Mechanism Of CO2 Hydrogenation Research Articles

Catalyst-free CO2 hydrogenation with BH3NH3 in water: DFT mechanistic insights

Extensive DFT calculations show that BH3NH3 may transfer dihydrogen as separated hydride and proton to CO2 rather than HCO3- in water over a barrier of 25.9 kcal mol-1, followed by faster hydride transfer from borate anions to either electrophilic CO2 or protic H2O or HCO2H, leading to competitive formate production and H2 release.

New mechanism insight for the hydrogenation of CO/CO2 gas mixtures to hydrocarbons over iron-based catalyst

Iron-based catalysts are the most suitable candidates for converting CO2 or CO2-rich syngas to hydrocarbons. However, several issues about the mechanism of CO2 hydrogenation are still unclear. In this work, we investigated the performance of an iron-based catalyst with H2/CO2, H2/CO/N2 and H2/CO/13CO2/N2 gas mixtures at the same process conditions (T = 270°C, P = 175 psi and SV = 3 NL/h/gcat). The CO2 hydrogenation rate was much lower than that observed for CO hydrogenation. 13CO2 tracer experiments indicated that CO2 is hydrogenated to hydrocarbons via the reverse water-gas shift even when present in small concentration (1.8 vol%). 13C enrichment was observed in both CO and C1-C4 hydrocarbons.

DFT study of CO2 catalytic conversion by H2 over Ni13 cluster

Understanding the mechanism and selectivity of CO2 catalytic conversion by H2 on a specific catalyst is of great significance in the context of renewable energy storage from a societal and technological point of view. In this paper, based on the density functional theory calculations, the possible reaction networks of CO2 hydrogenation on the Ni13 cluster are studied systematically. The adsorption energies of the reaction intermediates at various possible adsorption sites, the reaction energies and the activation energies of each elementary reaction are calculated. The results suggest that the adsorption properties of the CO2 and the intermediates on the Ni13 cluster are different from the specific crystal plane such as Ni(111) surface, and the intermediates are highly activated on the Ni13 surface. The most advantageous pathways for the production of HCOOH, CH3OH, and CH4 are determined, and the activation barrier of the corresponding rate-determining step is 1.63 eV, 1.55 eV, and 1.55 eV, respectively. This indicates that the Ni13 cluster has higher activity towards CO2 catalytic conversion compared with other catalysts such as Cu(111), Ni(111), and Pt/Ni(111) surface. Furthermore, the H3CO* hydrogenation or the dissociation is demonstrated to be the crucial step in determining the selectivity for CH3OH and CH4. The mechanism of CO2 hydrogenation on Ni13 cluster was determined by density functional theory calculation.

DFT Study of Catalytic CO2Hydrogenation over Pt-Decorated Carbon Nanocones: H2Dissociation Combined with the Spillover Mechanism

In this work, we investigate the catalytic role of platinum-decorated defective CNC (Pt/dCNC) in CO2 hydrogenation to formic acid (FA) by a density functional theory (DFT) approach. The reaction follows the equation CO2(g) + H2(g) → HCOOH(g). Combining highly reactive Pt atoms with defective CNC provides Pt/dCNC, a reactive monodispersed atomic catalyst for CO2 hydrogenation. We propose our new mechanism of CO2 hydrogenation over the Pt/dCNC catalyst involving a H2 dissociation and H spillover sequence that is energetically favorable. The rate-determining step is formic acid desorption that requires an energy barrier of 1.11 eV. Furthermore, our findings show that the rate of FA production is dependent on H2 concentration. Altogether, the theoretical results support the concept of the spillover mechanism, playing a key role in promoting CO2 hydrogenation via a formate intermediate. These results improve our understanding of the mechanism involving H2 dissociation with the H spillover process and the catal...

Metal-ligand bifunctional based Mn-catalysts for CO2 hydrogenation reaction

A series of monoligated bidentate aminophosphine (PN) based Noyori-type bifunctional Mn(I)-complexes has been studied for CO2 hydrogenation. The NH functionality of the PN ligand shows a metal–ligand cooperation (MLC) mechanism for CO2 hydrogenation. We show here that it is not essential for a NH functionality to show cooperation via cleavage/formation of NH bond as reported in the case of classical Noyori mechanism for ketone hydrogenation. Rather than this, the NH functionality can work as a chemically innocent ligand for stabilizing the formate anion via NH⋯O hydrogen bonding. More importantly, such stabilized formate anion favours the heterolytic H2 cleavage, which is otherwise a rate determining step. Furthermore, we show that the NH functionality plays a key role for such metal–ligand cooperation mechanism. Therefore, present study will provide an exclusive feature of chemically innocent cooperation in bifunctional catalysts for the development of more efficient catalysts design for CO2 hydrogenation reaction.

