Atomically dispersed Ptn+ species as highly active sites in Pt/In2O3 catalysts for methanol synthesis from CO2 hydrogenation

Scaling relations of CO2 hydrogenation and dissociation on single metal atom doped In2O3 catalysts with promoted oxygen vacancy sites

In this work, we conducted a computational study on single atom doped In2O3 catalysts with 12 transition metals (Fe-Cu, Ru-Ag, Os-Au) through density functional theory (DFT) calculations, by investigating the dissociation of H2, and the dissociation and hydrogenation of CO2. From the thermodynamic-kinetic scaling relationships such as Brønsted-Evans-Polanyi (BEP) and transition-state scaling (TSS) relations, we establish the descriptors for the energy barriers and improve our understanding of the synergistic catalytic effect of oxygen vacancies and single atoms. We find that the adsorption energy of the H adatom on the perfect surface can serve as an effective descriptor for the dissociation energy barrier of H2 on this surface, and the formation energy of the oxygen vacancy can serve as an effective descriptor for the energy barrier of CO2 hydrogenation to HCOO as well as the energy barrier of CO2 direct dissociation.

Comprehensive Insight into Indium Oxide‐Based Catalysts for CO2 Hydrogenation: Thermal, Photo, and Photothermal Catalysis

The conversion of carbon dioxide (CO2) into value‐added chemicals presents an innovative pathway for advancing the low‐carbon clean energy revolution, contributing significantly to CO2 emission reduction and resource utilization. Recently, In2O3‐based catalysts have emerged as a promising frontier in CO2 hydrogenation research. This review provides a comprehensive introduction of the latest advancements in the application of In2O3‐based catalysts across thermal, photocatalytic, and photothermal catalysis platforms. The review examines critical aspects such as structural properties, active sites, reaction mechanisms, performance enhancement, product impact, and the development of multi‐functional catalytic systems. Thermal Catalysis for CO2 hydrogenation involves the application of elevated temperatures to initiate and drive the hydrogenation reactions. Photocatalysis, on the other hand, harnesses light energy to facilitate these reactions. Among these approaches, photothermal catalysis has emerged as a particularly promising method for CO2 hydrogenation, offering several advantages over both thermal catalysis and photocatalysis. These advantages include more efficient energy utilization, a broader range of reaction conditions, enhanced synergistic effects, selective activation, and improved environmental sustainability. This review not only summarizes the current state of research in this field but also may provide critical insights and guidance for future studies aimed at advancing artificial carbon cycling processes.

Design Principles of Catalytic Materials for CO2 Hydrogenation to Methanol

Heterogeneous catalysts are essential for thermocatalytic CO2 hydrogenation to methanol, a key route for sustainable production of this vital platform chemical and energy carrier. The primary catalyst families studied include copper-based, indium oxide-based, and mixed zinc-zirconium oxides-based materials. Despite significant progress in their design, research is often compartmentalized, lacking a holistic overview needed to surpass current performance limits. This perspective introduces generalized design principles for catalytic materials in CO2-to-methanol conversion, illustrating how complex architectures with improved functionality can be assembled from simple components (e.g., active phases, supports, and promoters). After reviewing basic concepts in CO2-based methanol synthesis, engineering principles are explored, building in complexity from single to binary and ternary systems. As active nanostructures are complex and strongly depend on their reaction environment, recent progress in operando characterization techniques and machine learning approaches is examined. Finally, common design rules centered around symbiotic interfaces integrating acid-base and redox functions and their role in performance optimization are identified, pinpointing important future directions in catalyst design for CO2 hydrogenation to methanol.

Electrostatic Self-Assembly Synthesis of Pd/In2O3 Nanocatalysts with Improved Performance Toward CO2 Hydrogenation to Methanol

