fe0.6O3 had high oxygen mobility, and its reduced state can be directly used for CO2 hydrogenation to light olefins (C2=-C4=). The selectivity of C2=-C4= was close to 30%, and the conversion rate of CO2 was 36%. Combined with various characterizations, the synergy of Co doping and La defects increased the oxygen vacancy and promoted the exsolved CoFe alloy under the reduction induction of chemical looping combustion. In situ DRIFTS reveals the dynamic equilibrium of the Formate-Methoxy mechanism and RWGS-FTS pathway. Oxygen vacancies are found to enhance the conversion of CO2 via the formate pathway, while metal active phases alter the product distribution by changing the evolution of intermediates. The Co7Fe3 and oxygen vacancy on K/La0.4Co0.4Fe0.6O3 promotes the formation of CHx∗ and C–C coupling through various intermediates, improving the selectivity of light olefins.

Size-dependent and sensitivity of copper particle in ternary CuZnAl catalyst for syngas to ethanol

Understanding particle size effect of metal on catalysis has great significance in scientific and industrial applications. Herein, CuZnAl catalysts with narrow Cu particle size distribution had been synthesized and investigated for syngas to ethanol. Selectivity toward to C2+OH sharply increased from 8.9% to 60.5% with the increase of Cu size from 11.8 to 38.3 nm, then it slightly increased to 68.6% when further increasing the size to 49.2 nm, which was attributed to the domination of Cu (111) facet and accompanied by the formation of Cu(111)-ZnO interface at larger Cu sizes, thereby weakened hydrogenation activity and facilitated CHx formation. The in-situ DRIFTS experiment revealed that carbon chain growth was processed by the insertion of CO*/CHO* into the CHx* and the coupling of CHx* and CO2 *. These results substantially broaden the understanding the size effect of Cu and provided guidance for design more active Cu-based catalyst for ethanol synthesis.

Crystallographic dependence of CO2 hydrogenation pathways over HCP-Co and FCC-Co catalysts

Efficient conversion of CO2 is of great significance for sustainable supply of chemicals and fuels. While Co-based catalysts are known to be effective for CO hydrogenation in Fischer-Tropsch synthesis, they work very differently in CO2 hydrogenation. This study reveals a crystallographic dependence of reaction pathways for CO2 hydrogenation on Co catalyst showing a new type of structure sensitivity and structure-activity-selectivity relationship for CO2 conversion to chemicals and fuels. The experimental work on CO2 conversion including steady-state isotopic transient kinetic analysis (SSITKA) using 13C-labeled CO2 shows a preferential CH4 formation over HCP-Co but dominant CO formation over FCC-Co. The density functional theory calculations indicate that CO2 does dissociate directly into chemisorbed CO* and O* on both HCP-Co and FCC-Co, but the CO* intermediates on HCP-Co prefer to be hydrogenated to form CH4 whereas the CO* on FCC-Co preferentially desorb to form CO. The significantly altered adsorption strength of CO* due to the presence of chemisorbed O* and CO2* species on the catalyst surface is responsible for the mechanistic disconnection in product selectivity between the CO2 and CO hydrogenation over Co catalysts. This study also shows that the addition of K to Co diminishes the direct impact of Co crystal structure, but improves the selectivity to C2+ hydrocarbons along with higher CO2 conversion. This seems to result from another pathway originating from HCOO* intermediate from bonding interaction of surface Co atoms with carbon in CO2, leading to the formation of CHx* whose coupling subsequently give rises to C2+ products. The present study sheds new light into the crystallographic structural sensitivity of CO2 hydrogenation towards the rational design of more selective catalysts for CO2 conversion.

