CO Dissociation Research Articles

Comparison of helium and argon for the production of carbon monoxide (CO) by a plasma jet for biomedical applications

Carbon monoxide (CO) has anti-inflammatory properties and its production by plasma could be a significant advantage in the field of plasma medicine. We characterized a pulsed kHz-driven plasma jet to produce CO for biomedical applications. With no target interaction, the CO2 conversion into CO, the breakdown voltage and energy delivered to the plasma were investigated for two noble carrier gases: helium and argon. The breakdown voltage and the energy delivered to the plasma in argon gas were twice as high as in helium. The breakdown voltage was barely affected by the gas flow rate and the applied voltage, while it decreased slightly with the excitation frequency because the amount of residual charges increases with the frequency. However, the energy delivered to the plasma was not particularly affected by a change in frequency or gas flow rate, while it increased linearly with the applied voltage. CO production rose from a couple of ppm to about 2000 ppm for a specific energy input from 2 to 2000 J/L (5 × 10−4 to 5200 × 10−4 eV/(atom or molecule)), making this plasma source safe in terms of CO production for biomedical applications. Unlike literature results, the nature of the noble carrier gas did not have an impact on CO production. The CO concentration produced with 0.3% CO2 admixture increased linearly with the specific energy input (SEI) until reaching a plateau at about 2100ppm. This implies that loss processes were negligible and that CO2 dissociation was mainly due to energetic particles such as electrons and excited noble atoms. The conversion decreased with the ratio of CO2. Helium and argon as carrier gases are equivalent in terms of CO production and the CO concentration can be controlled by the SEI and the ratio of CO2.

Insights into reduction of CO2 to CO catalyzed by pyramidal-4Ni clusters supported on doped CeO2(111)

Converting CO2 into valuable chemicals has become a widely used research method for CO2 conversion. In this work, the catalytic performance of pyramidal-4Ni catalysts supported on rare earth metal-doped CeO2 toward CO2 reduction reaction (CO2RR) was investigated by using density-functional theory calculations. For rare earth metal-doped CeO2, 2Ce is substituted by 2 trivalent cations and at the same time one oxygen vacancy is created to make charge compensation. We investigated the oxygen vacancy nearest (VO,N) and next-nearest (VO,NN) to 4Ni, and found releasing CO and CO2 dissociation are the rate-determining steps, respectively, via the path of VO,N and VO,NN. Among the studied dopants (Ga, Sb, Lu, Gd, Pr, La, Bi), Gd is identified as the best dopant for catalyzing the reduction of CO2 at 823 K, with the turn-over frequency (TOF) of 104 times as large as that over 4Ni supported on pure CeO2. This exploration pro-vides theoretical support and guidance for the research and application of rare earth metaldoped CeO2-loaded Ni catalysts in the field of CO2 reduction.

An improved semi-global intrinsic kinetics model for high temperature carbon oxidation

Measurements of the oxidation rates of various forms of carbon (soot, graphite, coal char) have often shown an unexplained attenuation with increasing temperatures in the vicinity of 2000 K, even when accounting for diffusional transport limitations and gas-phase chemical effects (e.g. CO2 dissociation). With the development of oxy-fuel combustion approaches for pulverized coal utilization with carbon capture, high particle temperatures are readily achieved in sufficiently oxygen-enriched environments. In this work, a new semi-global intrinsic kinetics model for high temperature carbon oxidation is created by starting with a previously developed 5-step mechanism that was shown to reproduce all major known trends in carbon oxidation, except for its high temperature kinetic falloff, and incorporating a recently discovered surface oxide decomposition step. The predictions of this new model are benchmarked by deploying the kinetic model in a steady-state reacting particle code (SKIPPY) and comparing the simulated results against a carefully measured set of pulverized coal char combustion temperature measurements over a wide range of oxygen concentrations in N2 and CO2 environments. The results show that the inclusion of the spontaneous surface oxide decomposition reaction step significantly improves predictions at high particle temperatures. Furthermore, the simulations reveal that O atoms released from the oxide decomposition step enhance the radical pool in the near-surface region and within the particle interior itself. Incorporation of literature rates for O and OH reactions with the carbon surface results in a reduction in the predicted radical pool concentrations and a very minor enhancement of the overall carbon oxidation rate.