CO2 hydrogenation to methanol has emerged as a promising strategy for achieving carbon neutrality and mitigating global warming, in which the supported Pd/In2O3 catalysts are attracting great attention due to their high selectivity. Nonetheless, conventional impregnation methods induce strong metal-support interaction (SMSI) between Pd and In2O3, which leads to the excessive reduction of In2O3 and the formation of undesirable PdIn alloy in hydrogen-rich atmospheres. Herein, we innovatively synthesized Pd/In2O3 nanocatalysts by the electrostatic self-assembly process between surface-modified composite precursors with opposite charges. And the organic ligands concurrently serve as Pd nanoparticle protective agents. The resultant Pd/In2O3 nanocatalyst demonstrates the homogeneous distribution of Pd nanoparticles with controllable sizes on In2O3 supports and the limited formation of PdIn alloy. As a result, it exhibits superior selectivity and stability compared to the counterparts synthesized by the conventional impregnation procedure. Typically, it attains a maximum methanol space-time yield of 0.54 gMeOH h-1gcat -1 (300 °C, 3.5 MPa, 21,000 mL gcat -1 h-1). Notably, the correlation characterization results reveal the significant effect of small-size, highly dispersed Pd nanoparticles in mitigating MSI. These results provide an alternative strategy for synthesizing highly efficient Pd/In2O3 catalysts and offer a new insight into the strong metal-support interaction.

Thermochemical CO2 Reduction to Methanol over Metal-Based Single-Atom Catalysts (SACs): Outlook and Challenges for Developments

The conversion of thermodynamically inert CO2 into methanol holds immense promise for addressing the pressing environmental and energy challenges of our time. This article offers a succinct overview of the development of single-atom catalysts (SACs) for thermochemical hydrogenation of CO2 to methanol, encompassing research advancements, advantages, potential hurdles, and other essential aspects related to these catalysts. Our aim of this work is to provide a deeper understanding of the intricacies of the catalytic structures of the single-atom sites and their unique structure-activity relationships in catalyzing the conversion of CO2 to methanol. We also present insights into the optimal design of SACs, drawing from our own research and those of fellow scientists. This research thrust is poised to contribute significantly to the development of next-generation SACs, which are crucial in advancing the sustainable production of methanol from CO2.

Sustainable methanol production from carbon dioxide: advances, challenges, and future prospects

The urgent need to address global carbon emissions and promote sustainable energy solutions has led to a growing interest in carbon dioxide (CO2) conversion technologies. Among these, the transformation of CO2 into methanol (MeOH) has gained prominence as an effective mitigation strategy. This review paper provides a comprehensive exploration of recent advances and applications in the direct utilization of CO2 for the synthesis of MeOH, encompassing various aspects from catalysts to market analysis, environmental impact, and future prospects. We begin by introducing the current state of CO2 mitigation strategies, highlighting the significance of carbon recycling through MeOH production. The paper delves into the chemistry and technology behind the conversion of CO2 into MeOH, encompassing key themes such as feedstock selection, material and energy supply, and the various conversion processes, including chemical, electrochemical, photochemical, and photoelectrochemical pathways. An in-depth analysis of heterogeneous and homogeneous catalysts for MeOH synthesis is provided, shedding light on the advantages and drawbacks of each. Furthermore, we explore diverse routes for CO2 hydrogenation into MeOH, emphasizing the technological advances and production processes associated with this sustainable transformation. As MeOH holds a pivotal role in a wide range of chemical applications and emerges as a promising transportation fuel, the paper explores its various chemical uses, transportation, storage, and distribution, as well as the evolving MeOH market. The environmental and energy implications of CO2 conversion to MeOH are discussed, including a thermodynamic analysis of the process and cost and energy evaluations for large-scale catalytic hydrogenation.

Atomic and Electronic Structures of Co-Doped In2O3 from Experiment and Theory

The synthesis and properties of stoichiometric, reduced, and Co-doped In2O3 are described in the light of several experimental techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet (UV)-visible spectroscopy, porosimetry, and density functional theory (DFT) methods on appropriate models. DFT-based calculations provide an accurate prediction of the atomic and electronic structure of these systems. The computed lattice parameter is linearly correlated with the experimental result in the Co concentration ranging from 1.0 to 5.0%. For higher Co concentrations, the theoretical-experimental analysis of the results indicates that the dopant is likely to be preferentially present at surface sites. The analysis of the electronic structure supports the experimental assignment of Co2+ for the doped material. Experiments and theory find that the presence of Co has a limited effect on the material band gap.