Nickel Catalyst with Atomically-Thin Meshed Coating Fabricated with ALD for Improved Durability in Dry Reforming of Methane

Recent advances in natural gas recovery and applications have drawn much attention to the dry reforming of methane (DRM) with carbon dioxide (CO2). While nickel (Ni) nanoparticles are attractive catalysts for DRM reactions in terms of activity and cost, its practical application is plagued by the quick deactivation in the catalytic environment. In this talk, atomically thin meshed-like Co coating catalytic structure is designed and fabricated to decorate Ni nanoparticles via atomic layer deposition. The coating structure improve the catalytic activity and effectively eliminates carbon deposition for the DRM reaction. Optimized catalytic performance is achieved by fine tuning the density of Co coating on nickel particles. The meshed coating structures partition the Ni surface to prevent continuous carbon nanotubes network formation. The Co component helps stabilizing the metallic phase of Ni in the DRM reaction. The Co-Ni interfaces created are beneficial for reducing carbon intermediates CHx formation and accelerate carbon removal. The amount of carbon formation can be reduced to 2.9%, which is a significant improvement (reduction over 2 to 6 times) compared with a series of state-of-the-art research reports (8%-23%) on Ni-based catalysts in the severe coking temperature range (around 650 ºC). The Co coating layer provides physical confinement and also improves the thermal stability of Ni nanoparticles from sintering and agglomeration up to 850 ºC. The strategies of selective ALD have demonstrated unique advantages to design and fabricate the catalysts in atomic scale and provided insights to understand the structure–activity relationship in a more direct way.

Fischer–Tropsch Product Selectivity Modulation via an FeRh Nanocluster Composition Design

The reaction mechanism of *CHx formation in Fischer–Tropsch synthesis on various FeRh nanoclusters is studied using DFT calculations. We find that the energy barrier of *CH2 formation from hydrogen-assisted *CH2O dissociation can be directly modulated using the Fe/Rh composition ratio. Thermodynamic investigations and the natural bond orbital (NBO) analysis indicate that the barrier dropping of C–O bond scission in *CH2O can be ascribed to the interaction between the Fe and the O atoms. In particular, the *CH2 formation can be selectively stabilized with respect to the *CH3O formation using a local tri-Fe configuration on the FeRh nanocluster when the Fe ratio exceeds 50%. An optimal barrier may be achieved by carefully balancing the number of Rh and Fe atoms in the local configuration of the active site to stabilize both ends of the intermediates.

Nickel catalyst with atomically-thin meshed cobalt coating for improved durability in dry reforming of methane

Nickel nanoparticles are effective catalysts for the dry reforming of methane (DRM) in terms of catalytic activity and cost. Yet when applied to DRM reaction under realistic conditions, it is of great challenge overcoming the related durability problems due to sintering and coke deposition. Atomically thin meshed-like Co coating catalytic structure is designed and fabricated to decorate Ni nanoparticles via atomic layer deposition. The coating structure improves the catalytic activity and effectively eliminates carbon deposition for the DRM reaction. Optimized catalytic performance is achieved by fine tuning the density of Co coating on nickel particles. The meshed coating structure partitions the Ni surface to prevent continuous carbon nanotubes network formation. The Co component helps stabilizing the metallic phase of Ni in the DRM reaction. The Co-Ni interfaces created are beneficial for reducing carbon intermediates CHx formation and accelerate carbon removal. The amount of carbon formation can be reduced to 2.9%, which is a significant improvement (reduction over 2 to 6 times) compared with a series of state-of-the-art research reports (8–23%) on Ni-based catalysts in the severe coking temperature range (around 650 °C). The Co coating layer provides physical confinement and also improves the thermal stability of Ni nanoparticles from sintering and agglomeration up to 850 °C.

H+ ion-induced damage and etching of multilayer graphene in H2 plasmas

H+ ion-induced damage of multilayer graphene (MLG) is investigated using Molecular Dynamics simulations as H2 plasmas could provide a possible route to pattern graphene. Low-energy (5–25 eV) H+ cumulative bombardment of ABA-stacked MLG samples shows an increase of the hydrogenation rate with the ion dose and ion energy. At 5 eV, the H coverage grows with the ion fluence only on the upper-side of the top layer but saturates around 35%. Hydrogenation of multi-layers and carbon etching are observed at higher energies. Layer-by-layer peeling/erosion of the MLG sample is observed at 10 eV and occurs in two phases: the MLG sample is first hydrogenated before carbon etching starts via the formation of CHx (∼60%) and C2Hx (∼30%) by-products. A steady state is reached after an ion dose of ∼5 × 1016 H+/cm2, as evidenced by a constant C etch yield (∼0.02 C/ion) and the saturation of the hydrogenation rate. At 25 eV, an original etching mechanism—lifting-off the entire top layer—is observed at low fluences due to the accumulation of H2 gas in the interlayer space and the absence of holes/vacancies in the top layer. However, as the underneath layers contain more defects and holes, this Smartcut-like mechanism cannot be not repeated and regular ion-assisted chemical etching is observed at higher fluences, with a yield of ∼0.05 C/ion.

