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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Photocatalytic degradation of organic pollutants coupled with simultaneous photocatalytic H 2 evolution over graphene quantum dots/Mn-N-TiO 2 /g-C 3 N 4 composite catalysts: Performance and mechanism
Graphene quantum dots/Mn-N-TiO 2 /g-C 3 N 4 (GQDs/TCN) composite photocatalysts have been designed, synthesized and characterized by XRD, SEM, TEM, Raman, BET, and XPS. The photodegradation of organic pollutants (p-nitrophenol, diethyl phthalate and ciprofloxacin, called as 4-NP, CIP and DEP, respectively) coupled with simultaneous photocatalytic production of hydrogen was successfully achieved using the GQDs/TCN catalysts. The 5%GQDs/TCN-0.4 sample shows the best photocatalytic hydrogen production and organic pollutant degradation rate under simulated solar irradiation in the simultaneous photocatalytic oxidation and reduction system. Furthermore, the photocatalytic H 2 evolution rates in the solution of 4-NP, CIP and DEP are all larger than that in pure water system over the 5%GQDs/TCN-0.4 catalyst. And the H 2 evolution rate in the solution of 4-NP is smaller than that in the solutions of CIP and DEP. Accordingly, the photodegradation rate of 4-NP is larger than that of CIP and DEP. The analyses of density functional theory and liquid chromatography mass spectrometry indicate that some photogenerated electrons were used in the photodegradation process of 4-NP but not in that of CIP and DEP. And it leads to the photocatalytic rate of H 2 evolution in the 4-NP solution smaller than that in the solution of CIP and DEP. For the first time, the present work illuminates the photocatalytic enhancement of the GQDs/TCN-0.4 catalyst and the mechanism of the effect of different organic pollutants on photocatalytic H 2 evolution.
An ultrastable heterostructured oxide catalyst based on high-entropy materials: A new strategy toward catalyst stabilization via synergistic interfacial interaction
Designing high–performance catalysts that can stabilize catalytic active sites against sintering to deactivation at temperature higher than 900°C is significant but challenging. In this work, we report a new strategy to obtain a transition metal oxide catalyst with high temperature stability for CO oxidation. This is achieved through a synergistic interfacial interaction at the interface of a heterostructure between high– entropy oxides (HEO, high temperature stability) and CuCeO x (catalytic site). The catalytic site (CuCeO x ) for CO oxidation is realized by dissolving an amount of Cu species in HEO into CeO 2 via an entropy–driven mechanochemical process. In situ XRD and HAADF–STEM have confirmed the high temperature stability of the heterostructure CuCeO x –HEO, which can remain its CO oxidation catalytic activity at elevated temperatures. It should be expected that this innovative will offer the potential to the synthesis of catalysts with high temperature stability in industry.
Kinetic modeling and transient DRIFTS–MS studies of CO2 methanation over Ru/Al2O3 catalysts
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Quinone-mediated electrochemical O2 reduction accessing high power density with an off-electrode heterogeneous catalyst
New methods for interconversion of electrical and chemical energy are crucial to address emerging challenges in renewable energy storage and conversion. Dissolved redox mediators provide an effective means to transport electrons (and protons) between an electrode and catalysts that are not in direct physical contact with an electrode. Mediators are widely implemented in biofuel cells, but such devices typically exhibit low power densities. Here, we report the development of a tetrasubstituted quinone mediator that exhibits excellent stability under strongly acidic conditions and supports electrochemical reduction of O2 at an off-electrode heterogeneous cobalt catalyst contained within a packed-bed reactor. Efficient oxidation of the hydroquinone by O2 in the reactor provides the basis for mediator regeneration, and an integrated “flow cathode” system supports high fuel-cell power densities. These results establish the combination of organic mediators with off-electrode heterogeneous catalysts as a versatile platform for development of new electrode-driven chemical redox transformations.
An atomistic picture is worth a thousand words: New details on supported molecular catalysts
Here, homogeneous and heterogeneous catalysts have advantages and disadvantages. Molecular catalysts supported on heterogeneous materials have the potential to combine the advantages of both fields. Jabbour et al. report a detailed study of the 3D structure of an Ir-catalyst on silica.
Palladized cells as suspension catalyst and electrochemical catalyst for reductively degrading aromatics contaminants: Roles of Pd size and distribution
The palladized cell (Pd-cell) could be used as an efficient catalyst in catalyzing the degradations of a wide variety of environmental contaminants. Nevertheless, when the Pd NPs associate with the bacteria, the catalytic activity likely significantly affected by the biomass. Quantitative indicators that characterize of Pd-cell are necessary and little attention has been paid to investigate how the catalytic efficiency of Pd-cell is affected by the size and distribution of Pd NPs. To fill this gap, we explored the roles of the above-mentioned key factors on the performance of Pd-cell in catalyzing the degradations of two aromatic contaminants (nitrobenzene and p-chlorophenol) in two commonly used scenarios: (1) using Pd-cell as suspended catalyst in solution and (2) using Pd-cell as electrocatalyst directly coated on electrode. In scenario (1), the relationship of exposing area to Pd particle size and distribution factors was established. Based on theoretical estimation and catalytic performance analysis, the results indicated that adjusting the exposing area to a large value (9.3 ± 0.1 × 10 5 nm 2 mg -1 Pd) was extremely effective for improving the catalytic activity of Pd-cell used as a suspension catalyst. In scenario (2), our results showed that the best electrocatalytic performances were achieved on the electrode decorated with Pd-cells with the largest NP size (54.3 ± 16.4 nm), which exerted maximum electrochemical active surface area (10.6 m 2 g -1 ) as well as favorable conductivity. The coverage of deposited Pd NPs (>95%) on the cell surface played a crucial role in boosting the conductivity of biocatalyst, thus determining the possibility of Pd-cell as an efficient electrocatalyst. The findings of this study provide a guidance for the synthesis and application of Pd-cell, which enables the design of Pd-cell to be suitable for different catalysis systems with high catalytic performance.