Structured Catalysts and Catalytic Processes: Transport and Reaction Perspectives

The structure of catalysts determines the performance of catalytic processes. Intrinsically, the electronic and geometric structures influence the interaction between active species and the surface of the catalyst, which subsequently regulates the adsorption, reaction, and desorption behaviors. In recent decades, the development of catalysts with complex structures, including bulk, interfacial, encapsulated, and atomically dispersed structures, can potentially affect the electronic and geometric structures of catalysts and lead to further control of the transport and reaction of molecules. This review describes comprehensive understandings on the influence of electronic and geometric properties and complex catalyst structures on the performance of relevant heterogeneous catalytic processes, especially for the transport and reaction over structured catalysts for the conversions of light alkanes and small molecules. The recent research progress of the electronic and geometric properties over the active sites, specifically for theoretical descriptors developed in the recent decades, is discussed at the atomic level. The designs and properties of catalysts with specific structures are summarized. The transport phenomena and reactions over structured catalysts for the conversions of light alkanes and small molecules are analyzed. At the end of this review, we present our perspectives on the challenges for the further development of structured catalysts and heterogeneous catalytic processes.

Computational screening of single-atom doped In2O3 catalysts for the reverse water gas shift reaction

The reverse water gas shift (RWGS) reaction is an important method for converting carbon dioxide (CO2) into valuable chemicals and fuels by hydrogenation. In this paper, the catalytic activity of single-atom metal-doped (M = Pt, Ir, Pd, Rh, Cu, Ni) indium oxide (c-In2O3) catalysts in the cubic phase for the RWGS reaction was investigated using density functional theory (DFT) calculations. This was achieved by identifying metal sites, screening oxygen vacancies, followed by further calculating the energy barriers for the direct and indirect dissociation pathways of the RWGS reaction. Our results show that the single-atom dopant in the indium oxide lattice promotes the creation of oxygen vacancies on the In2O3 surface, thereby facilitating the adsorption and activation of CO2 by the oxide surface and initiating the subsequent RWGS reaction. Furthermore, we find that the oxygen vacancy (OV) formation energy on the surface of the single-atom metal doped c-In2O3(111) surface can be used as a descriptor for CO2 adsorption, and the higher the OV formation energy, the more stable the CO2 adsorption structure is. The Cu/In2O3 structure has relatively high energy barriers for both direct (1.92 eV) and indirect dissociation (2.09 eV) in the RWGS reaction, indicating its low RWGS reactivity. In contrast, the Ir/In2O3 and Rh/In2O3 structures are more conducive to the direct dissociation of CO2 into CO, which may serve as more efficient RWGS catalysts. Furthermore, microkinetic simulations show that single atom metal doping to In2O3 enhances CO2 conversion, especially under high reaction temperatures, where the formation of oxygen vacancies is the limiting factor for CO2 reactivity on the M/In2O3 (M = Cu, Ir, Rh) models. Among these three single-atom catalysts, the Ir/In2O3 model was predicted to have the best CO2 reactivity at reaction temperatures above 573 K.

Al Promotion of In2O3 for CO2 Hydrogenation to Methanol

In2O3 is a promising catalyst for the hydrogenation of CO2 to methanol, relevant to renewable energy storage in chemicals. Herein, we investigated the promoting role of Al on In2O3 using flame spray pyrolysis to prepare a series of In2O3-Al2O3 samples in a single step (0-20 mol % Al). Al promoted the methanol yield, with an optimum being observed at an Al content of 5 mol %. Extensive characterization showed that Al can dope into the In2O3 lattice (maximum ∼ 1.2 mol %), leading to the formation of more oxygen vacancies involved in CO2 adsorption and methanol formation. The rest of Al is present as small Al2O3 domains at the In2O3 surface, blocking the active sites for CO2 hydrogenation and contributing to higher CO selectivity. At higher Al content (≥10 mol % Al), the particle size of In2O3 decreases due to the stabilizing effect of Al2O3. Nevertheless, these smaller particles are prone to sintering during CO2 hydrogenation since they appear to be more easily reduced. These findings show subtle effects of a structural promoter such as Al on the reducibility and texture of In2O3 as a CO2 hydrogenation catalyst.

