New black indium oxide—tandem photothermal CO2-H2 methanol selective catalyst

Solar Energy-Driven Reverse Water Gas Shift Reaction: Photothermal Effect, Photoelectric Activation and Selectivity Regulation

Excessive carbon dioxide (CO2) emissions are one of the main causes of the greenhouse effect. Thermal catalytic reverse water gas shift (RWGS) reaction, which is a pre reaction for Fischer-Tropsch synthesis, is considered an effective way to convert CO2 and synthesize high value-added chemicals in industry. However, traditional thermal catalysis requires a large amount of fossil fuels to drive reactions, which cannot achieve the true goal of carbon neutrality. Photothermal catalysis, as a novel conversion pathway, can achieve efficient CO2 conversion while significantly improving solar energy utilization. This review provides a detailed introduction of CO2 and H2 adsorption/activation and reaction pathways in thermal catalysis, as well as the catalytic mechanisms of thermal and chemical effects in photothermal catalytic RWGS to supply readers valuable insights on the mechanism of photothermal catalytic RWGS reaction and provide a reference for better catalyst design.

A feasible interlayer strategy for simultaneous light and heat management in photothermal catalysis

Photothermal conversion represents one crucial approach for solar energy harvesting and its exploitation as a sustainable alternative to fossil fuels; however, an efficient, cost-effective, and generalized approach to enhance the photothermal conversion processes is still missing. Herein, we develop a feasible and efficient photothermal conversion strategy that achieves simultaneous light and heat management using supported metal clusters and WSe2 interlayer toward enhanced CO2 hydrogenation photothermal catalysis. The interlayer can simultaneously reduce heat loss in the catalytic layer and improve light absorption, leading to an 8-fold higher CO2 conversion rate than the controls. The optical and thermal performance of WSe2 interlayered catalysts on different substrates was quantified using Raman spectroscopy. This work demonstrates a feasible and generalized approach for effective light and heat management in solar harvesting. It also provides important design guidelines for efficient photothermal converters that facilitate the remediation of the energy and environmental crises faced by humans.

Unraveling the molecular and growth mechanism of colloidal black In2O3-x

Black metal oxides with varying concentrations of O-vacancies display enhanced optical and catalytic properties. However, direct solution syntheses of this class of materials have been limited despite being highly advantageous given the different synthetic handles that can be leveraged towards control of the targeted material. Herein, we present an alternate colloidal synthesis of black In2O3-x nanoparticles from the simple reaction between In(acac)3 and oleyl alcohol. Growth studies by PXRD, TEM, and STEM-EDS coupled to mechanistic insights from 1H, 13C NMR revealed the particles form via two paths, one of which involves In0. We also show that variations in the synthesis atmosphere, ligand environment, and indium precursor can inhibit formation of the black In2O3-x. The optical spectrum for the black nanoparticles displayed a significant redshift when compared to pristine In2O3, consistent with the presence of O-vacancies. Raman spectra and surface analysis also supported the presence of surface oxygen vacancies in the as-synthesized black In2O3-x.

Photothermal CO2 Catalysis toward the Synthesis of Solar Fuel: From Material and Reactor Engineering to Techno-Economic Analysis

Carbon dioxide (CO2), a member of greenhouse gases, contributes significantly to maintaining a tolerable environment for all living species. However, with the development of modern society and the utilization of fossil fuels, the concentration of atmospheric CO2 has increased to 400 ppm, resulting in a serious greenhouse effect. Thus, converting CO2 into valuable chemicals is highly desired, especially with renewable solar energy, which shows great potential with the manner of photothermal catalysis. In this review, recent advancements in photothermal CO2 conversion are discussed, including the design of catalysts, analysis of mechanisms, engineering of reactors, and the corresponding techno-economic analysis. A guideline for future investigation and the anthropogenic carbon cycle are provided.

Thermocatalytic Hydrogen Production from Water at Boiling Condition

Thermochemical water-splitting cycles are technically feasible for hydrogen production from water. However, the ultrahigh operation temperature and low efficiency seriously restrict their practical application. Herein, one-step and one-pot thermocatalytic water-splitting process is reported at water boiling condition catalyzed by single atomic Pt on defective In2O3. Water splitting into hydrogen is verified by D2O isotopic experiment, with an optimized hydrogen production rate of 36.4 mmol·h-1·g-1 as calculated on Pt active sites. It is revealed that three-centered Pt1In2 surrounding oxygen vacancy as catalytic ensembles promote the dissociation of the adsorbed water into H, which transfers to singlet atomic Pt sites for H2 production. Remaining OH groups on adjacent In sites from Pt1In2 ensembles undergoes O─O bonding, hyperoxide formation and diminishing via triethylamine oxidation, water re-adsorption for completing the catalytic cycle. Current work represents an isothermal and continuous thermocatalytic water splitting under mild condition, which can re-awaken the research interest to produce H2 from water using low-grade heat and competes with photocatalytic, electrolytic, and photoelectric reactions.