Computational screening of single-atom doped In2O3 catalysts for the reverse water gas shift reaction.

The reverse water gas shift (RWGS) reaction is an important method for converting carbon dioxide (CO2) into valuable chemicals and fuels by hydrogenation. In this paper, the catalytic activity of single-atom metal-doped (M = Pt, Ir, Pd, Rh, Cu, Ni) indium oxide (c-In2O3) catalysts in the cubic phase for the RWGS reaction was investigated using density functional theory (DFT) calculations. This was achieved by identifying metal sites, screening oxygen vacancies, followed by further calculating the energy barriers for the direct and indirect dissociation pathways of the RWGS reaction. Our results show that the single-atom dopant in the indium oxide lattice promotes the creation of oxygen vacancies on the In2O3 surface, thereby facilitating the adsorption and activation of CO2 by the oxide surface and initiating the subsequent RWGS reaction. Furthermore, we find that the oxygen vacancy (OV) formation energy on the surface of the single-atom metal doped c-In2O3(111) surface can be used as a descriptor for CO2 adsorption, and the higher the OV formation energy, the more stable the CO2 adsorption structure is. The Cu/In2O3 structure has relatively high energy barriers for both direct (1.92 eV) and indirect dissociation (2.09 eV) in the RWGS reaction, indicating its low RWGS reactivity. In contrast, the Ir/In2O3 and Rh/In2O3 structures are more conducive to the direct dissociation of CO2 into CO, which may serve as more efficient RWGS catalysts. Furthermore, microkinetic simulations show that single atom metal doping to In2O3 enhances CO2 conversion, especially under high reaction temperatures, where the formation of oxygen vacancies is the limiting factor for CO2 reactivity on the M/In2O3 (M = Cu, Ir, Rh) models. Among these three single-atom catalysts, the Ir/In2O3 model was predicted to have the best CO2 reactivity at reaction temperatures above 573 K.

CO2 activation by copper oxide clusters: size, composition, and charge state dependence.

The interaction of CO2 with copper oxide clusters of different size, composition, and charge is investigated via infrared multiple-photon dissociation (IR-MPD) spectroscopy and density functional theory (DFT) calculations. Laser ablation of a copper target in the presence of an O2/He mixture leads to the preferred formation of oxygen-rich copper oxide cluster cations, CuxOy+ (y > x; x ≤ 8), while the anionic cluster distribution is dominated by stoichiometric (x = y) and oxygen-deficient (y < x; x ≤ 8) species. Subsequent reaction of the clusters with CO2 in a flow tube reactor results in the preferred formation of near-stoichiometric CuxOy(CO2)+/- complexes. IR-MPD spectroscopy of the formed complexes reveals the non-activated binding of CO2 to all cations while CO2 is activated by all anions. The great resemblance of spectra for all sizes investigated demonstrates that CO2 activation is largely independent of cluster size and Cu/O ratio but mainly determined by the cluster charge state. Comparison of the IR-MPD spectra with DFT calculations of the model systems Cu2O4(CO2)- and Cu3O4(CO2)- shows that CO2 activation exclusively results in the formation of a CO3 unit. Subsequent CO2 dissociation to CO appears to be unfavorable due to the instability of CO on the copper oxide clusters indicating that potential hydrogenation reactions will most likely proceed via formate or bicarbonate intermediates.

H-assisted CO2 dissociation on PdnPt(4-n)/In2O3 catalysts: a density functional theory study.

