Mechanistic Insight into the Modification of the Surface Stability of In2O3 Catalyst Through Metal Oxide Doping

Effect of Conversion, Temperature and Feed Ratio on In2 O3 /In(OH)3 Phase Transitions in Methanol Synthesis Catalysts: A Combined Experimental and Computational Study

Catalytic hydrogenation of CO2 to methanol has attracted lots of attention as it makes CO2 useable as a sustainable carbon source. This study combines theoretical calculations based on the dummy catalytic cycle model with experimental studies on the performance and degradation of indium-based model catalysts for methanol synthesis. In detail, the reversibility of phase transitions in the In2 O3 /In(OH)3 system under industrial methanol synthesis conditions are investigated depending on conversion, temperature and feed ratio. The dummy catalytic cycle model predicts a peculiar degradation behavior of In(OH)3 at 275 °C depending on the water formed either by methanol synthesis or the competing reverse water-gas-shift reaction. These results were validated by dedicated experimental studies confirming the predicted trends. Moreover, X-ray diffraction and thermogravimetric analysis proved the ensuing phase transition between the indium species. Finally, the validated model is used to predict how hydrogen drop out will affect the stability of the catalyst and derive practical strategies to prevent irreversible catalyst degradation.

Carbon coated In2O3 hollow tubes embedded with ultra-low content ZnO quantum dots as catalysts for CO2 hydrogenation to methanol

CO₂ hydrogenation coupled with renewable energy to produce methanol is of great interest. Carbon coated In₂O₃ hollow tube catalysts embedded with ultra-low content ZnO quantum dots (QDs) were synthesized for CO₂ hydrogenation to methanol. ZnO-In₂O₃-II catalyst had the highest CO₂ and H₂ adsorption capacity, which demonstrated the highest methanol formation rate. When CO₂ conversion was 8.9%, methanol selectivity still exceeded 86% at 3.0 MPa and 320 °C, and STY of methanol reached 0.98 g_MeOHh^-1g_cat^-1 at 350 °C. The ZnO/In₂O₃ QDs heterojunctions were formed at the interface between ZnO and In₂O₃(222). The ZnO/In₂O₃ heterojunctions, as a key structure to promote the CO₂ hydrogenation to methanol, not only enhanced the interaction between ZnO and In₂O₃ as well as CO₂ adsorption capacity, but also accelerated the electron transfer from In³⁺ to Zn²⁺. ZnO QDs boosted the dissociation and activation of H₂. The carbon layer coated on In₂O₃ surface played a role of hydrogen spillover medium, and the dissociated H atoms were transferred to the CO₂ adsorption sites on the In₂O₃ surface through the carbon layer, promoting the reaction of H atoms with CO₂ more effectively. In addition, the conductivity of carbon enhanced the electron transfer from In³⁺ to Zn²⁺. The combination of the ZnO/In₂O₃ QDs heterojunctions and carbon layer greatly improved the methanol generation activity.

Molecular Dynamics Approach to the Physical Mixture of In2O3 and ZrO2: Defect Formation and Ionic Diffusion

Recent research on the use of physical mixtures In₂O₃-ZrO₂ has raised interesting questions as to how their combination enhances catalytic activity and selectivity. Specifically, the relationship between oxygen diffusion and defect formation and the epitaxial tension in the mixture should be further investigated. In this study, we aim to clarify some of these relationships through a molecular dynamics approach. Various potentials for the two oxides are compared and selected to describe the physical mixture of In₂O₃ and ZrO₂. Different configurations of each single crystal and their physical mixture are simulated, and oxygen defect formation and diffusion are measured and compared. Significant oxygen defect formation is found in both crystals. In₂O₃ seems to be stabilized by the mixture, while ZrO₂ is destabilized. Similar results were found for the ZrO₂ doping with In and ln₂O₃ doping with Zr. The results explain the high activity and selectivity catalyst activity of the mixture for the production of isobutylene from ethanol.

Electron Regulation of Single Indium Atoms at the Active Oxygen Vacancy of In2 O3 (110) for Production of Acetic Acid and Acetone through Direct Coupling of CH4 with CO2

The production of acetic acid and acetone from the direct coupling of CO₂ and CH₄ on the doped In₂ O₃ (110) surface has been studied by extensive first-principles calculations, and the Ga or Al substitution for the single In atom at the active oxygen vacancy of In₂ O₃ (110) can stabilize the reaction species and reduce the free energy barrier of the rate-limiting C-H activation for the conversion of CO₂ and CH₄ to acetic acid. Herein, the metal doping lowers the energy level of partially empty s and p orbitals of In₁ at the oxygen vacancy site and manipulates its electronic properties, resulting in the activity improvement. The stable intermediate with the newly-formed CH₃ COO* has the available In₁ site for subsequent CH₄ activation, which may initiate the direct C-C coupling of CH₃ COO* and CH₃ * to yield C3 species on the doped In₂ O₃ (110). These findings suggest that the metal doping of the active oxygen vacancy opens an avenue for the carbon-chain growth through heterogeneously catalytic coupling of CO₂ and CH₄ .

A Highly Active Au/In2O3-ZrO2 Catalyst for Selective Hydrogenation of CO2 to Methanol

A novel gold catalyst supported by In2O3-ZrO2 with a solid solution structure shows a methanol selectivity of 70.1% and a methanol space–time yield (STY) of 0.59 gMeOH h−1 gcat−1 for CO2 hydrogenation to methanol at 573 K and 5 MPa. The ZrO2 stabilizes the structure of In2O3, increases oxygen vacancies, and enhances CO2 adsorption, causing the improved activity.

Palladium doping of In2O3 towards a general and selective catalytic hydrogenation of amides to amines and alcohols

The first general heterogeneous hydrogenation of amides to amines and alcohols is performed under additive-free conditions and without product de-aromatization by applying a Pd-doped In₂O₃ catalyst.