Insight into CHx formation in Fischer–Tropsch synthesis on the hexahedron Co catalyst: Effect of surface structure on the preferential mechanism and existence form

Spin-polarized density functional theory calculations have been performed to investigate the preferential mechanism of CHx(x=1–3) formation in Fischer-Tropsch synthesis on only the hexahedron Co(101¯0)-A and Co(10 1¯0) surfaces. Our results show that CO hydrogenation to CHO is favored compared to CO direct dissociation and hydrogenation to COH on these two surfaces. Starting from C and CHO, we further seek out the optimal pathways of CHx formation, suggesting that CHx is mainly formed through H-assisted CO dissociation pathways on Co(101¯0)-A surface, in which CH is form via CHO dissociation, CH2 and CH3 are formed through CH2O with the direct and H-assisted dissociation, respectively; meanwhile, CH2 hydrogenation also contributes to CH3 formation; CH2 and CH3 are the surface abundant species on Co(101¯0)-A surface. However, on Co(101¯1) surface, CHx species is formed through CO direct dissociation into C, followed by C successive hydrogenation, C and CH are the surface abundant species. Therefore, Co surface structure can affect the preferential formation pathways and the dominant existence form of CHx species. Moreover, CH3OH formation cannot compete with CHx formation on Co(101¯0)-A and Co(101¯1) surfaces, considering both surfaces covering 63% of the total surface area exposed of hexahedron Co surfaces, which depends on the reaction conditions, particle size, catalyst support, carbon deposition and many other factors, the contribution to the overall CHx sources from Co(101¯0)-A and Co(101¯1) surfaces even surpasses that of other hexahedron Co surfaces under the certain realistic conditions. As a result, the hexahedron Co surfaces exhibit high catalytic selectivity for CHx formation, and provide more CHx sources to participate into the F-T synthesis.

Unraveling the role of support surface hydroxyls and its effect on the selectivity of C2 species over Rh/γ-Al2O3 catalyst in syngas conversion: A theoretical study

The supported Rh-based catalysts exhibit the excellent catalytic performances for syngas conversion to C2 species. In this study, all possible elementary steps leading to C2 species from syngas have been explored to identify the role of support and its surface hydroxyls over Rh/γ-Al2O3 catalyst; Here, the results are obtained using density functional theory (DFT) method. Two models: Rh4 cluster supported on the dry γ-Al2O3(110) surface, D(Rh4), and on the hydroxylated γ-Al2O3(110) surface, H(Rh4), have been used to model Rh/γ-Al2O3 catalyst. Our results show that CO prefers to be hydrogenated to CHO, subsequently, starting from CHO species, CH and CH2 species are the dominate monomers among CHx(x=1–3) species rather than CH3 and CH3OH on D(Rh4) and H(Rh4) surfaces, suggesting that γ-Al2O3-supported Rh catalyst exhibits the high selectivity towards CHx formation compared to the pure Rh catalyst. On the other hand, D(Rh4) is more favorable for C2 hydrocarbon (C2H2) formation, whereas H(Rh4) surface easily produces C2 hydrocarbon (C2H2) and C2 oxygenates (CHCO,CH2CHO), indicating that the surface hydroxyls of support can affect the selectivity of C2 species over Rh/γ-Al2O3 catalyst in syngas conversion. Moreover, compared to the pure Rh(111) surface, Rh/γ-Al2O3 catalyst can achieve the excellent catalytic performances for syngas conversion to C2 species.

