CO 2 Reduction to Methanol on CeO 2 (110) Surface: a Density Functional Theory Study

Unveiling the Structure of Oxygen Vacancies in Bulk Ceria and the Physical Mechanisms behind Their Formation

Understanding the structures of oxygen vacancies in bulk ceria is crucial as they significantly impact the material's catalytic and electronic properties. The complex interaction between oxygen vacancies and Ce3+ ions presents challenges in characterizing ceria's defect chemistry. We introduced a machine learning-assisted cluster-expansion model to predict the energetics of defective configurations accurately within bulk ceria. This model effectively samples configurational spaces, detailing oxygen vacancy structures across different temperatures and concentrations. At lower temperatures, vacancies tend to cluster, mediated by Ce3+ ions and electrostatic repulsion, while at higher temperatures, they distribute uniformly due to configurational entropy. Our analysis also reveals a correlation between thermodynamic stability and the band gap between occupied O 2p and unoccupied Ce 4f orbitals, with wider band gaps indicating higher stability. This work enhances our understanding of defect chemistry in oxide materials and lays the groundwork for further research into how these structural properties affect ceria's performance.

Exploiting phase transitions in catalysis: reaction ofCO2andH2on dopedVO2-polymorphs

VO2is well known for its reversible transition between two phases with tetragonal rutile and monoclinic structure. In a previous theoretical study (Stahl and Bredow 2022ChemPhysChem23e202200131) we showed that the adsorption energy of CO is different on surfaces of the two Mo-stabilized polymorphs. This can be exploited to promote catalytic reactions by removing CO from the catalyst surface. As proof-of-principle, we investigated the hydrogenation reaction ofCO2. For this purpose, the adsorption energies ofCO2and possible intermediates and productsH2O, HCOOH,H2COand CO were calculated. Significant differences were found for the reaction energies of the hydrogenation ofCO2to formic acid and formaldehyde on the two polymorphs. This shows that it is in principle possible to alter the reaction thermodynamics by applying reaction conditions which stabilize a particular polymorph. In order to investigate the influence of the polymorph on kinetic properties, the reactions barriers of a step-wise reaction ofCO2+2H2→H2CO+H2Owas calculated using the nudged elastic band method.VO2was found to reduce the reaction barriers compared to the gas phase. Additionally, the minimum energy path of the bulk phase transition of undopedVO2was calculated using the distinguished reaction coordinate method. A catalytic cycle exploiting the phase transition is proposed based on the theoretical results.

Plasma-catalysis for VOCs decomposition: A review on micro- and macroscopic modeling

Plasma-catalysis has been recognized as a promising method to decompose hazardous volatile organic compounds (VOCs) since many years ago. To understand the fundamental mechanisms of VOCs decomposition by plasma-catalysis systems, both experimental and modeling studies have been extensively carried out. However, literature on summarized modeling methodologies is still scarce. In this short review, we therefore present a comprehensive overview of modeling methodologies ranging from microscopic to macroscopic modeling in plasma-catalysis for VOCs decomposition. The modeling methods of VOCs decomposition by plasma and plasma-catalysis are classified and summarized. The roles of plasma and plasma-catalyst interactions in VOCs decomposition are also critically examined. Taking the current advances in understanding the decomposition mechanisms of VOCs into account, we finally provide our perspectives for future research directions. This short review aims to stimulate the further development of plasma-catalysis for VOCs decomposition in both fundamental studies and practical applications with advanced modeling methods.

The inchoate horizon of electrolyzer designs, membranes and catalysts towards highly efficient electrochemical reduction of CO2 to formic acid

This review explores the recent advances in CO2 reactor configurations, components, membranes and electrocatalysts for HCOOH generation and draw readers attention to construct the economic, scalable and energy efficient CO2R electrolyzers.

DFT insights into electrocatalytic CO2 reduction to methanol on α-Fe2O3(0001) surfaces

Electrocatalytic reduction of CO₂ to manufacture fuels and other useful chemicals is one of the appealing methods to reuse CO₂. Herein, electrocatalytic CO₂ reduction on a model α-Fe₂O₃(0001) surface catalyst has been investigated by means of density functional theory. This systematic study, involving 20 reaction intermediates and 63 distinct elementary reaction steps, has allowed the identification of a novel mechanism for the decomposition of the key intermediate *COOH. Methanol is the preferred product, with an overpotential of 0.8 V, over carbon monoxide (CO), formic acid (HCOOH), and formaldehyde (CH₂O). Formaldehyde formed on the surface will be converted into methanol. This work demonstrates the need for a complete investigation of possible pathways to find the most favourable one, beyond chemical intuition. Moreover, it suggests that hematite could be an interesting material for CO₂ reduction.