Reaction-Induced Metal-Metal Oxide Interactions in Pd-In2 O3 /ZrO2 Catalysts Drive Selective and Stable CO2 Hydrogenation to Methanol

Ternary Pd-In2 O3 /ZrO2 catalysts exhibit technological potential for CO2 -based methanol synthesis, but developing scalable systems and comprehending complex dynamic behaviors of the active phase, promoter, and carrier are key for achieving high productivity. Here, we show that the structure of Pd-In2 O3 /ZrO2 systems prepared by wet impregnation evolves under CO2 hydrogenation conditions into a selective and stable architecture, independent of the order of addition of Pd and In phases on the zirconia carrier. Detailed operando characterization and simulations reveal a rapid restructuring driven by the metal-metal oxide interaction energetics. The proximity of InPdx alloy particles decorated by InOx layers in the resulting architecture prevents performance losses associated with Pd sintering. The findings highlight the crucial role of reaction-induced restructuring in complex CO2 hydrogenation catalysts and offer insights into the optimal integration of acid-base and redox functions for practical implementation.

Fast-Response Nickel-Promoted Indium Oxide Catalysts for Carbon Dioxide Hydrogenation from Intermittent Solar Hydrogen

Construction of a "net-zero-emission" system through CO2 hydrogenation to methanol with solar energy is an eco-friendly way to mitigate the greenhouse effect. Traditional CO2 hydrogenation demands centralized mass production for cost reduction with mass water electrolysis for hydrogen supply. To achieve continuous reaction with intermittent and fluctuating flow of H2 on a small-scale for distributed application scenarios, modulating the catalyst interface environment and chemical adsorption capacity to adapt fluctuating reaction conditions is highly desired. This paper describes a distributed clean CO2 utilization system in which the surface structure of catalysts is carefully regulated. The Ni catalyst with unsaturated electrons loaded on In2 O3 can reduce the dissociation energy of H2 to overcome the slow response of intermittent H2 supply, exhibiting a faster response (12 min) than bare oxide catalysts (42 min). Moreover, the introduction of Ni enhances the sensitivity of the catalyst to hydrogen, yielding a Ni/In2 O3 catalyst with a good performance at lower H2 concentrations with a 15 times adaptability for wider hydrogen fluctuation range than In2 O3 , greatly reducing the negative impact of unstable H2 supplies derived from renewable energies.

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.

Recent Advances of Indium Oxide-Based Catalysts for CO2 Hydrogenation to Methanol: Experimental and Theoretical

Methanol synthesis from the hydrogenation of carbon dioxide (CO₂) with green H₂ has been proven as a promising method for CO₂ utilization. Among the various catalysts, indium oxide (In₂O₃)-based catalysts received tremendous research interest due to the excellent methanol selectivity with appreciable CO₂ conversion. Herein, the recent experimental and theoretical studies on In₂O₃-based catalysts for thermochemical CO₂ hydrogenation to methanol were systematically reviewed. It can be found that a variety of steps, such as the synthesis method and pretreatment conditions, were taken to promote the formation of oxygen vacancies on the In₂O₃ surface, which can inhibit side reactions to ensure the highly selective conversion of CO₂ into methanol. The catalytic mechanism involving the formate pathway or carboxyl pathway over In₂O₃ was comprehensively explored by kinetic studies, in situ and ex situ characterizations, and density functional theory calculations, mostly demonstrating that the formate pathway was extremely significant for methanol production. Additionally, based on the cognition of the In₂O₃ active site and the reaction path of CO₂ hydrogenation over In₂O₃, strategies were adopted to improve the catalytic performance, including (i) metal doping to enhance the adsorption and dissociation of hydrogen, improve the ability of hydrogen spillover, and form a special metal-In₂O₃ interface, and (ii) hybrid with other metal oxides to improve the dispersion of In₂O₃, enhance CO₂ adsorption capacity, and stabilize the key intermediates. Lastly, some suggestions in future research were proposed to enhance the catalytic activity of In₂O₃-based catalysts for methanol production. The present review is helpful for researchers to have an explicit version of the research status of In₂O₃-based catalysts for CO₂ hydrogenation to methanol and the design direction of next-generation catalysts.

Challenges and Opportunities in Engineering the Electronic Structure of Single-Atom Catalysts

Controlling the electronic structure of transition-metal single-atom heterogeneous catalysts (SACs) is crucial to unlocking their full potential. The ability to do this with increasing precision offers a rational strategy to optimize processes associated with the adsorption and activation of reactive intermediates, charge transfer dynamics, and light absorption. While several methods have been proposed to alter the electronic characteristics of SACs, such as the oxidation state, band structure, orbital occupancy, and associated spin, the lack of a systematic approach to their application makes it difficult to control their effects. In this Perspective, we examine how the electronic configuration of SACs can be engineered for thermochemical, electrochemical, and photochemical applications, exploring the relationship with their activity, selectivity, and stability. We discuss synthetic and analytical challenges in controlling and discriminating the electronic structure of SACs and possible directions toward closing the gap between computational and experimental efforts. By bringing this topic to the center, we hope to stimulate research to understand, control, and exploit electronic effects in SACs and ultimately spur technological developments.