CO2 hydrogenation into valuable chemical compounds can effectively address the issues of greenhouse gas emissions and energy scarcity. The activation and dissociation processes of CO2 are crucial for its reduction reactions, but the effects of *H adatoms on the C-O cleavage are still confusing. This study investigates the H-assisted CO2 dissociation pathways on the PdnPt(4-n)/In2O3 (n = 0-4) catalysts via DFT calculation. Initially, the adsorption properties of *H2, *COOH, and *HCOO species are calculated. Then, two H-assisted CO2 dissociation channels, i.e., *CO2 + *H → *COOH → *CO + *OH and *CO2 + *H → *HCOO → *CHO + *O, are studied. Results show that Pt and Pd promote the CO2 hydrogenation and C-O bond cleavage reactions, respectively. In comparison to CO2 direct dissociation, the COOH-mediated and HCOO-mediated channels facilitate and impede the C-O bond cleavage, respectively. Overall, the Pd3Pt/In2O3 constituent is suggested for the H-assisted CO2 dissociation reaction. The electronic effects of the PdnPt(4-n) bimetals adjust the stabilities of the intermediates and barriers of the elementary steps, and the interactions between PdnPt(4-n) and In2O3 provide extra sites for the adsorbates and reaction steps. This study reveals the effects of *H on the C-O bond dissociation processes and provides useful insight into designing PdPt/In2O3 catalysts for CO2 hydrogenation reactions.

Intramolecular electrostatic effects on reduction of CO2 to CO by iron porphyrin complexes: Insights from DFT calculations

Iron porphyrin (Por) complexes were found to be highly efficient molecular catalysts for electrocatalytic CO2 reduction and the catalytic performance can be modulated by the modification of ligands. Herein, density functional theory calculations were employed to investigate how the presence of second-sphere anionic carboxylate groups influences the CO2-to-CO conversion by Fe porphyrins. The kinetics and thermodynamics of individual chemical steps in the reaction cycle were systematically studied. Computations indicated that the catalytic active species is the ferrous complex with the two extra electrons being stored in the π system of porphyrin and the rate-determining step is the CO2 binding. The synchronization of the Fe-to-CO2 and ligand-to-Fe electron transfers leads to the formation of FeIII(CO22−)(Por•−). The experimentally observed activity trend could be rationalized by the Brønsted-Evans-Polanyi principle. The electrostatic repulsive between the negatively charged hanging group and the CO2 moiety destabilizes the CO2 adduct and thereby raises the binding energy. Then, the two-step protonation occurs easily to give Fe(II)-CO. The further one-electron reduction triggers the dissociation of CO to regenerate of the formal Fe(I) porphyrin catalyst. The insights gained from this study may be helpful in designing efficient electrocatalysts for CO2 reduction.

Insights into the contribution of oxygen vacancies on CO2 activation for dry reforming of methane over ceria-based solid solutions

Exploring the contribution of oxygen vacancies in ceria-based materials is critical for understanding the role they play in catalysis. In this study, a series of aliovalent (La3+, Nd3+, Sm3+, and Eu3+) metal ions ceria-based solid solutions were synthesized and comparatively characterized for their application in dry reforming of methane (DRM). The concentration and reactivity of oxygen vacancies either on the surface or in the bulk, which are identified as active sites for direct CO2 dissociation, were calculated through a combination of transient response experiments and numerical simulations. The results show that the substitution of Ce4+ with trivalent ions increases oxygen vacancies, which improves the activation of CO2 and facilitates the oxidation of the formed coke. The CO2 activation rate was identified as a descriptor for predicting the catalytic stability. This work demonstrates the composition-dependent interplay among ceria-based materials and provides a pathway to tailor the reactivity of ceria-based catalysts.

CO2 activation and dissociation on the Fe2O3/Cu(111) inverse catalyst: A dispersion-corrected DFT study

Density functional calculations have been performed to study the adsorption and dissociation of CO2 on a model of Fe2O3/Cu(111) inverse catalyst employing the PBE-D3 functional. The adsorption of the Fe2O3 cluster on Cu(111) surface was found to be highly exothermic accompanied by a noticeable deformation of its structure. An electronic charge transfer from Cu to Fe2O3 was observed and the appearance of a partially occupied Fe 4 s electronic state around the Fermi level was evidenced. This available electronic charge plays a significant role in the subsequent CO2 adsorption. This molecule adsorbs preferentially at the oxide–metal interface with a bent geometry. The adsorption involves a charge transfer from Fe2O3/Cu(111) to CO2, yielding an activated CO2δ- species. On pristine Cu(111) and Fe2O3(0001) surfaces, the CO2 adsorption is weaker, and the almost null charge transfer indicates a non-activated CO2 molecule. The dissociation of CO2 on Fe2O3/Cu(111) was calculated to be slightly exothermic, endothermic on Cu(111) and strongly endothermic on Fe2O3(0001). The activation barrier for CO2 dissociation was found to be 0.90 eV on Fe2O3/Cu(111), significantly lower than on Cu(111) and Fe2O3(0001). Our calculations show a great potential for the use of Fe2O3/Cu(111) inverse catalysts in reactions involving CO2 activation and dissociation.

