Density functional theoretical study of Au4/In2O3 catalyst for CO2 hydrogenation to methanol: The strong metal-support interaction and its effect

H-assisted CO2 dissociation on PdnPt(4-n)/In2O3 catalysts: a density functional theory study

CO2 hydrogenation into valuable chemical compounds can effectively address the issues of greenhouse gas emissions and energy scarcity. The activation and dissociation processes of CO2 are crucial for its reduction reactions, but the effects of *H adatoms on the C-O cleavage are still confusing. This study investigates the H-assisted CO2 dissociation pathways on the PdnPt(4-n)/In2O3 (n = 0-4) catalysts via DFT calculation. Initially, the adsorption properties of *H2, *COOH, and *HCOO species are calculated. Then, two H-assisted CO2 dissociation channels, i.e., *CO2 + *H → *COOH → *CO + *OH and *CO2 + *H → *HCOO → *CHO + *O, are studied. Results show that Pt and Pd promote the CO2 hydrogenation and C-O bond cleavage reactions, respectively. In comparison to CO2 direct dissociation, the COOH-mediated and HCOO-mediated channels facilitate and impede the C-O bond cleavage, respectively. Overall, the Pd3Pt/In2O3 constituent is suggested for the H-assisted CO2 dissociation reaction. The electronic effects of the PdnPt(4-n) bimetals adjust the stabilities of the intermediates and barriers of the elementary steps, and the interactions between PdnPt(4-n) and In2O3 provide extra sites for the adsorbates and reaction steps. This study reveals the effects of *H on the C-O bond dissociation processes and provides useful insight into designing PdPt/In2O3 catalysts for CO2 hydrogenation reactions.

Dual-Photosensitizer Synergy Empowers Ambient Light Photoactivation of Indium Oxide for High-Performance NO2 Sensing

Light-activated chemiresistors offer a powerful approach to achieving lower-temperature gas sensing with unprecedented sensitivities. However, an incomplete understanding of how photoexcited charge carriers enhance sensitivity obstructs the rational design of high-performance sensors, impeding the practical utilization under commonly accessible light sources instead of ultraviolet or higher-energy sources. Here, a rational approach is presented to modulate the electronic properties of the parent metal oxide phase, exemplified by this model system of Bi-doped In2O3 nanofibers decorated with Au nanoparticles (NPs) that exhibit superior NO2 sensing performance. Bi doping introduces mid-gap energy levels into In2O3, promoting photoactivation even under visible blue light. Additionally, green-absorbing plasmonic Au NPs facilitate electron transfer across the heterojunction, extending the photoactive region toward the green light. It is revealed that the direct involvement of photogenerated charge carriers in gas adsorption and desorption processes is pivotal for enhancing gas sensing performance. Owing to the synergistic interplay between the Bi dopants and the Au NPs, the Au-BixIn2-xO3 (x = 0.04) sensing layers attain impressive response values (Rg/Ra = 104 at 0.6 ppm NO2) under green light illumination and demonstrate practical viability through evaluation under simulated mixed-light conditions, all of which significantly outperforms previously reported visible light-activated NO2 sensors.

Boosting oxygen vacancies by modulating the morphology of Au decorated In2O3 with enhanced CO2 hydrogenation activity to CH3OH

CO2 hydrogenation to methanol has become one of the most promising ways for CO2 utilization, however, the CO2 conversion rate and methanol selectivity of this reaction still need to be improved for industrial application. Here we investigated the structure-activity relationship for CO2 conversion to methanol of In2O3-based catalysts by modulating morphology and decorating Au. Three different Au/In2O3 catalysts were prepared, their activity follow the sequence of Au/In2O3-nanosphere (Au/In2O3-NS) > Au/In2O3-nanoplate (Au/In2O3-NP) > Au/In2O3-hollow microsphere (Au/In2O3-HM). Au/In2O3-NS exhibited the best performance with good CO2 conversion of 12.7%, high methanol selectivity of 59.8%, and large space time yield of 0.32 gCH3OH/(hr·gcat) at 300°C. The high performance of Au/In2O3-NS was considered as the presence of Au. It contributes to the creation of more surface oxygen vacancies, which further promoted the CO2 adsorption and facilitated CO2 activation to form the formate intermediates towards methanol. This work clearly suggests that the activity of In2O3 catalyst can be effective enhanced by structure engineering and Au decorating.