Biomimetic Frustrated Lewis Pair Catalysts for Hydrogenation of CO to Methanol at Low Temperatures

The industrial production of methanol through CO hydrogenation using the Cu/ZnO/Al2O3 catalyst requires harsh conditions, and the development of new catalysts with low operating temperatures is highly desirable. In this study, organic biomimetic FLP catalysts with good tolerance to CO poison are theoretically designed. The base-free catalytic reaction contains the 1,1-addition of CO into a formic acid intermediate and the hydrogenation of the formic acid intermediate into methanol. Low-energy spans (25.6, 22.1, and 20.6 kcal/mol) are achieved, indicating that CO can be hydrogenated into methanol at low temperatures. The new extended aromatization-dearomatization effect involving multiple rings is proposed to effectively facilitate the rate-determining CO 1,1-addition step, and a new CO activation model is proposed for organic catalysts.

Wettability Engineering of Solar Methanol Synthesis

Engineering the wettability of surfaces with hydrophobic organics has myriad applications in heterogeneous catalysis and the large-scale chemical industry; however, the mechanisms behind may surpass the proverbial hydrophobic kinetic benefits. Herein, the well-studied In2O3 methanol synthesis photocatalyst has been used as an archetype platform for a hydrophobic treatment to enhance its performance. With this strategy, the modified samples facilitated the tuning of a wide range of methanol production rates and selectivity, which were optimized at 1436 μmol gcat-1 h-1 and 61%, respectively. Based on in situ DRIFTS and temperature-programmed desorption-mass spectrometry, the surface-decorated alkylsilane coating on In2O3 not only kinetically enhanced the methanol synthesis by repelling the produced polar molecules but also donated surface active H to facilitate the subsequent hydrogenation reaction. Such a wettability design strategy seems to have universal applicability, judged by its success with other CO2 hydrogenation catalysts, including Fe2O3, CeO2, ZrO2, and Co3O4. Based on the discovered kinetic and mechanistic benefits, the enhanced hydrogenation ability enabled by hydrophobic alkyl groups unleashes the potential of the surface organic chemistry modification strategy for other important catalytic hydrogenation reactions.

Enhancement of Pt-O Synergistic Sites through Titanium Vacancies for Low-Temperature Nitrogen Oxide Reduction

Improving the reaction rate of each step is significant for accelerating the multistep reaction of NO reduction by H2. However, simultaneously enhancing the activation of different gaseous reactants using single-atom catalysts remains a challenge to maximize the activity. Herein, we propose a strategy that utilizes titanium-vacancy-regulated electronic properties of single atoms and defective support (Pt1/d-TiO2) to facilitate electron transfer from edge-share O atoms (OTi) to adjacent Pt single atoms. This leads to the formation of low-valence Pt and unsaturated-charge OTi sites, which causes the catalytic reaction to follow a synergistic mechanism. Specifically, experimental and theoretical analyses demonstrate that low-valence Pt sites finely tune the adsorption of H2 molecules, consequently lowering the dissociation energy from 0.15 to as low as 0.01 eV. Moreover, using quasi-in situ spectroscopy, we clearly observe NO molecules being adsorbed on interfacial oxygen sites of a defective support. Then, the bond energy of the N-O bond is weakened through an electron acceptance-donation mechanism between unsaturated-charge OTi sites and NO, thereby facilitating NO activation. The designed single-atom catalysts with synergistic sites exhibit unmatched activity at low temperatures (above 90% NOx conversion at 100 °C), along with higher turnover frequency value (0.74 s-1) and superior stability, making them potentially suitable for industrial applications.

Photothermal Catalytic CO2 Conversion: Beyond Catalysis and Photocatalysis

In recent years, the combination of both thermal and photochemical contributions has provided interesting opportunities for solar upgrading of catalytic processes. Photothermal catalysis works at the interface between purely photochemical processes, which involve the direct conversion of photon energy into chemical energy, and classical thermal catalysis, in which the catalyst is activated by temperature. Thus, photothermal catalysis acts in two different ways on the energy path of the reaction. This combined catalysis, of which the fundamental principles will be reviewed here, is particularly promising for the activation of small reactive molecules at moderate temperatures compared to thermal catalysis and with higher reaction rates than those attained in photocatalysis, and it has gained a great deal of attention in the last years. Among the different applications of photothermal catalysis, CO₂ conversion is probably the most studied, although reaction mechanisms and photonic-thermal synergy pathways are still quite unclear and, from the reaction route point of view, it can be said that photothermal-catalytic CO₂ reduction processes are still in their infancy. This article intends to provide an overview of the principles underpinning photothermal catalysis and its application to the conversion of CO₂ into useful molecules, with application essentially as fuels but also as chemical building blocks. The most relevant specific cases published to date will be also reviewed from the viewpoint of selectivity towards the most frequent target products.