A High-Entropy Layered Perovskite Coated with In Situ Exsolved Core-Shell CuFe@FeOx Nanoparticles for Efficient CO2 Electrolysis.

Solid oxide electrolysis cells (SOECs) are promising energy conversion devices capable of efficiently transforming CO2 into CO, reducing CO2 emissions, and alleviating the greenhouse effect. However, the development of a suitable cathode material remains a critical challenge. Here a new SOEC cathode is reported for CO2 electrolysis consisting of high-entropy Pr0.8 Sr1.2 (CuFe)0.4 Mo0.2 Mn0.2 Nb0.2 O4-δ (HE-PSCFMMN) layered perovskite uniformly coated with in situ exsolved core-shell structured CuFe alloy@FeOx (CFA@FeO) nanoparticles. Single cells with the HE-PSCFMMN-CFA@FeO cathode exhibit a consistently high current density of 1.95 A cm-2 for CO2 reduction at 1.5V while maintaining excellent stability for up to 200 h under 0.75 A cm-2 at 800°C in pure CO2 . In situ X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations confirm that the exsolution of CFA@FeO nanoparticles introduces additional oxygen vacancies within HE-PSCFMMN substrate, acting as active reaction sites. More importantly, the abundant oxygen vacancies in FeOx shell, in contrast to conventional in situ exsolved nanoparticles, enable the extension of the triple-phase boundary (TPB), thereby enhancing the kinetics of CO2 adsorption, dissociation, and reduction.

Evaluating CO2 hydrate kinetics in multi-layered sediments using experimental and machine learning approach: Applicable to CO2 sequestration

The transition to a low-carbon economy requires the implementation of effective carbon capture and sequestration (CCS) strategies. One of the potential CCS strategies is to capture industrial CO2 emissions and inject them into the oceanic sediments to be stored as CO2 hydrates. However, the success of this technique depends on a few key factors such as the type of sediments where CO2 is injected, the kinetics of CO2 hydrate formation and dissociation, the accuracy of the models for prediction of formation kinetics, and the CO2 hydrates morphology. So, in this first-gen work, a highly complex set of experiments was carried out to examine the CO2 hydrate formation and dissociation processes by injecting CO2 via injection tube into different size wet sediments, i.e., coarse (diameter: 0.5–1.5 mm), granules (diameter:1.5–3.0 mm) and dual-layered sand (coarse + granules), embedded inside high-pressure reactor as the artificial seabed. The experiments were carried out at 3.5 MPa at T = 1.5–2.0 °C with 500 ppm of the eco-friendly hydrate promotor (l-tryptophan). The images of morphological changes during hydrate formation/dissociation, the Scanning Electron Microscope analysis of the sediments, and the estimated water-to-hydrate conversations have been reported in this work. A novel mathematical four-parameter-based CO2 hydrate kinetics model was also developed. A set of 32,843 experimental data points was used to train a supervised machine learning algorithm using two parameters with the other two taken from published literature. The water-to-hydrate conversion was estimated and follows the order of dual-layered sand [88.26 (±4.62) %] > coarse [77.77 (±5.72) %] > granules [65.36 (±2.3) %]. The proposed ML-based model predicted the water-to-hydrate conversion with an Average Absolute Relative Deviation [%AARD] of 4.23–13.29 %. This work serves as a step forward in developing a sustainable hydrate-based oceanic carbon storage technology.