The Promoting Role of Ni on In2O3 for CO2 Hydrogenation to Methanol

Ni-promoted indium oxide (In2O3) is a promising catalyst for the selective hydrogenation of CO2 to CH3OH, but the nature of the active Ni sites remains unknown. By employing density functional theory and microkinetic modeling, we elucidate the promoting role of Ni in In2O3-catalyzed CO2 hydrogenation. Three representative models have been investigated: (i) a single Ni atom doped in the In2O3(111) surface, (ii) a Ni atom adsorbed on In2O3(111), and (iii) a small cluster of eight Ni atoms adsorbed on In2O3(111). Genetic algorithms (GAs) are used to identify the optimum structure of the Ni8 clusters on the In2O3 surface. Compared to the pristine In2O3(111) surface, the Ni8-cluster model offers a lower overall barrier to oxygen vacancy formation, whereas, on both single-atom models, higher overall barriers are found. Microkinetic simulations reveal that only the supported Ni8 cluster can lead to high methanol selectivity, whereas single Ni atoms either doped in or adsorbed on the In2O3 surface mainly catalyze CO formation. Hydride species obtained by facile H2 dissociation on the Ni8 cluster are involved in the hydrogenation of adsorbed CO2 to formate intermediates and methanol. At higher temperatures, the decreasing hydride coverage shifts the selectivity to CO. On the Ni8-cluster model, the formation of methane is inhibited by high barriers associated with either direct or H-assisted CO activation. A comparison with a smaller Ni6 cluster also obtained with GAs exhibits similar barriers for key rate-limiting steps for the formation of CO, CH4, and CH3OH. Further microkinetic simulations show that this model also has appreciable selectivity to methanol at low temperatures. The formation of CO over single Ni atoms either doped in or adsorbed on the In2O3 surface takes place via a redox pathway involving the formation of oxygen vacancies and direct CO2 dissociation.

First-principles study of CO2 hydrogenation to formic acid on single-atom catalysts supported on SiO2

The hydrogenation of CO₂ into valuable chemical fuels reduces the atmospheric CO₂ content and also has broad economic prospects. Support is essential for catalysts, but many of the reported support materials cannot meet the requirements of accessibility and durability. Herein, we theoretically designed a series of single-atom noble metals anchored on a SiO₂ surface for CO₂ hydrogenation using density functional theory (DFT) calculations. Through theoretical evaluation of the formation energy, hydrogen dissociation capacity, and activity of CO₂ hydrogenation, we found that Ru@SiO₂ is a promising candidate for CO₂ hydrogenation to formic acid. The energy barrier of the rate-determining step of the entire conversion process is 23.9 kcal mol^-1; thus, the reaction can occur under mild conditions. In addition, active and stable origins were revealed through electronic structure analysis. The charge of the metal atom is a good descriptor of the catalytic activity. The Pearson correlation coefficient (PCC) between metal charge and its CO₂ hydrogenation barrier is 0.99. Two solvent models were also used to investigate hydrogen spillover processes and the reaction path was searched by the climbing image nudged-elastic-band (CI-NEB) method. The results indicated that the explicit solvent model could not be simplified into a few solvent molecules, leading to a large difference in the reaction paths. This work will serve as a reference for the future design of more efficient catalysts for CO₂ hydrogenation.

Role of Zr loading into In2O3 catalysts for the direct conversion of CO2/CO mixtures into light olefins

