Effective methane utilization for either clean power generation or value-added chemical production has been a subject of growing attention worldwide for decades, yet challenges persist mostly in relation to methane activation under mild conditions. Here, we report hematite, an earth-abundant material, to be highly effective and thermally stable to catalyze methane combustion at low temperatures (<500 °C) with a low light-off temperature of 230 °C and 100% selectivity to CO 2 . The reported performance is impressive and comparable to those of precious-metal-based catalysts, with a low apparent activation energy of 17.60 kcal• mol −1 . Our theoretical analysis shows that the excellent performance stems from a tetra-iron center with an antiferromagnetically coupled iron dimer on the hematite (110) surface, analogous to that of the methanotroph enzyme methane monooxygenase that activates methane at ambient conditions in nature. Isotopic oxygen tracer experiments support a Mars van Krevelen redox mechanism where CH 4 is activated by reaction with a hematite surface oxygen first, followed by a catalytic cycle through a molecular-dioxygen-assisted pathway. Surface studies with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations reveal the evolution of reaction intermediates from a methoxy CH 3 − O−Fe, to a bridging bidentate formate b-HCOO−Fe, to a monodentate formate m-HCOO−Fe, before CO 2 is eventually formed via a combination of thermal hydrogen-atom transfer (HAT) and proton-coupled electron transfer (PCET) processes. The elucidation of the reaction mechanism and the intermediate evolutionary profile may allow future development of catalytic syntheses of oxygenated products from CH 4 in gas-phase heterogeneous catalysis.
Photocatalytic reduction of CO2 to valuable chemical fuels is of broad interest, given its potential to activate stable greenhouse CO2 using renewable energy input. We report how to choose the right metal cocatalysts in combination with the surface basicity of TiO2 to enhance their photocatalytic efficiency for CO2 photoreduction. Uniform ligand-free metal nanoparticles (NPs) of Ag, Cu, Au, Pd, and Pt, supported on TiO2, are active for CO2 photoreduction using water as an electron donor. The group XI metals show a high selectivity to CO and Ag/TiO2 is most active to produce CO at a rate of 5.2 μmol g–1 h–1. The group X metals, e.g., Pd and Pt, mainly generate hydrocarbons including methane and ethane, and Pd/TiO2 is slightly more active in methane production at a rate of 2.4 μmol g–1 h–1. The activity of these photocatalysts can be enhanced by varying the surface basicity of TiO2 with primary amines. However, proton reduction selectivity is greatly enhanced in the presence of amine except amine-modified Ag/TiO2, which shows an activity enhancement by 2.4 times solely for CO2 photoreduction as compared to that without amines without switching its selectivity to proton reduction. Using in situ infrared spectroscopy and CO stripping voltammetry, we demonstrate that the improvement of electron density and the low proton affinity of metal cocatalysts are of key importance in CO2 photoreduction. As a systematic study, our results provide a guideline on the right choice of metals in combination of the surface functionality to tune the photocatalytic efficiency of supported metal NPs on TiO2 for selective CO2 photoreduction.
Water harvesting from the atmosphere using adsorption-based technology holds great promise to solve water scarcity in arid regions. Birnessite (i.e., a layered structure MnO 2 ) can store water molecularly between its layers, providing a path for water adsorption. This work investigates the water sorption characteristic of birnessite from both thermodynamic and kinetic perspectives. The water vapor adsorption on birnessite follows a Type II sorption isotherm. Water molecules quickly adsorb to the interlayers at lower RH region values, while multilayer water−water interactions occur via hydrogen bonding at surfaces and result in condensed water at higher RH. Furthermore, birnessite features excellent solar absorptivity; the temperature can be raised by 87 °C under solar irradiation at a sun flux of ∼900 W/m 2 , providing energy to trigger partial desorption of interlayer water. According to the Do and Do model simulation, birnessite can harvest 0.07 kg of water per kilogram of sample (kg H2O /kg Sample ) per cycle at RH of 23% when the dew point temperature is set to 11 °C. Finally, a device based on the concept of sorption-based atmospheric water harvesting is built to present this application. This inexpensive water adsorption material with solar absorptivity displays an applicable promise for solving water scarcity in arid regions.
Carbon capture and storage (CCS) technologies have the potential for reducing greenhouse gas emissions and creating clean energy solutions. One of the major aspects of the CCS technology is designing energy-efficient adsorbent materials for carbon dioxide capture. In this research, using a combination of first-principles theory, synthesis, and property measurements, we explore the CO2 gas adsorption capacity of MoS2 sheets via doping with iron, cobalt, and nickel. We show that substitutional dopants act as active sites for CO2 adsorption. The adsorption performance is determined to be dependent on the type of dopant species as well as its concentration. Nickel-doped MoS2 is found to be the best adsorbent for carbon capture with a relatively high gas adsorption capacity compared to pure MoS2 and iron- and cobalt-doped MoS2. Specifically, Brunauer–Emmett–Teller (BET) measurements show that 8 atom % Ni–MoS2 has the highest surface area (51 m2/g), indicating the highest CO2 uptake relative to the other concentrations and other dopants. Furthermore, we report that doping could lead to different magnetic solutions with changing electronic structures where narrow band gaps and the semimetallic tendency of the substrate are observed and can have an influence on the CO2 adsorption ability of MoS2. Our results provide a key strategy to the characteristic tendencies for designing highly active and optimized MoS2-based adsorbent materials utilizing the least volume of catalysts for CO2 capture and conversion.
Bimetallic nanoalloys have attracted great research interest in the past decades by virtue of their tunable metal‐metal synergies. The preparation of well‐defined bimetallic nanoalloys largely relies on the use of capping ligands, which brings a great challenge to utilize the surface‐accessible active sites and/or tailor bimetallic‐support interactions. In the current paper, surface‐clean, thermally stable and monodisperse PdAu nanoalloys confined in mesoporous TiO2 (PdAu@mTiO2) were prepared using evaporation‐induced self‐assembly with two colloidal templates. The hydrogenation activity of PdAu@mTiO2 was demonstrated to be approximately 6 times higher than that of PdAu nanoalloys supported on mesoporous silica due to the bimetallic‐support interactions. Our method is expected to open up new opportunities to synthesize ligand‐free and stable bimetallic nanoalloys with tailored bimetallic‐support interactions for highly efficient catalysis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.