Comprehensive kinetic modeling of the Fischer Tropsch synthesis over the Ru–Co@C(Z-d)@void@CeO2 catalyst based on a molecular dynamics evaluated mechanism

Fischer Tropsch synthesis (FTS) is a promising catalytic solution to achieve ultra-clean fuel in which catalyst has a significant role. Even though several kinetic models have been rendered for it, representing a new one based on a meticulous mechanism is noteworthy, particularly when employing a novel catalyst. Hence, in this work, molecular dynamic (MD) simulation is utilized to identify the appropriate pathway from the viewpoint of minimum energy of the elementary reactions. In this regard, we consider a majority of plausible FTS elementary reactions over Ru–CO@C(Z-d)@void@CeO2 (cobalt carbon-MOF based plus ruthenium and ceria with porous structure) catalyst, and by employing MD computations forward and reverse activation energy barrier values for each reaction are evaluated. Then, based on the minimum energy pathway (MEP), the appropriate mechanism is derived, which is inferred from the H-assisted CO dissociation pathway for the beginning step. Subsequently, a kinetic model is developed based on this mechanism, and the model parameters are correlated and optimized employing the genetic and Levenberg-Marquardt algorithms, respectively. In addition, we use various statistical methods to assess the significance of the model. For instance, the Mean Absolute Percentage Deviation (MAPD) of the correlated values from the experimental value is 4.46%. Additionally, the relative residual percentage (RR%) plots illustrate that 99% of the correlated data have less than a 10% deviation.

Investigation of the role of oxygen vacancies in CuZn catalysts for the formation of higher alcohols from syngas

The catalytic conversion of syngas to higher alcohols (C2+OH) has drawn widespread attention because it can alleviate the oil crisis and realize the clean and efficient use of coal. Nevertheless, the seesaw problem between C2+OH and total alcohol selectivity has not been solved. In recent years, catalytic processes involving oxygen vacancies have been widely investigated. However, the existing literature on this topic is fragmentary and unsystematic. Herein, we report a significant improvement in C2+OH synthesis by varying the oxygen vacancies on CuZn catalysts and systematically elaborate the structural and catalytic effects of the oxygen vacancies. Oxygen vacancy content shows almost linear positive correlations with many of the physical and chemical properties of the catalysts, such as SBET, Vp, Dp, Cu0 size, H2 consumption, and Cu0/(Cu0 + Cu+) ratio. The presence of oxygen vacancies drives catalysis in two ways. One, the dissociation of water adsorbed on oxygen vacancies causes the formation of hydroxyl groups, which interact with activated CO* to form surface formate (HCOO*) groups. This is followed by successive hydrogenation to form surface CHxO* intermediates. The CHxO* or CO* species are then coupled with surface CHx* to form ethanol on Znδ+ defect sites, realizing the growth of carbon chains. Two, oxygen vacancies drive electron transfer from ZnO to Cu, generating more Znδ+ defects and regulating the Cu0/(Cu0 + Cu+) ratio. The presence of electron-rich Cu is conducive to CO dissociation and adsorption, which promotes the formation of the critical surface intermediate CHx*. Consequently, the optimized CZ-0.80 catalyst exhibits exceptional catalytic performance, achieving 9.98 % CO conversion as well as ethanol and C2+OH proportions of up to 54.27 % and 59.95 %, respectively. Thus, by developing a new catalyst system that avoids the use of F-T elements such as Co or Fe for C2+OH synthesis from syngas, this work provides a new understanding of the growth of carbon chains.

CO2 and H2 Activation on Zinc-Doped Copper Clusters.

Here we systematically investigate the CO2 and H2 activation and dissociation on small Cun Zn0/+ (n=3-6) clusters using Density Functional Theory. We show that Cu6 Zn is a superatom, displaying an increased HOMO-LUMO gap and is inert towards CO2 or H2 activation or dissociation. While other neutral clusters weakly activate CO2 , the cationic clusters preferentially bind the CO2 in monodentate nonactivated way. Notably, Cu4 Zn allows for the dissociation of activated CO2 , whereas larger clusters destabilize all activated CO2 binding modes. Conversely, H2 dissociation is favored on all clusters examined, except for Cu6 Zn. Cu3 Zn+ and Cu4 Zn, favor the formation of formate through the H2 dissociation pathway rather than CO2 dissociation. These findings suggest the potential of these clusters as synthetic targets and underscore their significance in the realm of CO2 hydrogenation.

