Adsorption of Carbon Dioxide on Al12X Clusters Studied by Density Functional Theory: Effect of Charge and Doping

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Water and carbon dioxide adsorption at olivine surfaces

Influence of varying carbon oxides concentrations on the selectivity of an electrical sensor utilizing graphene nanoribbons

Molecular level investigation of methane and carbon dioxide adsorption on SiO2 surface

The transition states and activation barriers of the 1,3-dipolar cycloadditions of azides with cycloalkynes and cycloalkenes were explored using B3LYP density functional theory (DFT) and spin component scaled SCS-MP2 methods. A survey of benzyl azide cycloadditions to substituted cyclooctynes (OMe, Cl, F, CN) showed that fluorine substitution has the most dramatic effect on reactivity. Azide cycloadditions to 3-substituted cyclooctynes prefer 1,5-addition regiochemistry in the gas phase, but CPCM solvation abolishes the regioselectivity preference, in accord with experiments in solution. The activation energies for phenyl azide addition to cycloalkynes decrease considerably as the ring size is decreased (cyclononyne DeltaG(double dagger) = 29.2 kcal/mol, cyclohexyne DeltaG(double dagger) = 14.1 kcal/mol). The origin of this trend is explained by the distortion/interaction model. Cycloalkynes are predicted to be significantly more reactive dipolarophiles than cycloalkenes. The activation barriers for the cycloadditions of phenyl azide and picryl azide (2,4,6-trinitrophenyl azide) to five- through nine-membered cycloalkenes were also studied and compared to experiment. Picryl azide has considerably lower activation barriers than phenyl azide. Dissection of the transition state energies into distortion and interaction energies revealed that "strain-promoted" cycloalkyne and cycloalkene cycloaddition transition states must still pay an energetic penalty to achieve their transition state geometries, and the differences in reactivity are more closely related to differences in distortion energies than the amount of strain released in the product. Trans-cycloalkene dipolarophiles have much lower barriers than cis-cycloalkenes.

Ketenes are excellent precursors for catalytic asymmetric reactions, creating chiral centers mainly through addition across their C = C bonds. Density functional theory (DFT) calculations at the MO6/LACVP* and B3LYP/LACVP* levels of theory were employed in a systematic investigation of the peri-, chemo- and regio-selectivity of the addition of transition metal oxo complexes of the type ReO 3 L ( L = Cl -, O -, OCH 3, CH 3) to substituted ketenes O = C = C ( CH 3)(X) [ X = CH 3, H , CN , Ph ] with the aim of elucidating the effects of substituents on the mechanism of the reactions. The [2 + 2] addition pathway across the C = C or C = O (depending on the ligand) is the most preferred in the reactions of dimethyl ketene with all the metal complexes studied. The [2 + 2] pathway is also the most preferred in the reactions of ReO 3 Cl with all the substituted ketenes studied except when X = Cl . Thus of all the reactions studied, it is only the reaction of ReO 3 Cl with O = C = C ( CH 3)( Cl ) that prefers the [3 + 2] addition pathway. Reactions of dimethyl ketene with ReO 3 L favors addition across C = O bonds of the ketene when L = O - and CH 3 but favors addition across C = C bonds when L = OCH 3 and Cl . In the reactions of ReO 3 Cl with substituted ketenes, addition across C = O bonds is favored only when X = H while addition across C = C bonds is favored when X = CH 3, Cl , Ph , CN . The reactions of dimethyl ketene with ReO 3 L will most likely lead to the formation of an ester precursor in each case. A zwitterionic intermediate is formed in the reactions except in the reactions of [Formula: see text]. The order in the activation energies of the reactions of dimethyl ketenes with the metal complexes ReO 3 L with respect to changing ligand L is O - < CH 3 O - < Cl - < CH 3 while the order in reaction energies is CH 3 < CH 3 O - < O - < Cl -. For the reactions of substituted ketenes with ReO 3 Cl , the order in activation barriers is CH 3 < Ph < CN < Cl < H while the reaction energies follow the order Cl < CH 3 < H < Ph < CN . In the reactions of dimethyl ketenes with ReO 3 L , the trend in the selectivity of the reactions with respect to ligand L is Cl - < CH 3 O - < CH 3 < O - while the trend in selectivity is CH 3 < CN < Cl < Ph in the reactions of ReO 3 Cl with substituted ketenes. It is seen that reactions involving a change in oxidation state of metal from the reactant to product have high activation barriers while reactions that do not involve a change in oxidation state have low activation barriers. For both [3 + 2] and [2 + 2] additions, low activation barriers are obtained when the substituent on the ketene is electron-donating while high activation barriers are obtained when the substituent is electron-withdrawing.

