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 Review of Theoretical Studies on Carbon Monoxide Hydrogenation via Fischer–Tropsch Synthesis over Transition Metals

The increasing demand for clean fuels and sustainable products has attracted much interest in the development of active and selective catalysts for CO conversion to desirable products. This review maps the theoretical progress of the different facets of most commercial catalysts, including Co, Fe, Ni, Rh, and Ru. All relevant elementary steps involving CO dissociation and hydrogenation and their dependence on surface structure, surface coverage, temperature, and pressure are considered. The dominant Fischer–Tropsch synthesis mechanism is also explored, including the sensitivity to the structure of H-assisted CO dissociation and direct CO dissociation. Low-coordinated step sites are shown to enhance catalytic activity and suppress methane formation. The hydrogen adsorption and CO dissociation mechanisms are highly dependent on the surface coverage, in which hydrogen adsorption increases, and the CO insertion mechanism becomes more favorable at high coverages. It is revealed that the chain-growth probability and product selectivity are affected by the type of catalyst and its structure as well as the applied temperature and pressure

Experimental and density functional theory studies of laminar double-oxidized graphene oxide nanofiltration membranes

The type and loading level of oxygen-containing functional groups on graphene oxide (GO) nanosheets significantly affect the size and alignment of nanochannels formed between the GO nanosheets and the separation performance of laminar GO membranes. Here, we demonstrate how double-oxidation of GO leads to the higher surface charge of GO nanosheets, the formation of highly stable water-based GO solution, more-ordered deposition of GOs on the polyethersulfone membrane through the pressure-assisted self-assembly method, and the formation of highly durable GO membranes possessing smoother surface morphology and higher antifouling properties. A multi-technique investigation was applied to follow the physicochemical difference between GO and double-oxidized GO, and the physical stability and separation performance of the corresponding membranes using experimental and computational studies. The double-oxidized GO-based membranes provided a significantly high water flux of 230 L/(m2.h) in 2.5 bar transmembrane pressure, excellent rejection of 99.9% for methylene blue (MB) dye, and outstanding separation performance stability over time. In contrast, GO membranes showed rejection of 81.5% for MB, and their separation performance diminished significantly over time. The antifouling properties of double-oxidized GO membranes were substantially higher (∼ four times) due to their higher negative surface charge and smoother surface morphology. The density functional theory (DFT) was used to gain insight into the interactions between the functional groups and the reasoning for the higher mechanical stability of double-oxidized GO membranes. Results revealed that the formation energy of GO decreases by increasing the number density of functional groups. It was also found that a higher number of carboxyl groups at the edges of the double-oxidized GO leads to higher hydrogen bonding, higher binding energy, and a more stable GO-membrane structure.</p

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

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

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 novel smart framework for sustainable nanocomposite electrolytes based on ionic liquids of dye-sensitized solar cells by a covalently multifunctional graphene oxide-vinyl imidazole/4-tert-butylpyridine cobalt complex

In this study, covalently multifunctional graphene oxide (GO) with vinyl imidazole/4-tert-butylpyridine cobalt complex (GO-VI/TBP cobalt complex) was synthesized through a novel approach. To this end, GO was functionalized with 1-vinyl imidazole (VI), followed by establishing a reaction between GO-VI, 4-tert-butylpyridine (TBP), and anhydrous CoCl2. Then, in dye-sensitized solar cells (DSSCs), this synthesized compound was used as an effective additive in sustainable nanocomposite electrolytes based on 1-butyl-3-methylimidazolium iodide (BMII) and 1-ethyl-3-methylimidazolium iodide (EMII) ionic liquids (ILs). Adding 0.6 wt% of optimal GO-VI/TBP cobalt complex to electrolyte increased the conversion efficiency of DSSCs significantly up to 7.359 % compared to 4.130 % in the initial standard DSSCs. This 78.18 % efficiency increase demonstrates how the GO-VI/TBP cobalt complex as a molecular bridge affects the conductivity and electron transport in the electrolyte based on ionic liquids. By enhancing the I-/I3 - diffusion coefficient, cobalt complexes with the TBP ligand and nitrogen-containing heterocyclic compounds in GO-VI/TBP cobalt complex compounds accelerated electron transfers and ion conductivity in the electrolyte. As a result, the short circuit current density (Jsc) increased from 8.131 to 14.301 mA cm−2, and the open-circuit voltage (VOC) rose from 0.725 to 0.754 V. Density functional theory (DFT) studies showed an increase in the conduction band of the TiO2 electrode after the adsorption of the electrolyte additives on its surface. This upward shift resulted in the quick injection of electrons from the dye’s lowest unoccupied molecular orbital (LUMO) to the TiO2 electrode’s conduction band. Finally, a soft computing system was designed to predict experimental features (VOC and JSC) based on effective factors. Based on the results, Random Tree, Random Forest, and Multilayer Perceptron (MLP) methods with correlation coefficients greater than 0.92 have the highest efficiency for creating the soft sensor. Overall, this work can be employed as a novel strategy for advancing the usage of graphene derivatives in this sector to boost the performance of electrolytes