The effect of the ZrO₂ content on the performance (activity, selectivity, stability) of In₂O₃-ZrO₂ catalyst has been studied on the hydrogenation of CO₂/CO mixtures. This effect is a key feature for the viability of using In₂O₃-ZrO₂/SAPO-34 tandem catalysts for the direct conversion of CO₂ and syngas into olefins via oxygenates as intermediates. The interest of co-feeding syngas together with CO₂ resides in jointly valorizing syngas derived from biomass or wastes (via gasification) and supplying the required H₂. The experiments of methanol synthesis and direct synthesis of olefins, with In₂O₃-ZrO₂ and In₂O₃-ZrO₂/SAPO-34 catalysts, respectively, have been carried out under the appropriate conditions for the direct olefins synthesis (400 °C, 30 bar, H₂/CO_X ratio = 3) in an isothermal fixed bed reactor at low space time values (kinetic conditions) to evaluate the behavior and deactivation of the catalysts. The Zr/In ratio of 1/2 favors the conversion of CO₂ and CO_X, attaining good oxygenates selectivity, and prevents the sintering attributable to the over-reduction of the In₂O₃ (more significant for syngas feeds). The improvement is more remarkable in the direct olefins synthesis, where the thermodynamic equilibrium of methanol formation is displaced, and methanation suppressed (in a greater extent for feeds with high CO content). With the In₂O₃-ZrO₂/SAPO-34 tandem catalysts, the conversion of CO_x almost 5 folds respect oxygenates synthesis with In₂O₃-ZrO₂ catalyst, meaning the yield of the target products boosts from ∼0.5% of oxygenates to >3% of olefins (selectivity >70%) for mixtures of CO₂/CO_X of 0.5, where an optimum performance has been obtained.

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.

A minireview on the synthesis of single atom catalysts

Single atom catalysis is a prosperous and rapidly growing research field, owing to the remarkable advantages of single atom catalysts (SACs), such as maximized atom utilization efficiency, tailorable catalytic activities as well as supremely high catalytic selectivity. Synthesis approaches play crucial roles in determining the properties and performance of SACs. Over the past few years, versatile methods have been adopted to synthesize SACs. Herein, we give a thorough and up-to-date review on the progress of approaches for the synthesis of SACs, outline the general principles and list the advantages and disadvantages of each synthesis approach, with the aim to give the readers a clear picture and inspire more studies to exploit novel approaches to synthesize SACs effectively.

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.

In–Co–Zn/C–N catalysts derived from ZIFs for selective hydrogenation of CO2 into methanol

In2O3 combines ZIF derived Co–Zn/C–N catalyst perform a CO2 conversion of 7.0% with methanol selectivity over 77% and the STY of methanol is 3.3 mmol gcat−1 h−1 under the condition of CO2/H2 = 3 : 1, 2 MPa, 300 °C and GHSV = 6 L gcat−1 h−1.

Modulating optical properties and interfacial electron transfer of CsPbBr3 perovskite nanocrystals via indium ion and chlorine ion co-doping

In this work, we demonstrated an in situ approach for doping CsPbBr₃ nanocrystals (NCs) with In³⁺ and Cl^- with a ligand-assisted precipitation method at room temperature. The In³⁺ and Cl^- co-doped NCs are characterized by the powder x-ray diffraction patterns, ultraviolet-visible, photoluminescence (PL) spectroscopy, time-resolved PL (TRPL), ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy. Based on PL and TRPL results, the non-radiative nature of In³⁺-doping induced localized impurity states is revealed. Furthermore, the impact of In³⁺ and Cl^- doping on charge transfer (CT) from the NCs to molecular acceptors was investigated and the results indicate that the CT at the interface of NCs can be tuned and promoted by In³⁺ and Cl^- co-doping. This enhanced CT is attributed to the enlarged energy difference between relevant states of the molecular acceptor and the NCs by In³⁺ and Cl^- upon co-doping. This work provides insight into how to control interfacial CT in perovskite NCs, which is important for optoelectronic applications.

Ni-In Synergy in CO2 Hydrogenation to Methanol

Indium oxide (In2O3) is a promising catalyst for selective CH3OH synthesis from CO2 but displays insufficient activity at low reaction temperatures. By screening a range of promoters (Co, Ni, Cu, and Pd) in combination with In2O3 using flame spray pyrolysis (FSP) synthesis, Ni is identified as the most suitable first-row transition-metal promoter with similar performance as Pd-In2O3. NiO-In2O3 was optimized by varying the Ni/In ratio using FSP. The resulting catalysts including In2O3 and NiO end members have similar high specific surface areas and morphology. The main products of CO2 hydrogenation are CH3OH and CO with CH4 being only observed at high NiO loading (≥75 wt %). The highest CH3OH rate (∼0.25 gMeOH/(gcat h), 250 °C, and 30 bar) is obtained for a NiO loading of 6 wt %. Characterization of the as-prepared catalysts reveals a strong interaction between Ni cations and In2O3 at low NiO loading (≤6 wt %). H2-TPR points to a higher surface density of oxygen vacancy (Ov) due to Ni substitution. X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and electron paramagnetic resonance analysis of the used catalysts suggest that Ni cations can be reduced to Ni as single atoms and very small clusters during CO2 hydrogenation. Supportive density functional theory calculations indicate that Ni promotion of CH3OH synthesis from CO2 is mainly due to low-barrier H2 dissociation on the reduced Ni surface species, facilitating hydrogenation of adsorbed CO2 on Ov.