CO2 Reduction by Hydrogen Pre-Reduced Acceptor-Doped Ceria

The reactivity of H₂ pre-reduced acceptor-doped ceria materials Gd_0.10 Ce_0.90 O_2-δ (GDC10) and Sm_0.15 Ce_0.85 O_2-δ (SDC15) was tested with respect to the reduction of CO₂ to CO in the context of the reverse water-gas shift reaction. It was demonstrated that not only oxygen vacancies, but also dissolved hydrogen is a reactive species for the reduction of CO₂ . Dissolved hydrogen must be considered upon discussion of the mechanism of the reverse water-gas shift reaction on ceria-derived materials apart from oxygen vacancies and formates. The reduction of CO₂ is preceded by the formation of carbonate species of different thermal stability and reactivity. The stability of these carbonates was directly demonstrated by in situ infrared spectroscopy and revealed the largely reversible nature of CO₂ ad- and desorption. In comparison to pre-reduced samples, decreased carbonate coverage is obtained after oxidative treatments of GDC10 and SDC15. No significant effect of the sample treatment (O₂ oxidation or H₂ reduction) on the surface carbonate stability was noticed. Mono-dentate carbonates and carboxylates appear to be more easily formed on pre-reduced (i. e. defective) samples. Ce⁴⁺ reduction to Ce³⁺ (by H₂ ) and re-oxidation to Ce⁴⁺ (by CO₂ ) on GDC10/SDC15 were directly monitored by infrared spectroscopic analysis of a distinct, IR-active electronic transition of Ce³⁺ . These results show the complex interplay of oxygen vacancy/dissolved hydrogen reactivity and surface chemical aspects in acceptor-doped ceria materials.

Ceria-Based Materials in Hydrogenation and Reforming Reactions for CO2 Valorization

Reducing greenhouse emissions is of vital importance to tackle the climate changes and to decrease the carbon footprint of modern societies. Today there are several technologies that can be applied for this goal and especially there is a growing interest in all the processes dedicated to manage CO2 emissions. CO2 can be captured, stored or reused as carbon source to produce chemicals and fuels through catalytic technologies. This study reviews the use of ceria based catalysts in some important CO2 valorization processes such as the methanation reaction and methane dry-reforming. We analyzed the state of the art with the aim of highlighting the distinctive role of ceria in these reactions. The presence of cerium based oxides generally allows to obtain a strong metal-support interaction with beneficial effects on the dispersion of active metal phases, on the selectivity and durability of the catalysts. Moreover, it introduces different functionalities such as redox and acid-base centers offering versatility of approaches in designing and engineering more powerful formulations for the catalytic valorization of CO2 to fuels.

Design of iron atom modified thiophene-linked metalloporphyrin 2D conjugated microporous polymer as CO2 reduction photocatalyst

We designed a series of 2D CMPs and found that the Fe-CMPs possess the highest catalytic activity toward CO₂ photoreduction.

DFT insights into oxygen vacancy formation and CH4 activation over CeO2 surfaces modified by transition metals (Fe, Co and Ni)

The effects of transition metal (Fe, Co and Ni) modification (adsorption, insertion and substitution) of CeO₂ surfaces on oxygen vacancy formation and CH₄ activation are studied on the basis of first principles calculations.

Synthesis of methanol from CO2hydrogenation promoted by dissociative adsorption of hydrogen on a Ga3Ni5(221) surface

The presence of Ga promotes H₂dissociation adsorption, and subsequently improves the process of CO₂hydrogenation to CH₃OH.

Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide

In view of the climate changes caused by the continuously rising levels of atmospheric CO2 , advanced technologies associated with CO2 conversion are highly desirable. In recent decades, electrochemical reduction of CO2 has been extensively studied since it can reduce CO2 to value-added chemicals and fuels. Considering the sluggish reaction kinetics of the CO2 molecule, efficient and robust electrocatalysts are required to promote this conversion reaction. Here, recent progress and opportunities in inorganic heterogeneous electrocatalysts for CO2 reduction are discussed, from the viewpoint of both experimental and computational aspects. Based on elemental composition, the inorganic catalysts presented here are classified into four groups: metals, transition-metal oxides, transition-metal chalcogenides, and carbon-based materials. However, despite encouraging accomplishments made in this area, substantial advances in CO2 electrolysis are still needed to meet the criteria for practical applications. Therefore, in the last part, several promising strategies, including surface engineering, chemical modification, nanostructured catalysts, and composite materials, are proposed to facilitate the future development of CO2 electroreduction.