Importance of Metal-Support Interactions for CO2 Hydrogenation: An Operando Near-Ambient Pressure X-ray Photoelectron Spectroscopy Study on Gold-Loaded In2O3 and CeO2 Catalysts

Metal-support interactions, which are essential for the design of supported metal catalysts, used, e.g., for CO2 activation, are still only partially understood. In this study of gold-loaded In2O3 and CeO2 catalysts during CO2 hydrogenation using near-ambient pressure X-ray photoelectron spectroscopy, supported by near edge X-ray absorption fine structure, we demonstrate that the role of the noble metal strongly depends upon the choice of the support material. Temperature-dependent analyses of X-ray photoelectron spectra under reaction conditions reveal that gold is reduced on CeO2, enabling direct H2 activation, but oxidized on In2O3, leading to decreased activity of Au/In2O3 compared to bare In2O3. At elevated temperatures, the catalytic activity of the In2O3 catalysts strongly increases as a result of facilitated CO2 and (In2O3-based) H2 activation, while the catalytic activity of Au/CeO2 is limited by reoxidation by CO2. Our results underline the importance of operando studies for understanding metal-support interactions to enable a rational support selection in the future.

A new adsorption energy-barrier relation and its application to CO2 hydrogenation to methanol over In2O3-supported metal catalysts

Herein, we report a new adsorption energy-barrier relation, the adsorbate-dependent barrier scaling (ADBS) relation, with which the catalytic activity of In₂O₃-supported metal catalysts for CO₂ hydrogenation to methanol is predicted. It is shown that Cu, Ga, NiPt and NiPd alloys exhibit high catalytic activity for CO₂ hydrogenation to methanol.

Elucidating CO2 Hydrogenation over In2 O3 Nanoparticles using Operando UV/Vis and Impedance Spectroscopies

In₂ O₃ has emerged as a promising catalyst for CO₂ activation, but a fundamental understanding of its mode of operation in CO₂ hydrogenation is still missing, as the application of operando vibrational spectroscopy is challenging due to absorption effects. In this mechanistic study, we systematically address the redox processes related to the reverse water-gas shift reaction (rWGSR) over In₂ O₃ nanoparticles, both at the surface and in the bulk. Based on temperature-dependent operando UV/Vis spectra and a novel operando impedance approach for thermal powder catalysts, we propose oxidation by CO₂ as the rate-determining step for the rWGSR. The results are consistent with redox processes, whereby hydrogen-containing surface species are shown to exhibit a promoting effect. Our findings demonstrate that oxygen/hydrogen dynamics, in addition to surface processes, are important for the activity, which is expected to be of relevance not only for In₂ O₃ but also for other reducible oxide catalysts.

Unraveling the Catalytic Performance of the Nonprecious Metal Single-Atom-Embedded Graphitic s-Triazine-Based C3N4 for CO2 Hydrogenation