Preparation of layered double oxides encapsulated in carbon nanotubes to boost selective synthesis of higher alcohols from syngas: Modifying hydrogenation activity and restricting particle sizes by confinement effect

In this work, CuZnAl layered double oxides (LDOs) were encapsulated in carbon nanotubes (CNTs) with different diameters by an ultrasonic-assisted sol-gel method. The CuZnAl LDOs filled in CNTs showed higher catalytic activity and good selectivity for higher alcohols. The catalysts were investigated by varied characterization technologies in order to explore confinement effect of CNTs. It is found that distortion of octahedral unit structure in LDH precursor is enhanced by confinement effect of CNTs. The electron-deficient inner surfaces of CNTs are responsible for the efficient dissociation of CO adsorbed inside CNTs. In addition, hydrogenation ability of the LDOs filled in CNTs is improved due to an obvious decrease in reduction temperature and auto-reduction effect of CNTs, and the restriction effect of CNTs on growth of LDO nanoparticles lead to a rise in their specific surface area. As mentioned above, the changes in structure and properties of LDOs loaded inside CNTs facilitate conversion of syngas into higher alcohols. Moreover, CNTs with small inner size show stronger confinement effect.

Visualizing the Birth and Monitoring the Life of a Bimetallic Methanation Catalyst.

Well-defined bimetallic heterogeneous catalysts are not only difficult to synthesize in a controlled manner, but their elemental distributions are also notoriously challenging to define. Knowledge of these distributions is required for both the as-synthesized catalyst and its activated form under reaction conditions, where various types of reconstruction can occur. Success in this endeavor requires observation of the active catalyst via in situ analytical methods. As a step toward this goal, we present a composite material composed of bimetallic nickel-ruthenium nanoparticles supported on a protonated zeolite (Ni-Ru/HZSM-5) and probe its evolution and function as a photoactive carbon dioxide methanation catalyst using in situ X-ray absorption spectroscopy (XAS). The working Ni-Ru/HZSM-5, as a selective and durable photothermal CO2 methanation catalyst, comprises a corona of Ru nanoparticles decorating a Ni nanoparticle core. The specific Ni-Ru interactions in the bimetallic particles were confirmed by in situ XAS, which reveals significant electron transfer from Ni to Ru. The light-harvesting Ni nanoparticle core and electron-accepting Ru nanoparticle corona serve as the CO2 and H2 dissociation centers, respectively. These Ni and Ru nanoparticles also promote synergistic photothermal and hydrogen atom transfer effects. Collectively, these effects enable an associative CO2 methanation reaction pathway while hindering coking and fostering high selectivity toward methane.

A CoFe Bimetallic Catalyst for the Direct Conversion of Syngas to Olefins

Syngas conversion is a useful technology for converting nonpetroleum carbon resources into chemicals such as olefins. Iron- and cobalt-based catalysts, as two major categories, have been extensively studied in Fischer–Tropsch synthesis to olefins (FTO) reactions. Although both iron and cobalt catalysts have shown distinct merits and shortcomings, they are also complementary in their properties and catalytic performances when combined with each other. Herein, Na-modified CoFe bimetallic catalysts were fabricated using a co-precipitation method. It was found that there was a synergistic effect between Co and Fe that promoted a CO dissociation rate and carburization, and an appropriate Co/Fe ratio was conducive to improvements in their catalytic performances. The desired olefins selectivity reached 66.1 C% at a CO conversion of 37.5% for a Co2Fe1 catalyst, while the methane selectivity was only 4.3 C%. In addition, no obvious deactivation was found after nearly 160 h, indicating their potential industrial application.

