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Title: Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition

Abstract

In the development of catalytic materials, a set of standard conditions is needed where the kinetic performance of many samples can be compared. This can be challenging when a sample set covers a broad range of activity. Precise kinetic characterization requires uniformity in the gas and catalyst bed composition. This limits the range of convecting devices to low conversion (generally <20%). While steady-state kinetics offer a snapshot of conversion, yield and apparent rates of the slow reaction steps, transient techniques offer much greater detail of rate processes and hence more information as to why certain catalyst compositions offer better performance. In this work, transient experiments in two transport regimes are compared: an advecting differential plug flow reactor (PFR) and a pure-diffusion temporal analysis of products (TAP) reactor. The decomposition of ammonia was used as a model reaction to test three simple materials: polycrystalline iron, cobalt and a bimetallic preparation of the two. These materials presented a wide range of activity and it was not possible to capture transient information in the advecting device for all samples at the same conditions while ensuring uniformity. We push the boundary for the theoretical estimates of uniformity in the TAP device and find reliablemore » kinetic measurement up to 90% conversion. However, what is more advantageous from this technique is the ability to observe the time-dependence of the reaction rate rather than just singular points of conversion and yield. For example, on the iron sample we observed reversible adsorption of ammonia and on cobalt materials we identify two routes for hydrogen production. From the time-dependence of reactants and product, the dynamic accumulation was calculated. This was used to understand the atomic distribution of H and N species regulated by the surface of different materials. When ammonia was pulsed at 550 °C, the surface hydrogen/nitrogen, (H/N), ratios that evolved for Fe, CoFe and Co were 2.4, 0.25 and 0.3 respectively. This indicates that iron will store a mixture of hydrogenated species while materials with cobalt will predominantly store NH and N. While much is already known about iron, cobalt and ammonia decomposition, the goal of this work was to demonstrate new tools for comparing materials over a wider window of conversion and with much greater kinetic detail. As a result, this provides an approach for detailed kinetic discrimination of more complex industrial samples beyond conversion and yield.« less

Authors:
 [1]; ORCiD logo [1];  [2]; ORCiD logo [1];  [3];  [3]; ORCiD logo [1]
  1. Idaho National Lab. (INL), Idaho Falls, ID (United States)
  2. Idaho State Univ., Pocatello, ID (United States)
  3. Washington Univ., St. Louis, MO (United States)
Publication Date:
Research Org.:
Idaho National Lab. (INL), Idaho Falls, ID (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1492829
Report Number(s):
INL/JOU-19-52383-Rev000
Journal ID: ISSN 2073-4344; CATACJ
Grant/Contract Number:  
AC07-05ID14517
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Catalysts
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2073-4344
Publisher:
MDPI
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Advecting differential plug flow reactor; Temporal Analysis of Products Reactor; TAP; PFR; ammonia decomposition

Citation Formats

Wang, Yixiao, Kunz, M. Ross, Siebers, Skyler, Rollins, Harry W., Gleaves, John, Yablonsky, Gregory, and Fushimi, Rebecca R. Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition. United States: N. p., 2019. Web. doi:10.3390/catal9010104.
Wang, Yixiao, Kunz, M. Ross, Siebers, Skyler, Rollins, Harry W., Gleaves, John, Yablonsky, Gregory, & Fushimi, Rebecca R. Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition. United States. doi:10.3390/catal9010104.
Wang, Yixiao, Kunz, M. Ross, Siebers, Skyler, Rollins, Harry W., Gleaves, John, Yablonsky, Gregory, and Fushimi, Rebecca R. Sat . "Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition". United States. doi:10.3390/catal9010104. https://www.osti.gov/servlets/purl/1492829.
@article{osti_1492829,
title = {Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition},
author = {Wang, Yixiao and Kunz, M. Ross and Siebers, Skyler and Rollins, Harry W. and Gleaves, John and Yablonsky, Gregory and Fushimi, Rebecca R.},
abstractNote = {In the development of catalytic materials, a set of standard conditions is needed where the kinetic performance of many samples can be compared. This can be challenging when a sample set covers a broad range of activity. Precise kinetic characterization requires uniformity in the gas and catalyst bed composition. This limits the range of convecting devices to low conversion (generally <20%). While steady-state kinetics offer a snapshot of conversion, yield and apparent rates of the slow reaction steps, transient techniques offer much greater detail of rate processes and hence more information as to why certain catalyst compositions offer better performance. In this work, transient experiments in two transport regimes are compared: an advecting differential plug flow reactor (PFR) and a pure-diffusion temporal analysis of products (TAP) reactor. The decomposition of ammonia was used as a model reaction to test three simple materials: polycrystalline iron, cobalt and a bimetallic preparation of the two. These materials presented a wide range of activity and it was not possible to capture transient information in the advecting device for all samples at the same conditions while ensuring uniformity. We push the boundary for the theoretical estimates of uniformity in the TAP device and find reliable kinetic measurement up to 90% conversion. However, what is more advantageous from this technique is the ability to observe the time-dependence of the reaction rate rather than just singular points of conversion and yield. For example, on the iron sample we observed reversible adsorption of ammonia and on cobalt materials we identify two routes for hydrogen production. From the time-dependence of reactants and product, the dynamic accumulation was calculated. This was used to understand the atomic distribution of H and N species regulated by the surface of different materials. When ammonia was pulsed at 550 °C, the surface hydrogen/nitrogen, (H/N), ratios that evolved for Fe, CoFe and Co were 2.4, 0.25 and 0.3 respectively. This indicates that iron will store a mixture of hydrogenated species while materials with cobalt will predominantly store NH and N. While much is already known about iron, cobalt and ammonia decomposition, the goal of this work was to demonstrate new tools for comparing materials over a wider window of conversion and with much greater kinetic detail. As a result, this provides an approach for detailed kinetic discrimination of more complex industrial samples beyond conversion and yield.},
doi = {10.3390/catal9010104},
journal = {Catalysts},
issn = {2073-4344},
number = 1,
volume = 9,
place = {United States},
year = {2019},
month = {1}
}

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Figures / Tables:

Figure 1 Figure 1: (A) Representative transmission electron microscope (TEM) images of the bimetallic catalyst, (B) particle size distribution (C) Co mapping, (D) Fe mapping.

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Works referenced in this record:

H2 Production via Ammonia Decomposition Using Non-Noble Metal Catalysts: A Review
journal, July 2016