Fischer-Tropsch Synthesis, Catalysts, and Catalysis: Advances and Applications (Chemical Industries 142)

Spin-polarized density functional theory calculations have been performed to investigate the preferential mechanism of CHx(x = 1–3) formation in Fischer-Tropsch synthesis on only the hexahedron Co(101¯0)-A and Co(101¯0) surfaces. Our results show that CO hydrogenation to CHO is favored compared to CO direct dissociation and hydrogenation to COH on these two surfaces. Starting from C and CHO, we further seek out the optimal pathways of CHx formation, suggesting that CHx is mainly formed through H-assisted CO dissociation pathways on Co(101¯0)-A surface, in which CH is form via CHO dissociation, CH2 and CH3 are formed through CH2O with the direct and H-assisted dissociation, respectively; meanwhile, CH2 hydrogenation also contributes to CH3 formation; CH2 and CH3 are the surface abundant species on Co(101¯0)-A surface. However, on Co(101¯1) surface, CHx species is formed through CO direct dissociation into C, followed by C successive hydrogenation, C and CH are the surface abundant species. Therefore, Co surface structure can affect the preferential formation pathways and the dominant existence form of CHx species. Moreover, CH3OH formation cannot compete with CHx formation on Co(101¯0)-A and Co(101¯1) surfaces, considering both surfaces covering 63% of the total surface area exposed of hexahedron Co surfaces, which depends on the reaction conditions, particle size, catalyst support, carbon deposition and many other factors, the contribution to the overall CHx sources from Co(101¯0)-A and Co(101¯1) surfaces even surpasses that of other hexahedron Co surfaces under the certain realistic conditions. As a result, the hexahedron Co surfaces exhibit high catalytic selectivity for CHx formation, and provide more CHx sources to participate into the F-T synthesis.

Ethanol oxidation on shape-controlled platinum nanoparticles at different pHs: A combined in situ IR spectroscopy and online mass spectrometry study

Ethanol oxidation on different shape-controlled platinum nanoparticles at different pHs was studied using electrochemical, Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and, especially, Differential Electrochemical Mass Spectrometry (DEMS) techniques, the latter giving interesting quantitative information about the products of ethanol oxidation. Two Pt nanoparticle samples were used for this purpose: (100) and (111) preferentially oriented Pt nanoparticles. The results are in agreement with previous findings that the preferred decomposition product depends on surface structure, with COads formation on (100) domains and acetaldehyde/acetic acid formation on (111) domains. However, new information has been obtained about the changes in CHx and CO formation at lower potentials when the pH is changed, showing that CHx formation is favored against the decrease in CO adsorption on (100) domains. At higher potentials, complete oxidation to CO2 occurs from both CHx and CO fragments. In (111) Pt nanoparticles, the splitting of CC bond is hindered, favoring acetaldehyde and acetate formation even in 0.5M H2SO4. C1 fragments become even less when the pH increases, being nearly negligible in the highest pH studied.

A density functional theory study on the conversion of ethylene to carbon monomer on PdAu(1 0 0) surface

Calculations based on the first-principles density functional theory (DFT) were performed to study the possible transformation pathways of ethylene on PdAu(100) surface to investigate the effect of Au atom alloying with Pd on the formation of CHx (x=0–2), which may eventually form carbon monomer and lead to the deactivation of catalysts. The energetic properties of reactions including the scission of the CH, CC bond and a hydrogen-shift process were determined. The CH bond scission is confirmed to be prone to happen on the studied surface, while it is difficult for the CC bond scission to occur due to relatively high barriers, the values of which are as high as 2.72–4.62eV. The activation barriers for all related reactions except for the dehydrogenation of vinyl, vinylidene and acetenyl demonstrate that it is harder for the conversion of ethylene to occur on PdAu(100) surface than on Pd(100) surface, especially for the CC bond scission. All the results indicate that the alloying of Au atom with pure Pd catalyst can prevent the formation of carbon monomer, which may notably affect properties of catalysts.

