Thermodynamic and Kinetic Study of Carbon Dioxide Hydrogenation on the Metal-Terminated Tantalum-Carbide (111) Surface: A DFT Calculation

The need to reduce our reliance on fossil fuels and lessen the environmentally harmful effects of CO2 have encouraged investigations into CO2 hydrogenation to produce useful products. Transition metal carbides exhibit a high propensity towards CO2 activation, which makes them promising candidates as suitable catalysts for CO2 hydrogenation. Here, we have employed calculations based on the density-functional theory to investigate the reaction network for CO2 hydrogenation to product molecules on the tantalum-terminated TaC (111) surface, including two routes from either HCOOH* or HOCOH* intermediates. Detailed calculations of the reaction energies and energy barriers along multiple potential catalytic pathways, along with the exploration of all intermediates, have shown that CH4 is the predominant product yielded through a mechanism involving HCOOH, with a total exothermic reaction energy of −4.24 eV, and energy barriers between intermediates ranging from 0.126 eV to 2.224 eV. Other favorable products are CO and CH3OH, which are also produced via the HCOOH pathway, with total overall reaction energies of −2.55 and −2.10 eV, respectively. Our calculated thermodynamic and kinetic mechanisms that have identified these three predominant products of the CO2 hydrogenation catalyzed by the TaC (111) surface explain our experimental findings, in which methane, carbon monoxide, and methanol have been observed as the major reaction products

A First-Principles Study of CO2 Hydrogenation on a Niobium-Terminated NbC (111) Surface

Density functional theory calculations are used to investigate the electronic properties and catalytic activity of an Nb-terminated NbC (111) surface towards CO2 hydrogenation to gain insight into the mechanisms related to CO2 hydrogenation to other products. The results show that the formations of CH4, CH3OH, and CO are favored in comparison to other compounds, with CH4 being the dominant product. In addition, the reaction energies reveal that the preferred mechanism for CO2 hydrogenation is thorough HCOOH. As promising materials for the reduction of greenhouse gases, transition-metal carbides, which are highly active in the hydrogenation of CO2, are mainly considered. In this regard, the reaction mechanism of CO2 hydrogenation to useful products on the Nb-terminated NbC (111) surface is investigated by applying density functional theory calculations. The computational results display that the formation of CH4, CH3OH, and CO are more favored than other compounds, where CH4 is the dominant product. In addition, the findings from reaction energies reveal that the preferred mechanism for CO2 hydrogenation is thorough HCOOH*, where the largest exothermic reaction energy releases during the HCOOH* dissociation reaction (2.004 eV). The preferred mechanism of CO2 hydrogenation towards CH4 production is CO2*→t,c-COOH*→HCOOH*→HCO*→CH2O*→CH2OH*→CH2*→CH3*→CH4*, where CO2*→t,c-COOH*→HCOOH*→HCO*→CH2O*→CH2OH*→CH3OH* and CO2*→t,c-COOH*→CO* are also found as the favored mechanisms for CH3OH and CO productions thermodynamically, respectively. During the mentioned mechanisms, the hydrogenation of CH2O* to CH2OH* has the largest endothermic reaction energy of 1.344 eV

A density functional theory study of CO2 hydrogenation on carbon-terminated TaC (111) surface

In this study, the density functional theory implemented in the Vienna ab initio simulation package was used to shed more light on the catalytic Carbon dioxide (CO2) hydrogenation process on the (111) facet of the carbon-terminated tantalum carbide (TaC) surface. The adsorption of several intermediates and their hydrogenation elementary steps on the TaC (111) surface towards the formation and desorption of the main products including carbon monoxide (CO), methane (CH4), and methanol (CH3OH) was investigated. The results indicate that the involved intermediates adsorb strongly to the carbon-terminated TaC (111) surface by releasing large energies. The calculated reaction energies concluded in proposing the preferred mechanisms energetically, where the found pathways are overall endothermic which can be provided by the large exothermic adsorption energies of the intermediates. The favorite routes to the formation of desired compounds including CO, CH4, and CH3OH require overall reaction energies of 1.29, 5.96, and 6.63 eV, where they go through dihydroxycarbene (HOCOH) intermediate created from t-COOH hydrogenation. Along these routes, COH dehydrogenation to CO releases the largest exothermic reaction energy of − 2.30 eV, while hydrogenation of t-HCOH to CH2OH requires the highest endothermic reaction energy of 2.69 eV to proceed. It is concluded that CO and CH4 are the main products of CO2 hydrogenation on carbon terminated TaC (111) surface, in agreement with experimental and theoretical studies