How bulk and surface properties of Ti4SiC3, V4SiC3, Nb4SiC3 and Zr4SiC3 tune reactivity: a computational study

Recent Advances in Carbon Dioxide Adsorption, Activation and Hydrogenation to Methanol using Transition Metal Carbides

The inevitable emission of carbon dioxide (CO₂ ) due to the burning of a substantial amount of fossil fuels has led to serious energy and environmental challenges. Metal-based catalytic CO₂ transformations into commodity chemicals are a favorable approach in the CO₂ mitigation strategy. Among these transformations, selective hydrogenation of CO₂ to methanol is the most promising process that not only fulfils the energy demands but also re-balances the carbon cycle. The investigation of CO₂ adsorption on the surface of heterogeneous catalyst is highly important because the formation of various intermediates which determines the selectivity of product. Transition metal carbides (TMCs) have received considerable attention in recent years because of their noble metal-like reactivity, ceramic-like properties, high chemical and thermal stability. These features make them excellent catalytic materials for a variety of transformations such as CO₂ adsorption and its conversion into value-added chemicals. Herein, the catalytic properties of TMCs are summarize along with synthetic methods, CO₂ binding modes, mechanistic studies, effects of dopant on CO₂ adsorption, and carbon/metal ratio in the CO₂ hydrogenation reaction to methanol using computational as well as experimental studies. Additionally, this Review provides an outline of the challenges and opportunities for the development of potential TMCs in CO₂ hydrogenation reactions.

A first-principles study of CO2 hydrogenation on Niobium-terminated NbC (111) surface

As a promising material for the reduction of Greenhouse gas, 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 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 HCOOH * dissociation reaction (2.004eV). The preferred mechanism of CO2 hydrogenation towards CH 4 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 CH3 OH 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. It is also found from the electronic properties calculations that Nb-terminated NbC (111) is a suitable catalyst for CO2 hydrogenation where adsorption and activation of CO2 and also desorption of final products can be easily done on the surface.