Dataset Information

Agglomeration Suppression of a Fe-Supported Catalyst and its Utilization for Low-Temperature Ammonia Synthesis in an Electric Field.

ABSTRACT: Fe-supported heterogeneous catalysts are used for various reactions, including ammonia synthesis, Fischer-Tropsch synthesis, and exhaust gas cleaning. For the practical use of Fe-supported catalysts, suppression of Fe particle agglomeration is the most important issue to be resolved. As described herein, we found that Al doping in an oxide support suppresses agglomeration of the supported Fe particle. Experimental and computational studies revealed two tradeoff Al doping effects: the Fe particle size decreased and remained without agglomeration by virtue of the anchoring effect of doped Al. Also, some Fe atoms anchored by Al cannot function as an active site because of bonding with oxygen atoms. Using an appropriate amount of Al doping is effective for increasing the number of active Fe sites and catalytic activity. This optimized catalyst showed high practical activity and stability for low-temperature ammonia synthesis in an electric field. The optimized catalyst of 12.5 wt % Fe/Ce0.4Al0.1Zr0.5O2-? showed the highest ammonia synthesis rate (2.3 mmol g-1 h-1) achieved to date under mild conditions (464 K, 0.9 MPa) in an electric field among the Fe catalysts reported.

SUBMITTER: Sakai R

PROVIDER: S-EPMC7114694 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Agglomeration Suppression of a Fe-Supported Catalyst and its Utilization for Low-Temperature Ammonia Synthesis in an Electric Field.

Sakai Ryuya R Murakami Kota K Mizutani Yuta Y Tanaka Yuta Y Hayashi Sasuga S Ishikawa Atsushi A Higo Takuma T Ogo Shuhei S Tsuneki Hideaki H Nakai Hiromi H Sekine Yasushi Y

ACS omega 20200317 12

Fe-supported heterogeneous catalysts are used for various reactions, including ammonia synthesis, Fischer-Tropsch synthesis, and exhaust gas cleaning. For the practical use of Fe-supported catalysts, suppression of Fe particle agglomeration is the most important issue to be resolved. As described herein, we found that Al doping in an oxide support suppresses agglomeration of the supported Fe particle. Experimental and computational studies revealed two tradeoff Al doping effects: the Fe particle ...[more]

PMID: 32258920

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Project description:Low-temperature plasma catalysis has shown promise for various chemical processes such as light hydrocarbon conversion, volatile organic compounds removal, and ammonia synthesis. Plasma-catalytic ammonia synthesis has the potential advantages of leveraging renewable energy and distributed manufacturing principles to mitigate the pressing environmental challenges of the energy-intensive Haber-Bosh process, towards sustainable ammonia production. However, lack of foundational understanding of plasma-catalyst interactions poses a key challenge to optimizing plasma-catalytic processes. Recent studies suggest electro- and photoeffects, such as electric field and charge, can play an important role in enhancing surface reactions. These studies mostly rely on using density functional theory (DFT) to investigate surface reactions under these effects. However, integration of DFT with microkinetic modeling in plasma catalysis, which is crucial for establishing a comprehensive understanding of the interplay between the gas-phase chemistry and surface reactions, remains largely unexplored. This paper presents a first-principles framework coupling DFT calculations and microkinetic modeling to investigate the role of electric field on plasma-catalytic ammonia synthesis. The DFT-microkinetic model shows more consistent predictions with experimental observations, as compared to the case wherein the variable effects of plasma process parameters on surface reactions are neglected. In particular, predictions of the DFT-microkinetic model indicate electric field can have a notable effect on surface reactions relative to other process parameters. A global sensitivity analysis is performed to investigate how ammonia synthesis pathways will change in relation to different plasma process parameters. The DFT-microkinetic model is then used in conjunction with active learning to systematically explore the complex parameter space of the plasma-catalytic ammonia synthesis to maximize the amount of produced ammonia while inhibiting reactions dissipating energy, such as the recombination of H2 through gas-phase H radicals and surface-adsorbed H. This paper demonstrates the importance of accounting for the effects of electric field on surface reactions when investigating and optimizing the performance of plasma-catalytic processes.

Project description:Ammonia is an important feedstock for producing fertiliser and is also a potential energy carrier. However, the process currently used for ammonia synthesis, the Haber-Bosch process, consumes a huge amount of energy; therefore the development of new catalysts for synthesising ammonia at a high rate under mild conditions (low temperature and low pressure) is necessary. Here, we show that Ru/La0.5Ce0.5O1.75 pre-reduced at an unusually high temperature (650 °C) catalysed ammonia synthesis at extremely high rates under mild conditions; specifically, at a reaction temperature of 350 °C, the rates were 13.4, 31.3, and 44.4 mmol g-1 h-1 at 0.1, 1.0, and 3.0 MPa, respectively. Kinetic analysis revealed that this catalyst is free of hydrogen poisoning under the conditions tested. Electron energy loss spectroscopy combined with O2 absorption capacity measurements revealed that the reduced catalyst consisted of fine Ru particles (mean diameter < 2.0 nm) that were partially covered with partially reduced La0.5Ce0.5O1.75 and were dispersed on a thermostable support. Furthermore, Fourier transform infrared spectra measured after N2 addition to the catalyst revealed that N2 adsorption on Ru atoms that interacted directly with the reduced La0.5Ce0.5O1.75 weakened the N 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 N bond and thus promoted its cleavage, which is the rate-determining step for ammonia synthesis. Our results indicate that high-temperature pre-reduction of this catalyst, which consists of Ru supported on a thermostable composite oxide with a cubic fluorite structure and containing reducible cerium, resulted in the formation of many sites that were highly active for N2 reduction by hydrogen.

Dataset Information

Agglomeration Suppression of a Fe-Supported Catalyst and its Utilization for Low-Temperature Ammonia Synthesis in an Electric Field.

Publications

Agglomeration Suppression of a Fe-Supported Catalyst and its Utilization for Low-Temperature Ammonia Synthesis in an Electric Field.

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