Carbon Dioxide Reduction using Supported Catalysts and Metal-Modified Carbides

To sustain future population and economic growth, the global energy supply is expected to increase by 60% by 2040, but the associated CO₂ emissions are a major concern. Converting CO2 into a commodity through a CO₂-neutral process has the potential to create a sustainable carbon energy economy; however, the high stability of CO₂ requires the discovery of active, selective and stable catalysts. To initially probe the performance of catalysts for CO₂ reduction, CO₂ is activated with H₂, which produces CO and CH₄ as the primary products. For this study, CO is desired for its ability to be used in the Fischer-Tropsch process, while CH₄ is undesired because of its low volumetric energy density and abundance. Precious bimetallic catalysts synthesized on a reducible support (CeO₂) show higher activity than on an irreducible support (γ-Al₂O₃) and the selectivity, represented as CO:CH₄ ratio, is correlated to electronic properties of the supported catalysts with the surface d-band center value of the metal component. Because the high cost of precious metals is unsuitable for a large-scale CO₂ conversion process, further catalyst development for CO₂ reduction focuses on active, selective and low-cost materials. Molybdenum carbide (Mo₂C) outperforms precious bimetallic catalysts and is highly active and selective for CO₂ conversion to CO. These results are further extended to other transition metal carbides (TMCs), which are found to be a class of promising catalysts and their activity is correlated with oxygen binding energy (OBE) and reducibility as shown by density functional theory (DFT) calculations and in-situ measurements. Because TMCs are made from much more abundant elements than precious metals, the catalysts can be manufactured at a much lower cost, which is critical for achieving a substantial reduction of CO₂ levels. In the aforementioned examples, sustainable CO₂ reduction requires renewable H₂, 95% of which is currently produced from hydrocarbon based-feedstocks, resulting in CO₂ emissions as a byproduct. Alternatively, CO₂ can be reduced with ethane from shale gas, which produces either synthesis gas (CO + H₂) or ethylene with high selectivity. Pt/CeO₂ is a promising catalyst to produce synthesis gas, while Mo₂C based materials preserve the C-C bond of ethane to produce ethylene. Ethylene and higher olefins are desirable for their high demand as commodity chemicals; therefore, future studies into CO₂ reduction must identify new low-cost materials that are active and stable with higher selectivity toward the production of light olefins

Bayesian Optimization of Catalysts With In-context Learning

Large language models (LLMs) are able to do accurate classification with zero or only a few examples (in-context learning). We show a prompting system that enables regression with uncertainty for in-context learning with frozen LLM (GPT-3, GPT-3.5, and GPT-4) models, allowing predictions without features or architecture tuning. By incorporating uncertainty, our approach enables Bayesian optimization for catalyst or molecule optimization using natural language, eliminating the need for training or simulation. Here, we performed the optimization using the synthesis procedure of catalysts to predict properties. Working with natural language mitigates difficulty synthesizability since the literal synthesis procedure is the model's input. We showed that in-context learning could improve past a model context window (maximum number of tokens the model can process at once) as data is gathered via example selection, allowing the model to scale better. Although our method does not outperform all baselines, it requires zero training, feature selection, and minimal computing while maintaining satisfactory performance. We also find Gaussian Process Regression on text embeddings is strong at Bayesian optimization. The code is available in our GitHub repository: https://github.com/ur-whitelab/BO-LIF

Nanocrystalline Mo2C as a Bifunctional Water Splitting Electrocatalyst

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Mo2C is a well-known low cost catalyst for the hydrogen evolution reaction (HER), but the other water splitting half reaction, the oxygen evolution reaction (OER), has not been previously reported. To investigate both reactions and the origin of the catalytic sites, four synthesis methods were employed to prepare hexagonal Fe2N type Mo2C. A comparison of the HER activities in acidic and alkaline electrolyte and OER activities in alkaline electrolyte revealed that changes in synthesis route leads to morphological and surface composition variations resulting in different catalytic activities. In general, the trend in HER and OER activities show remarkably similar trends across the carbides synthesized via different routes irrespective of either electrolyte employed or reaction probed for electrocatalytic activities. Mo2C templated on multiwalled carbon nanotubes demonstrated the highest bifunctional catalytic activities, as well as superior electrochemical stability for both HER and OER. The writing's on the (multi)wall: Molybdenum carbide templated on multiwalled carbon nanotube is an excellent bifunctional electrocatalyst for HER catalyst in acid and base, and OER in base