Nickel-Laden Dendritic Plasmonic Colloidosomes of Black Gold: Forced Plasmon Mediated Photocatalytic CO2 Hydrogenation

In this work, we have designed and synthesized nickel-laden dendritic plasmonic colloidosomes of Au (black gold-Ni). The photocatalytic CO₂ hydrogenation activities of black gold-Ni increased dramatically to the extent that measurable photoactivity was only observed with the black gold-Ni catalyst, with a very high photocatalytic CO production rate (2464 ± 40 mmol g_Ni^-1 h^-1) and 95% selectivity. Notably, the reaction was carried out in a flow reactor at low temperature and atmospheric pressure without external heating. The catalyst was stable for at least 100 h. Ultrafast transient absorption spectroscopy studies indicated indirect hot-electron transfer from the black gold to Ni in less than 100 fs, corroborated by a reduction in Au-plasmon electron-phonon lifetime and a bleach signal associated with Ni d-band filling. Photocatalytic reaction rates on excited black gold-Ni showed a superlinear power law dependence on the light intensity, with a power law exponent of 5.6, while photocatalytic quantum efficiencies increased with an increase in light intensity and reaction temperature, which indicated the hot-electron-mediated mechanism. The kinetic isotope effect (KIE) in light (1.91) was higher than that in the dark (∼1), which further indicated the electron-driven plasmonic CO₂ hydrogenation. Black gold-Ni catalyzed CO₂ hydrogenation in the presence of an electron-accepting molecule, methyl-p-benzoquinone, reduced the CO production rate, asserting the hot-electron-mediated mechanism. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that CO₂ hydrogenation took place by a direct dissociation path via linearly bonded Ni-CO intermediates. The outstanding catalytic performance of black gold-Ni may provide a way to develop plasmonic catalysts for CO₂ reduction and other catalytic processes using black gold.

One-Step Phase Separation for Core-Shell Carbon@Indium Oxide@Bismuth Microspheres with Enhanced Activity for CO2 Electroreduction to Formate

It is a substantial challenge to construct electrocatalysts with high activity, good selectivity, and long-term stability for electrocatalytic reduction of carbon dioxide to formic acid. Herein, bismuth and indium species are innovatively integrated into a uniform heterogeneous spherical structure by a neoteric quasi-microemulsion method, and a novel C@In₂ O₃ @Bi₅₀ core-shell structure is constructed through a subsequent one-step phase separation strategy due to melting point difference and Kirkendall effect with the nano-limiting effect of the carbon structure. This core-shell C@In₂ O₃ @Bi₅₀ catalyst can selectively reduce CO₂ to formate with high selectivity (≈90% faradaic efficiency), large partial current density (24.53 mA cm^-2 at -1.36 V), and long-term stability (up to 14.5 h), superior to most of the Bi-based catalysts. The hybrid Bi/In₂ O₃ interfaces of core-shell C@In₂ O₃ @Bi will stabilize the key intermediate HCOO* and suppress CO poisoning, benefiting the CO₂ RR selectivity and stability, while the internal cavity of core-shell structure will improve the reaction kinetics because of the large specific surface area and the enhancement of ion shuttle and electron transfer. Furthermore, the nano-limited domain effect of outmost carbon prevent active components from oxidation and agglomeration, helpful for stabilizing the catalyst. This work offers valuable insights into core-shell structure engineering to promote practical CO₂ conversion technology.

Photo-Induced Switching of CO2 Hydrogenation Pathway towards CH3 OH Production over Pt@UiO-66-NH2 (Co)

It is highly desired to achieve controllable product selectivity in CO₂ hydrogenation. Herein, we report light-induced switching of reaction pathways of CO₂ hydrogenation towards CH₃ OH production over actomically dispersed Co decorated Pt@UiO-66-NH₂ . CO, being the main product in the reverse water gas shift (RWGS) pathway under thermocatalysis condition, is switched to CH₃ OH via the formate pathway with the assistance of light irradiation. Impressively, the space-time yield of CH₃ OH in photo-assisted thermocatalysis (1916.3 μmol g_cat ^-1  h^-1 ) is about 7.8 times higher than that without light at 240 °C and 1.5 MPa. Mechanism investigation indicates that upon light irradiation, excited UiO-66-NH₂ can transfer electrons to Pt nanoparticles and Co sites, which can efficiently catalyze the critical elementary steps (i.e., CO₂ -to-*HCOO conversion), thus suppressing the RWGS pathway to achieve a high CH₃ OH selectivity.

Nanostructured Materials for Photothermal Carbon Dioxide Hydrogenation: Regulating Solar Utilization and Catalytic Performance

Converting carbon dioxide (CO₂) into value-added fuels or chemicals through photothermal catalytic CO₂ hydrogenation is a promising approach to alleviate the energy shortage and global warming. Understanding the nanostructured material strategies in the photothermal catalytic CO₂ hydrogenation process is vital for designing photothermal devices and catalysts and maximizing the photothermal CO₂ hydrogenation performance. In this Perspective, we first describe several essential nanomaterial design concepts to enhance sunlight absorption and utilization in photothermal CO₂ hydrogenation. Subsequently, we review the latest progress in photothermal CO₂ hydrogenation into C₁ (e.g., CO, CH₄, and CH₃OH) and multicarbon hydrocarbon (C₂₊) products. Finally, the relevant challenges and opportunities in this exciting research realm are discussed. This perspective provides a comprehensive understanding for the light-heat synergy over nanomaterials and instruction for rational photothermal catalyst design for CO₂ utilization.