The adsorption and activation of carbon dioxide over copper cluster (Cu4) and copper doped on the alumina support (Cu4/Al2O3) catalytic systems have been investigated by using density functional theory and climbing image nudged elastic band. The adsorption energies, geometrical configurations, and electronic properties are analysed. The results show the strong chemical interaction between the copper cluster and the alumina support. Both the Cu4 cluster and Cu4/Al2O3 systems have a high adsorption ability for CO2, and the adsorption process is of chemical nature. The role of the alumina support in the adsorption and activation of CO2 has been addressed. The calculated results show that the “synergistic effect” between Al2O3 and Cu4 is the key factor in the activation of CO2.

The mechanisms underlying the reaction between carbon monoxide (CO) and activated dioxygen on metal oxide substrates to produce CO2 remain poorly understood, particularly regarding the role of oxygen vacancies and the nature of the activated O2 adsorbate. In this study, we present experimental findings from infrared reflection-absorption spectroscopy on a model system of bulk monocrystalline CeO2(111). Contrary to expectations, exposing the reduced surface to dioxygen (O2) at 80 K does not yield activated oxygen species, such as superoxo or peroxo. Notably, in the presence of adsorbed CO, an unexpected low-temperature oxidation reaction occurs, consuming CO while oxidizing the CeO2 substrate. Since a direct reaction between impinging O2 and adsorbed CO is unlikely at these low temperatures, a novel mechanism is proposed. Extensive spin-polarized density functional theory (DFT) calculations reveal that oxygen vacancies play a critical role in this low-temperature CO oxidation. Initially located in the subsurface region (Vss), these vacancies migrate to the surface (Vs) via a concerted interaction with coadsorbed CO and O2, leading to O2 activation and the formation of superoxo or peroxo species. Detailed analysis identifies key reaction intermediates and quantifies their adsorption energies and activation barriers. Our findings suggest that the peroxo-mediated pathway, with its lower activation barrier, is more favorable for CO oxidation at low temperatures compared to the carbonate pathway. This study provides valuable insights into the dynamic role of subsurface oxygen vacancies in the activation of gaseous O2 and CO oxidation mechanisms on CeO2.

In the present study, we perform a comparative study on the oxidation mechanism of CO gas molecules on SnO2 (110), (101), and (100) surfaces. The optimized adsorption configurations show that the adsorption of CO molecules could occur similarly on the three SnO2 surfaces via two adsorption modes, physisorption of CO on the Sn5c site that is considered as the first step for CO oxidation, followed by CO chemisorption on the O2c site resulting in the formation of CO2 species. Based on the calculated adsorption energies and CO molecule diffusion on SnO2 surfaces, CO molecule adsorption on the (101) surface exhibits the highest adsorption energy and the lowest reaction barrier for CO oxidation compared to the widely considered (110) surface or the (100) surface. These findings are expected to have a major impact on improving sensing properties toward toxic gas by means of surface-orientation engineering.