Atomically dispersed Pd-Ru dual sites in an amorphous matrix towards efficient phenylacetylene semi-hydrogenation

Optimizing the active sites to balance the conversion and selectivity of the target reaction has long been a challenging quest in developing noble metal-based catalysts. By dispersing Pd and Ru in an amorphous zirconium hydrogen phosphate matrix cross-linked by ionic inorganic oligomers, highly diluted noble metal (<0.2 mol%) can be utilized as dual single-atom sites in oxides for the semi-hydrogenation of phenylacetylene with optimized conversion and selectivity (both >90%) to styrene. In situ DRIFT-IR results suggested the fast generation of surface hydroxyl groups during the catalytic reaction, indicating the high efficiency of the single-atom sites to dissociate bound H2. This work provides an easily scaled-up method for the production of cost-effective single-atom catalysts extendable to various oxide matrices.

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.

Nanostructure of nickel-promoted indium oxide catalysts drives selectivity in CO2 hydrogenation

Metal promotion in heterogeneous catalysis requires nanoscale-precision architectures to attain maximized and durable benefits. Herein, we unravel the complex interplay between nanostructure and product selectivity of nickel-promoted In2O3 in CO2 hydrogenation to methanol through in-depth characterization, theoretical simulations, and kinetic analyses. Up to 10 wt.% nickel, InNi3 patches are formed on the oxide surface, which cannot activate CO2 but boost methanol production supplying neutral hydrogen species. Since protons and hydrides generated on In2O3 drive methanol synthesis rather than the reverse water-gas shift but radicals foster both reactions, nickel-lean catalysts featuring nanometric alloy layers provide a favorable balance between charged and neutral hydrogen species. For nickel contents >10 wt.%, extended InNi3 structures favor CO production and metallic nickel additionally present produces some methane. This study marks a step ahead towards green methanol synthesis and uncovers chemistry aspects of nickel that shall spark inspiration for other catalytic applications.

A DFT-based microkinetic study on methanol synthesis from CO2 hydrogenation over the In2O3 catalyst

In this work, we performed density functional theory (DFT)-based microkinetic simulations to elucidate the reaction mechanism of methanol synthesis on two of the most stable facets of the cubic In2O3 (c-In2O3) catalyst, namely the (111) and (110) surfaces. Our DFT calculations show that for both surfaces, it is difficult for the H atom adsorbed at the remaining surface O atom around the O vacancy (Ov) active site to migrate to an O adsorbed at the Ov due to the very high energy barrier involved. In addition, we also find that the C-O bond in the bt-CO2* chemisorption structure can directly break to form CO with a lower energy barrier than that in its hydrogenation to the COOH* intermediate in the COOH route. However, our microkinetic simulations suggest that for both surfaces, CO2 deoxygenation to form CO in both pathways, namely the COOH and CO-O routes, are kinetically slower than methanol formation under typical steady state conditions assuming a CO2 conversion of 10% and a CO selectivity of 1%. Although these results agree with previous experimental observations at relatively low reaction temperature, where methanol formation dominates, they cannot explain the predominant formation of CO at relatively high reaction temperature. We tentatively attribute this to the simplicity of our microkinetic model as well as possible structural changes of the catalyst at relatively high reaction temperature. Furthermore, although the rate-determining step (RDS) from the degree of rate control (DRC) analysis is usually consistent with that judged from the DFT calculated energy barriers, for CO2 hydrogenation to methanol over the (111) surface, our DRC analysis suggests homolytic H2 dissociation to be the rate-controlling step, which is not apparent from the DFT-calculated energy barriers. This indicates that CO2 conversion and methanol selectivity over the (111) surface can be further enhanced if homolytic H2 dissociation can be accelerated for instance by introducing transition metal dopants as already shown by some experimental observations.