Methane, formaldehyde and methanol formation pathways from carbon monoxide and hydrogen on the (0 0 1) surface of the iron carbide χ-Fe5C2

Formation of CHx(O) monomers and C1 products (CH4, CH2O, and CH3OH) on C-terminated χ-Fe5C2(001) (Hägg carbide) surfaces of different carbon contents was investigated using periodic DFT simulations. Methane (CH4) as well as monomer (CHx) formation follows a Mars–van Krevelen-like cycle starting with the hydrogenation of surface carbidic carbon, which is regenerated by subsequent CO dissociation, while oxygen is removed as H2O. In cases where surface carbon is readily available, the apparent barrier for CH4 formation was found to be ∼95kJ/mol. However, different rate-determining steps show that different propagation mechanisms may be possible for actual chain growth, depending on the carbon content of the surface. Hydrogen addition to CO forms formyl (HCO), which is a precursor for both H-assisted CO activation and oxygenate formation. Further hydrogenation of HCO yields adsorbed formaldehyde and methoxy, rather than hydroxymethyl (HCOH) that would give C–O bond splitting. Full hydrogenation to gas-phase methanol faces a high barrier, suggesting that CHxO species may be involved in higher oxygenate formation in a full Fischer–Tropsch mechanism or that the C–O bond does not break until the CHO fragment has been incorporated in a C2 species, a route for which precedents are available in the literature.

Source and major species of CHx(x = 1–3) in acetic acid synthesis from methane–syngas on Rh catalyst: a theoretical study

Density functional calculations have been carried out to investigate the source and major species of CHx (x = 1–3) involved in acetic acid synthesis from methane–syngas on the Rh(111) surface. All possible formation pathways of CHx (x = 1–3) from methane and syngas have been systematically investigated. For CHx formation from methane, our results show that CH is the most abundant species; for CHx formation from syngas, all CHx (x = 1–3) species form from CHO by CO hydrogenation, and the optimal formation routes of CHx show that CH and CH3 are the most abundant species rather than CH2 and CH3OH. On the other hand, CH formed by methane is more favourable than CH and CH3 formed by syngas; meanwhile, CO insertion into CHx species to form C2 oxygenates as acetic acid precursors is more favourable than CO hydrogenation to CH and CH3. As a result, in acetic acid synthesis from methane–syngas, CHx (x = 1–3) species come from methane rather than syngas, and the corresponding primary species is CH. In addition, the CO in syngas is predominantly responsible for insertion reactions that produce CHCO, which is a C2 oxygenate precursor leading to the formation of acetic acid. Furthermore, microkinetic modelling analysis shows that the major product of acetic acid synthesis from methane–syngas on the Rh(111) surface is CH3COOH, and that the production of CH3OH cannot compete with that of CH3COOH.

Oxygen Attachment on Alkanethiolate SAMs Induced by Low-Energy Electron Irradiation

Reactions of (18)O2 with self-assembled monolayer (SAM) films of 1-dodecanethiol, 1-octadecanethiol, 1-butanethiol, and benzyl mercaptan chemisorbed on gold were studied by the electron stimulated desorption (ESD) of anionic fragments over the incident electron energy range 2-20 eV. Dosing the SAMs with (18)O2 at 50 K results in the ESD of (18)O(-) and (18)OH(-). Electron irradiation of samples prior to (18)O2 deposition demonstrates that intensity of subsequent (18)O(-) and (18)OH(-) desorption signals increase with electron fluence and that in the absence of electron preirradiation, no (18)O(-) and (18)OH(-) ESD signals are observed, since oxygen is unable to bind to the SAMs. A minimum incident electron energy of 6-7 eV is required to initiate the binding of (18)O2 to the SAMs. O2 binding is proposed to proceed by the formation of CHx-1(•) radicals via resonant dissociative electron attachment and nonresonant C-H dissociation processes. The weaker signals of (18)O(-) and (18)OH(-) from short-chain SAMs are related to the latter's resistance to electron-induced damage, due to the charge-image dipole quenching and electron delocalization. Comparison between the present results and those for DNA oligonucleotides self-assembled on Au (Mirsaleh-Kohan, N. et al. J. Chem. Phys. 2012, 136, 235104) indicates that the oxygen binding mechanism is common to both systems.