CO2 Capture via Crystalline Hydrogen-Bonded Bicarbonate Dimers

Activation of carbon dioxide and carbon monoxide at aluminium surfaces

Density functional theory is used to study one of the most successful routes to the production of synthetic fuels, the conversion of methanol to gasoline (MTG process) with an acidic zeolite. With our calculations we have determined transition states and adsorption complexes of reactants, intermediates, and products as well as the corresponding activation barriers and adsorption energies of the numerous reactions involved in such a process. Brønsted acid catalyzed methanol dehydration to dimethyl ether is the first step of the MTG process. Two different mechanisms are possible. One proceeds via an associative interaction between two methanol molecules, generating directly dimethyl ether, while the other proceeds via a methoxy surface species intermediate. The presence of water lowers the activation barrier of the last mechanism by more than 50 kJ/mol. Our calculations suggest that ethanol and ethyl methyl ether are the first formed species with a C−C bond. Several different mechanisms for those reactions have been studied. The activation barriers involved in such reactions are of the order of 300 kJ/mol for both ethanol and ethyl methyl ether. Without coadsorbed water, the activation barriers are 60 kJ/mol higher. In a following step ethylene is formed from alcohol or ether. Those reactions are very fast due to a very low activation barrier. Trimethyloxonium, proposed to be an intermediate in the formation of ethyl methyl ether, can be excluded as an intermediate for the C−C bond formation. Although it can be formed, its further reaction to ethanol or ethyl methyl ether involves activation barriers that are over 80−150 kJ/mol higher than their formation directly from dimethyl ether and methanol. Reaction paths for the formation of methane and formaldehyde, which are observed in reactions for very low methanol coverages, have also been studied.

Photocatalytic Methane Conversion: Insight into the Mechanism of C(sp ³ )–H Bond Activation

We present density functional calculations of O2 and CO adsorption on an AlAu6 cluster. It is found that in the AlAu6 cluster the active sites would be first occupied by coming O2 rather than CO due to a more negative binding energy of the former. Furthermore, the catalytic mechanisms of CO oxidation in AlAu6 clusters, which are based on a single CO molecule and double CO molecules, are discussed. This investigation reveals that the reaction of a single CO molecule with the AlAu6O2 complex has the lowest activation barrier (0.27 eV), which is 0.51 eV lower than that of the pure Au 6 − cluster. For the AlAu6O2(CO)2 complex, due to the structural distortion of the AlAu6 cluster, the activation barrier of the determination rate is higher by 0.53 eV than that of the AlAu6O2CO complex, which shows that the cooperation effect of the second CO molecule can go against CO oxidation. For the Al@Au6O2(CO)2 complex, the activation barrier of the determination rate is lower by 0.07 eV than the path of one CO molecule, which demonstrates that the cooperation effect of the second CO molecule can prompt CO oxidation.

The adsorption of carbon dioxide on the surfaces of zinc oxide doped with cerium was studied. For this, a theoretical study was carried out using computational simulations based on density functional theory to determine possible improvements in photocatalytic activity. for the capture and dissociation of carbon dioxide. Calculations were performed using density functional theory within the Perdew-Burke-Ernzerhof generalized gradient approximation, also the Hubbard correction together with ultrasmooth atomic pseudopotentials and a basic plane wave implemented in the Quantum-ESPRESSO package. The doping concentration level considered in this work was 6.25%, among the results, the semiconducting character of zinc oxide was evident from the density of states calculations, it was also found that by adding cerium impurities to zinc oxide, the values of the lengths and angles of the bonds vary a little, this may be due to the small difference in covalent radius that the zinc atom has with respect to the cerium atom, consequently, changes occurred in the electronic properties that consist in intermediate states in the energy bandgap located around the Fermi energy. This may suggest that the cerium-doped zinc oxide system can probably absorb visible light, which could lead to possible improvements in the photocatalytic properties of the material. Furthermore, we found that by adding carbon dioxide to the cerium-doped zinc oxide surface, the carbon dioxide is activated and this could suggest the dissociation or reduction of this contaminant.