Kinetic studies of CO2 methanation over a Ni/γ-Al2O3 catalyst using a batch reactor

The methanation of CO2 was investigated over a wide range of partial pressures of products and reactants using a gradientless, spinning-basket reactor operated in batch mode. The rate and selectivity of CO2 methanation, using a 12 wt% Ni/γ–Al2O3 catalyst, were explored at temperatures 453–483 K and pressures up to 20 bar. The rate was found to increase with increasing partial pressures of H2 and CO2 when the partial pressures of these reactants were low; however, the rate of reaction was found to be insensitive to changes in the partial pressures of H2 and CO2 when their partial pressures were high. A convenient method of determining the effect of H2O on the rate of reaction was also developed using the batch reactor and the inhibitory effect of H2O on CO2 methanation was quantified. The kinetic measurements were compared with a mathematical model of the reactor, in which different kinetic expressions were explored. The kinetics of the reaction were found to be consistent with a mechanism in which adsorbed CO2 dissociated to adsorbed CO and O on the surface of the catalyst with the rate-limiting step being the subsequent dissociation of adsorbed CO

Sunlight-assisted hydrogenation of CO2 into ethanol and C2+ hydrocarbons by sodium-promoted Co@C nanocomposites

[EN] The hydrogenation of CO2 into hydrocarbons promoted by the action of sunlight has been studied on Co nanoparticles covered by thin carbon layers. In particular, nearly 100% selectivity to hydrocarbons is obtained with increased selectivities towards C2 + hydrocarbons and alcohols (mainly ethanol) when using nanostructured materials comprising metallic cobalt nanoparticles, carbon layers, and sodium as promoter (NaCo@C). In the contrary, larger amount of CH4 and lower selectivity to C2 + hydrocarbons and alcohols were obtained in the conventional thermal catalytic process. When using Co@C nanoparticles in the absence of Na or bare Co3O4 as catalyst, methane is essentially the main product (selectivity > 96%). Control experiments in the presence of methanol as a hole scavenger suggest the role of light in generating charges by photon absorption as promoting factor. The reaction mechanism for photoassisted CO2 hydrogenation on the Co-based catalysts was investigated by near ambient-pressure X-ray photoelectron (AP-XPS) and in situ Raman spectroscopies, which provided information on the role of light and Na promoter in the modulation of product distribution for CO2 hydrogenation. Spectroscopic studies suggested that surface CO2 dissociation to CO, the stabilization of CO adsorbed on the surface of Na-Co@C catalyst and the easy desorption of reaction products is a key step for photothermal CO2 hydrogenation to ethanol and C2 + hydrocarbons.L.L. thanks ITQ for providing a contract. A.V.P. thanks the Spanish Government (Agencia Estatal de Investigacion) and the European Union (European Regional Development Fund) for a grant for young researchers (CTQ2015-74138-JIN, AEI/FEDER/UE). J.C. thanks the Spanish Government-MINECO for a "Severo Ochoa" grant (BES-2015-075748). The AP-XPS experiments were performed at NAPP endstation of CIRCE beamline at ALBA Synchrotron with the collaboration of ALBA staff. The authors also thank the Microscopy Service of UPV for kind help on FESEM, TEM and STEM measurements. Financial supports from the Spanish Government-MINECO through "Severo Ochoa" (SEV-2016-0683) program are also gratefully acknowledged.Liu, L.; Puga, AV.; Cored-Bandrés, J.; Concepción Heydorn, P.; Pérez-Dieste, V.; García Gómez, H.; Corma Canós, A. (2018). Sunlight-assisted hydrogenation of CO2 into ethanol and C2+ hydrocarbons by sodium-promoted Co@C nanocomposites. Applied Catalysis B Environmental. 235:186-196. https://doi.org/10.1016/j.apcatb.2018.04.060S18619623