Computational Study of Zn Single-Atom Catalysts on In₂O₃ Nanomaterials for Direct Synthesis of Acetic Acid from CH₄ and CO₂

Abstract

The direct conversion of methane and carbon dioxide will be a promising way to alleviate the greenhouse gas effect and reduce the dependency on traditional fossil fuels. In this study, the catalytic transformation of methane and carbon dioxide to acetic acid with a 100% atomic economy effect over the zinc single-atom catalyst supported on In2O3 nanomaterial with surface oxygen vacancy (Zn1/In2O3–x ) was investigated by using density functional theory calculations, including dissociative adsorption of methane, C–C bond coupling, acetate species protonation, and desorption of acetic acid. The results indicate that the Zn single atom is beneficial to the dissociation of methane and the stabilization of methyl by forming the Zn–CH3 species. Besides, carbon dioxide can be adsorbed on the surface of the catalyst and activated further owing to the presence of surface oxygen vacancy. The facile C–C coupling of co-adsorbed methyl and carbon dioxide is realized by the synergistic mode combining the Zn single atom and surface oxygen vacancy following the Langmuir–Hinshelwood mechanism, in which a Zn–C–C moiety is formed in the transition state. The subsequently formed acetate species is bonded with Zn strongly and undergoes a protonation process to form acetic acid which also interacts strongly with the Zn single atom, resulting in desorption of acetic acid being the rate-determining step of the whole reaction. The insights in this work would be useful to clarify the reaction mechanism of producing acetic acid from methane and carbon dioxide over the Zn1/In2O3–x single-atom catalyst, which could provide a sufficient way to design efficient catalysts for methane and carbon dioxide conversion.

Exploration of the active sites on a Rh–In2O3 catalyst for the semi-hydrogenation of acetylene: a theoretical study

“…For C 2 H 2 adsorption, the overlap of Rh 4d and C 2p orbitals results from the bond formation between C 2 H 2 and the active site. 29,48 In accordance with the results of adsorption energy, the supported Rh 4 site shows the most overlap among these three sites with the lowest adsorption energy. The total charge of activated C 2 H 2 on the supported Rh 4 site is −0.11 |e|, which indicates the strong electron transfer from the metal site to absorbate.…”

“…7,[26][27][28] Furthermore, oxygen vacancies over indium oxide with the modification by single atoms show unique properties compared with pristine oxygen vacancies. For example, Zhou et al 29 suggested that the oxygen vacancy with a Zn single atom over the In 2 O 3 (111) facet is active for the synthesis of acetic acid from CH 4 and CO 2 . The presence of Zn single atoms not only facilitates the formation of Zn-CH 3 species but also regulates the properties of the oxygen vacancy.…”

Acetic Acid Production from CH4 and CO2 via Synergistic Catalysis between Pd Particles and Oxygen Vacancies Generated in ZrO2

“…Then, the dissociation of CH 4 occurs on the Pd 10 cluster to create CH 3 * and H* with a barrier of only 0.81 eV. It is lower than the barriers reported in previous catalytic systems for the same reaction, such as Zn SAC (0.87 eV), Fe/ZnO (0.93 eV), CeO 2 -ZnO/MMT (0.97 eV), Au-ZSM-5 (1.41 eV), and sulfated zirconia (1.49 eV). ,,− The difference between the two pathways begins at the C–C coupling step. In path A, CH 3 * couples directly with CO 2 * into CH 3 COO* with a barrier of 1.65 eV.…”

Theoretical Study of Intermetallic Compound Nanoalloys for Direct Conversion of Methane to Methanol

“…Yoshizawa et al explored the reaction mechanism for the direct conversion of methane to methanol on the surface of Pd as well as Pd/Au catalysts, and showed that the weakly bound hydroxyl groups on Au sites in the Pd/Au alloys contribute to the C–H bond cleavage process and are able to reduce the methane activation energy barrier (to 14.7 kcal/mol) . Besides, alloy catalysts such as single-atom alloys (SAA) and high-entropy alloys (HEA) can be tuned to achieve better catalytic performance by modulating the systematic size of the active sites. − However, in disordered alloys, multiple types of adsorption sites can lead to the formation of local segregation, thus inhibiting catalyst confinement …”