Making a Splash in Homogeneous CO2 Hydrogenation: Elucidating the Impact of Solvent on Catalytic Mechanisms.

Molecular catalysts for hydrogenation of CO2 are widely studied as a means of chemical hydrogen storage. Catalysts are traditionally designed from the perspective of controlling the ligands bound to the metal. In recent years, studies have shown that the solvent can also play a key role in the mechanism of CO2 hydrogenation. A prominent example is the impact of the solvent on the thermodynamic hydride donor ability, or hydricity, of metal hydride complexes relative to the hydride acceptor ability of CO2 . In some cases, simply changing from an organic solvent to water can reverse the direction of hydride transfer between a metal hydride and CO2 . Additionally, the solvent can impact catalysis by converting CO2 into carbonate species, as well as activate intermediate products for hydrogenation to more reduced products. By understanding the substrate and product speciation, as well as the reactivity of the catalyst towards the substrate, the solvent can be used as a central design component for the rational development of new catalytic systems.

Formation of Gas-Phase Formate in Thermal Reactions of Carbon Dioxide with Diatomic Iron Hydride Anions.

The hydrogenation of carbon dioxide involves the activation of the thermodynamically very stable molecule CO2 and formation of a C-H bond. Herein, we report that HCO2- and CO can be formed in the thermal reaction of CO2 with a diatomic metal hydride species, FeH- . The FeH- anions were produced by laser ablation, and the reaction with CO2 was analyzed by mass spectrometry and quantum-chemical calculations. Gas-phase HCO2- was observed directly as a product, and its formation was predicted to proceed by facile hydride transfer. The mechanism of CO2 hydrogenation in this gas-phase study parallels similar behavior of a condensed-phase iron catalyst.

Formation of Gas‐Phase Formate in Thermal Reactions of Carbon Dioxide with Diatomic Iron Hydride Anions

AbstractThe hydrogenation of carbon dioxide involves the activation of the thermodynamically very stable molecule CO2 and formation of a C−H bond. Herein, we report that HCO2− and CO can be formed in the thermal reaction of CO2 with a diatomic metal hydride species, FeH−. The FeH− anions were produced by laser ablation, and the reaction with CO2 was analyzed by mass spectrometry and quantum‐chemical calculations. Gas‐phase HCO2− was observed directly as a product, and its formation was predicted to proceed by facile hydride transfer. The mechanism of CO2 hydrogenation in this gas‐phase study parallels similar behavior of a condensed‐phase iron catalyst.

Carbon dioxide hydrogenation to aromatic hydrocarbons by using an iron/iron oxide nanocatalyst.

The quest for renewable and cleaner energy sources to meet the rapid population and economic growth is more urgent than ever before. Being the most abundant carbon source in the atmosphere of Earth, CO2 can be used as an inexpensive C1 building block in the synthesis of aromatic fuels for internal combustion engines. We designed a process capable of synthesizing benzene, toluene, xylenes and mesitylene from CO2 and H2 at modest temperatures (T = 380 to 540 °C) employing Fe/Fe3O4 nanoparticles as catalyst. The synthesis of the catalyst and the mechanism of CO2-hydrogenation will be discussed, as well as further applications of Fe/Fe3O4 nanoparticles in catalysis.

Chemisorption and catalysis by metal clusters. Hydrogenation of carbon monoxide and carbon dioxide catalysed by supported Ruthenium clusters derived from Ru3(CO)12 and from H4Ru4(CO)12

Properties are described for catalysts containing active clusters derived from Ru3(CO)12 and H4Ru4(CO)12 and supported on silica, alumina and titania. The clusters, protected against sintering by retained ligand-CO, ligand-C and a support–cluster interaction, are stable under the range of reaction conditions used (0.10 MPa, 444–635 K) and provide highly reproducible activity for the hydrogenation of carbon monoxide and carbon dioxide. Freshly prepared catalysts each exhibit an initial non-steady state, during which carbon is progressively retained and activity rises, passes through a maximum and declines to a steady state value. Catalysts in the steady state generally exhibited low activity for carbon monoxide hydrogenation. An effect of support on activity was observed such that as the strength of the metal-support interaction increases, the turnover frequency decreases. Carbon-14 tracer studies revealed differences in the mechanism of CO and CO2 hydrogenation and a detailed mechanism for CO2 hydrogenation is presented.