Insights into Supported Subnanometer Catalysts Exposed to CO via Machine-Learning-Enabled Multiscale Modeling
Subnanometer catalysts offer high noble metal utilization and superior performance for several reactions. However, understanding their structures and properties on an atomic scale under working conditions is challenging due to the large configurational space. Here, we introduce an efficient multiscale framework to predict their stability exposed to an adsorbate. The framework integrates a comprehensive toolset including density functional theory (DFT) calculations, cluster expansion, machine learning, and structure optimization. The end-to-end machine-learning workflow guides DFT data generation and enables significant computational acceleration. We demonstrate the approach for CO-adsorbed Pdn (n = 1–55) clusters on CeO 2 (111). Simulation results reveal that CO can facilitate restructuring by stabilizing smaller planar structures and bilayer structures of specific intermediate sizes, consistent with experimental reports. Metal–support interactions, preferential CO adsorption, and metal nuclearity and structure control catalyst stability. As a result, the framework allows automatic discovery of stable catalyst structures and a systematic strategy to exploit properties in the subnanometer scale.
Integration of an Oxidation Catalyst with Pd/Zeolite-Based Passive NOx Adsorbers: Impacts on Degradation Resistance and Desorption Characteristics
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Covalent Functionalization of Silicon with Plasma-Grown “Fuzzy” Graphene: Robust Aqueous Photoelectrodes for CO 2 Reduction by Molecular Catalysts
Carbon electrodes are ideal for electrochemistry with molecular catalysts, exhibiting facile charge transfer and good stability. Yet for solar-driven catalysis with semiconductor light absorbers, stable semiconductor/carbon interfaces can be difficult to achieve, and carbon’s high optical extinction means it can only be used in ultrathin layers. Here, we demonstrate a plasma-enhanced chemical vapor deposition process that achieves well-controlled deposition of out-of-plane “fuzzy” graphene (FG) on thermally oxidized Si substrates. The resulting Si|FG interfaces possess a silicon oxycarbide (SiOC) interfacial layer, implying covalent bonding between Si and the FG film that is consistent with the mechanical robustness observed from the films. The FG layer is uniform and tunable in thickness and optical transparency by deposition time. Using p-type Si|FG substrates, noncovalent immobilization of cobalt phthalocyanine (CoPc) molecular catalysts was employed for the photoelectrochemical reduction of CO 2 in aqueous solution. The Si|FG|CoPc photocathodes exhibited good catalytic activity, yielding a current density of ∼1 mA/cm 2 , Faradaic efficiency for CO of ∼70% (balance H 2 ), and stable photocurrent for at least 30 h at −1.5 V vs Ag/AgCl under 1-sun illumination. Furthermore, the results suggest that plasma-deposited FG is a robust carbon electrode for molecular catalysts and suitable for further development of aqueous-stable Si photocathodes for CO 2 reduction.
Enhancing Oxygen Reduction Performance of Pt Monolayer Catalysts by Pd(111) Nanosheets on WNi Substrates
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Achieving Product Control in Furfural Hydrogenation Using Intermetallic Catalysts
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Calculations of CO Oxidation over a Au/TiO 2 Catalyst: A Study of Active Sites, Catalyst Deactivation, and Moisture Effects
The reaction mechanism of CO oxidation on Au/TiO 2 catalysts remains elusive. Here, we employ density functional theory calculations to gain an understanding of several important aspects of the system, including CO adsorption, the active oxygen species, catalyst deactivation, and the promoting effect of moisture on catalytic activity. Distinct from previous theoretical studies, which tend to address these questions individually, here we construct a model of the catalytic system which can address all of the issues mentioned. For this, we have considered the complex interactions among reactants, products, and catalysts under reaction conditions. The main findings of our present study are (1) the Au/TiO 2 interface boundary can be easily oxidized, (2) CO adsorption on oxidized Au results in the formation of O–Au–CO species, (3) surface lattice oxygen on a TiO 2 support is the active oxygen species, (4) CO 2 binds strongly on the O top /Ti 5c site, forming carbonate that blocks the active site, and finally (5) water can accelerate O 2 dissociation and carbonate decomposition. The results of our theoretical model are compared with existing experimental observations and found to be largely consistent with them.
Combining CO 2 reduction with propane oxidative dehydrogenation over bimetallic catalysts
In this paper, the inherent variability and insufficiencies in the co-production of propylene from steam crackers has raised concerns regarding the global propylene production gap and has directed industry to develop more on-purpose propylene technologies. The oxidative dehydrogenation of propane by CO 2 (CO 2 -ODHP) can potentially fill this gap while consuming a greenhouse gas. Non-precious FeNi and precious NiPt catalysts supported on CeO 2 have been identified as promising catalysts for CO 2 -ODHP and dry reforming, respectively, in flow reactor studies conducted at 823 K. In-situ X-ray absorption spectroscopy measurements revealed the oxidation states of metals under reaction conditions and density functional theory calculations were utilized to identify the most favorable reaction pathways over the two types of catalysts.
Decoding reactive structures in dilute alloy catalysts
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