Graphitic carbon nitride (g-C₃N₄) is regarded as a promising potent photoelectrocatalyst for CO₂ reduction. Here, extensive first-principles calculations and ab initio molecular dynamics (AIMD) simulations are performed to systematically explore the structural and electronic properties of nonprecious metal single-atom-embedded graphitic s-triazine-based C₃N₄ (M@gt-C₃N₄, M = Mn, Fe, Co, Ni, Cu, and Mo) monolayer materials and their catalytic performances as the single-atom catalysts (SACs) for CO₂ hydrogenation to HCOOH, CO, and CH₃OH. It is found that the atomically dispersed non-noble metal Mn, Fe, Co, and Mo sites anchored on gt-C₃N₄ can efficiently activate both H₂ and CO₂, and their coadsorbed state serves as a precursor to the hydrogenation of CO₂ to different C1 products. Among these SACs (M@gt-C₃N₄, M = Mn, Fe, Co, and Mo), Co@gt-C₃N₄ was predicted to have the best catalytic performance for CO₂ hydrogenation to C1 products, although their mechanistic details are somewhat different. The predicted energy barriers of the rate-determining steps for the conversion of CO₂ into HCOOH, CO, and CH₃OH on Co@gt-C₃N₄ are 0.58, 0.67, and 1.19 eV, respectively. The desorption of products is generally energy-demanding, but it can be facilitated remarkably by the subsequent adsorption of H₂, which regenerates M@gt-C₃N₄ for the next catalytic cycle. The present study demonstrates that the catalytic performance of gt-C₃N₄ can be well regulated by embedding the non-noble metal single atom, and the porous gt-C₃N₄ is nicely suited for the construction of high-performance single-atom catalysts.

Catalytic Hydrogenation of CO2 to Methanol: A Review

High-efficiency utilization of CO2 facilitates the reduction of CO2 concentration in the global atmosphere and hence the alleviation of the greenhouse effect. The catalytic hydrogenation of CO2 to produce value-added chemicals exhibits attractive prospects by potentially building energy recycling loops. Particularly, methanol is one of the practically important objective products, and the catalytic hydrogenation of CO2 to synthesize methanol has been extensively studied. In this review, we focus on some basic concepts on CO2 activation, the recent research advances in the catalytic hydrogenation of CO2 to methanol, the development of high-performance catalysts, and microscopic insight into the reaction mechanisms. Finally, some thinking on the present research and possible future trend is presented.

Hydrogenation of carbon dioxide (CO2) to fuels in microreactors: a review of set-ups and value-added chemicals production

A review of CO2 hydrogenation to fuels and value-added chemicals in microreactors.

Density functional theoretical study of the tungsten-doped In2O3 catalyst for CO2 hydrogenation to methanol

W doping makes CO2 hydrogenation to methanol on In2O3 kinetically more favorable based on DFT calculations.

CO2 activation and dissociation on In2O3(110) supported PdnPt(4-n) (n = 0-4) catalysts: a density functional theory study

Converting CO2 into valuable chemicals via catalytic reactions can mitigate both the greenhouse effect and energy shortage problems, thus designing efficient catalysts have attracted considerable attention over the past decades. In this work, a density functional theory (DFT) calculation was carried out to investigate the CO2 activation and dissociation processes on various PdnPt(4-n)/In2O3 (n = 0-4) catalysts. The PdnPt(4-n)/In2O3 models were initially built, and the interface sites of PdnPt(4-n)/In2O3 for CO2 adsorption were confirmed among cluster sites and substrate sites. The CO2 adsorption geometries, charger transfer, and projected density of states (PDOS) were analyzed to study the CO2-PdnPt(4-n)/In2O3 interactions. From the adsorbed *CO2, the transition states (TSs) for CO2 dissociation to form *CO and *O were gained to reveal the characteristics of the activated CO2δ-. Overall, according to the adsorption energy Eads results, the bimetallic PdPt3/In2O3 and Pd3Pt/In2O3 catalysts showed the strongest and weakest CO2 adsorption stabilities, respectively, while the Pd element addition decreases the barriers for CO2 dissociation with the priority order of Pd4 > Pd3Pt > Pd2Pt2 > PdPt3 > Pt4. The Brønsted-Evans-Polanyi (BEP) relation between activation barriers (Eb) and reaction energies E was obtained for the CO2 dissociation mechanism on PdnPt(4-n)/In2O3 catalysts with the equation of E = 0.20Eb + 0.40. Finally, the optimal Pd2Pt2/In2O3 catalyst for CO2 activation and dissociation was proposed. This study provides useful information for CO2 activation and conversation procedures on bimetal-oxide catalysts, and helps to take the optimal design of PdPt/In2O3 catalysts for the CO2 reaction.

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.