Insight into the Preference Mechanism of CHx (x = 1–3) and C–C Chain Formation Involved in C2 Oxygenate Formation from Syngas on the Cu(110) Surface

The possible formation pathways of CHx (x = 1–3) and C–C chain involved in C2 oxygenate formation from syngas on an open Cu(110) surface have been systematically investigated to identify the preference mechanism of CHx (x = 1–3) and C–C chain formation. Here, we present the main results obtained from periodic density functional calculations. Our results show that all CHx (x = 1–3) species formation starts with CHO hydrogenation; among them, CHx (x = 2, 3) are the most favored monomers, however, CH3OH is the main product from syngas on the Cu(110) surface, and the formation of CHx (x = 1–3) cannot compete with CH3OH formation. Further, on the basis of the favored monomer CHx (x = 2, 3), we probe into the C–C chain formation of C2 oxygenates by CO or CHO insertion into CHx (x = 2, 3), as well as the hydrogenation, dissociation, and coupling of CHx (x = 2, 3), suggesting that CO insertion into CH2 to form C2 oxygenates is the dominant reaction for CH2 on the Cu(110) surface with an activation barrier of 44.5...

Monomer Formation Model versus Chain Growth Model of the Fischer–Tropsch Reaction

One of the great challenges in molecular heterogeneous catalysis is to model selectivity of a heterogeneous catalytic reaction based on first principles. Molecular kinetics simulations of the Fischer–Tropsch reaction, which converts synthesis gas into linear hydrocarbons, demonstrate the need for microkinetics approaches that do not make a priori choices of rate controlling steps. A key question pertaining to this reaction, in which hydrocarbons are formed through consecutive insertion of adsorbed CHx monomers into adsorbed growing hydrocarbon chains, is whether the CO consumption rate depends on the rate of the CHx insertion polymerization process. Microkinetic theory of this heterogeneous catalytic reaction based on quantum-chemical data is used to deduce expressions for the CO consumption rate and chain growth parameter α in the two limiting cases where chain growth rate is fast compared to the formation of CHx (monomer formation limit) or where the reverse relation holds (chain growth limit). The conventional assumptions that CHx formation is rate controlling and that change in CO coverage due to reaction is negligible lead to substantial overestimation of the rate of CO consumption. It appears that intermediate reactivity of the catalytic reaction center, with neither too low nor too high activation energies for C–O bond cleavage, and low reagent gas pressure lead to such monomer formation limiting type behavior, whereas maximum rate of CO consumption is found when chain growth rate is limiting.

Experimental and Theoretical Study on the Ethane and Acetylene Formation from Electron Irradiation of Methane Ices

In this work we present an experimental and theoretical study on the formation of ethane and acetylene from solid methane condensed at 20 K and irradiated with a 500 - 3000 eV electron beam. The experiments were monitored with Thermal Desorption Spectroscopy. We observe that the electron irradiation induced a dehydrogenation of methane and a consequent formation of CHx (x = 1, 2, 3) fragments. Furthermore, in the solid during irradiation, a simple recombinetion reaction in the solid between two adjacent CHx molecules may form HC≡CH, H2C=CH2, and H3C-CH3 with a triple, double, and single carbon-carbon bond, respectively. The formed amount of ethane and acetylene increases with irradiation time and reaches a saturation value.

Insights into the preference of CHx(x = 1–3) formation from CO hydrogenation on Cu(111) surface

The mechanisms of CHx(x=1-3) formation from CO hydrogenation on Cu(111) surface have been systematically investigated using periodic density functional calculations. The activation barriers and reaction energies for all the elementary steps involved in CHx(x=1-3) formation is presented here. CO hydrogenation and its dissociation have been discussed. Our results show that the CO dissociation route is less energetically favored on Cu(111) surface than CO hydrogenation to form CHO and COH, in which CO mainly goes through hydrogenation to form CHO, meanwhile, the formation of CHO is more favorable both kinetically and thermodynamically than that of COH. Starting from CHO, we further investigate the formation of CHx(x=1-3), two conditions, without H-assisted and with H-assisted, are considered. As a result, we seek out the optimal paths of CHx(x=1-3) formation and the corresponding activation barrier of rate-controlled step on Cu(111) surface, moreover, among all CHx(x=1-3) species, CH2 and CH3 are the most favored monomer for CO hydrogenation on Cu(111). In addition, our results show that CH3OH is also easily formed by CO hydrogenation, and the formations of CH2, CH3 and CH3OH by CO hydrogenation compete with each other on Cu(111) surface.