Micro kinetic analysis of the CO2 hydrate formation and dissociation with L-tryptophan in brine via high pressure in situ Raman spectroscopy for CO2 sequestration

Hydrate-based CO2 sequestration (HBCS) is widely recognized as a promising, long-term, and stable approach for CO2 sequestration, but its slow formation kinetics in saline systems pose a significant challenge. In order to address this challenge, this experimental study investigated the potential of L–Tryptophan (L–Trp) as a CO2 hydrate kinetic promoter in deionized water and brine systems. A high-pressure reactor coupled with in situ Raman spectroscopy was used to examine macro-level kinetics and micro-level Raman spectra. The CO2 hydrate formation experiments were conducted at 3.5 MPa and 275.15 K, with different L–Trp concentrations (0–3000 ppm) in deionized water (DI) and brine systems. Raman spectra were monitored throughout the hydrate formation process, identifying distinct peaks corresponding to dissolve CO2, CO2 hydrates, and water activity. The experimental results indicate that the addition of 1000 ppm L–Trp in deionized water significantly enhances CO2 uptake by 3.6–fold and promotes hydrate formation kinetics by 3.3–fold compared to the system without L–Trp. In the brine system (3.5 wt% NaCl), the optimal L–Trp concentration was found to be 2000 ppm, leading to a 1.5-fold increase in CO2 uptake. Remarkably, L–Trp not only enhances the formation kinetics but also facilitates dissociation and CO2 recovery in DI water. Nevertheless, the presence of NaCl hinders the promoting effect of L–Trp on the dissociation kinetics. These findings represent a significant advancement in feasible HBCS technology for CO2 sequestration.

Ni-noble metal bimetallic catalysts for improved low temperature CO2 methanation

Bimetallic nickel-noble metal catalysts with low noble metal load (1 wt% of Ru, Pt, Rh, Pd, orIr) supported on Pr-doped CeO2 were comparatively evaluated regarding their CO2 methanation catalytic performance. Ru was the sole noble metal phase that could dramatically promote the catalytic activity of the corresponding monometallic catalyst, whereas the incorporation of the other noble metals either retained (Pt and Ir) or worsened (Rh and Pd) the catalytic performance. The best–performing RuNi bimetallic catalyst maintained around 80 % CO2 conversion and 99.5 % CH4 selectivity at 325 °C during 50 h of operation. Ru was found to be well dispersed along the support (as single atoms or small clusters), while a small part of it was also dispersed atop the medium-sized Ni nanoparticles. Its promoting ability was attributed to the improved metal dispersion, catalyst reducibility, moderate basicity and provision of additional active sites for CO2 and H2 dissociation, while DFT analysis evidenced that a Ru single atom atop a Ni cluster/ small particle is the structure that is most favorable towards the initial CO2 adsorption and dissociation.

High-dispersed CeOx species on mesopores silica to accelerate Ni-catalysed CO2 methanation at low temperatures

CO2 methanation is a key step in the power-to-gas technology for storing and distributing renewable energy as energy vectors. Due to thermodynamic constraints, highly active catalysts below about 300 °C are necessary. We demonstrate that their preparation is possible by supporting Ni nanoparticles over highly dispersed CeOx species decorating mesopores silicate (mSiO2) obtained by a template-free method. The CeOx decorated mSiO2 exhibits a 3-fold increase in activity and enhanced CH4 selectivity (98.7 % at 300 °C) compared to the Ni/mSiO2 catalyst. The performances are superior compared to the literature data. A systematic characterisation by physisorption, XPS, XAFS, UV–Vis and HR-TEM shows a uniform dispersion of highly dispersed CeOx within the mesoporous silica framework. The CO2 hydrogenation properties were investigated in a fixed-bed flow reactor and complemented by CO2-TPD, CO2-TPSR, in-situ FTIR, and D2 kinetic isotope experiments. The results show that highly dispersed CeOx exhibits excellent CO2 adsorption and dissociation abilities. The inverse kinetic isotope effect indicates that CO2 activation is the rate-determining step of the reaction. CO2 is strongly adsorbed on CeOx to form bidentate carbonate, which accelerates the generation of CO while avoiding the adsorption of CO2 on Ni nanoparticles.