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Title: Effects of Sodium and Tungsten Promoters on Mg 6MnO 8-Based Core–Shell Redox Catalysts for Chemical Looping—Oxidative Dehydrogenation of Ethane

Abstract

The present study investigates the effect of sodium and tungsten promoters on Mg 6MnO 8-based redox catalysts in a chemical looping oxidative dehydrogenation (CL-ODH) scheme. CL-ODH has the potential to significantly lower energy consumption and CO 2/NO x emissions for ethylene production compared with conventional steam cracking. Sodium tungstate (Na 2WO 4) was previously shown to be an effective promoter for Mg 6MnO 8-based redox catalysts. Overall, the CL-ODH reaction proceeds via parallel gas-phase cracking of ethane and selective combustion of H 2 on the surface of the Na 2WO 4-promoted redox catalyst. Reaction testing indicates that both Na and W are necessary to form Na 2WO 4 and to achieve high ethylene selectivity. A Na:W ratio lower than 2:1 lead to significant formation of additional mixed tungsten oxide phases and decreases ethylene selectivity. Further characterizations based on low-energy ion scattering (LEIS) and differential scanning calorimetry (DSC) indicate that the NaW promoter forms a molten shell around the Mg6MnO8 redox catalyst. Methanol TPSR and in situ DRIFTS experiments indicate that the promoter significantly suppresses the number of basic sites on Mg 6MnO 8. 18O– 16O exchange experiments reveal that the promoter decreases the rate of oxygen exchange. O 2 cofeedmore » studies indicate that below the melting temperature of Na 2WO 4, H 2 and CO conversions are both inhibited, but above the melting temperature, H 2 combustion significantly increased while CO combustion is still inhibited. On the basis of extensive characterizations, it was determined that H 2 is primarily combusted at the gas–Na 2WO 4 molten shell interface via redox reactions of the tungsten salt, likely between the WO 4 2– (tungstate) and WO 3 (tungsten bronze).« less

Authors:
 [1];  [1];  [2]; ORCiD logo [2]; ORCiD logo [1]
  1. North Carolina State Univ., Raleigh, NC (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1509538
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 9; Journal Issue: 4; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Yusuf, Seif, Neal, Luke, Bao, Zhenghong, Wu, Zili, and Li, Fanxing. Effects of Sodium and Tungsten Promoters on Mg6MnO8-Based Core–Shell Redox Catalysts for Chemical Looping—Oxidative Dehydrogenation of Ethane. United States: N. p., 2019. Web. doi:10.1021/acscatal.9b00164.
Yusuf, Seif, Neal, Luke, Bao, Zhenghong, Wu, Zili, & Li, Fanxing. Effects of Sodium and Tungsten Promoters on Mg6MnO8-Based Core–Shell Redox Catalysts for Chemical Looping—Oxidative Dehydrogenation of Ethane. United States. doi:10.1021/acscatal.9b00164.
Yusuf, Seif, Neal, Luke, Bao, Zhenghong, Wu, Zili, and Li, Fanxing. Wed . "Effects of Sodium and Tungsten Promoters on Mg6MnO8-Based Core–Shell Redox Catalysts for Chemical Looping—Oxidative Dehydrogenation of Ethane". United States. doi:10.1021/acscatal.9b00164.
@article{osti_1509538,
title = {Effects of Sodium and Tungsten Promoters on Mg6MnO8-Based Core–Shell Redox Catalysts for Chemical Looping—Oxidative Dehydrogenation of Ethane},
author = {Yusuf, Seif and Neal, Luke and Bao, Zhenghong and Wu, Zili and Li, Fanxing},
abstractNote = {The present study investigates the effect of sodium and tungsten promoters on Mg6MnO8-based redox catalysts in a chemical looping oxidative dehydrogenation (CL-ODH) scheme. CL-ODH has the potential to significantly lower energy consumption and CO2/NOx emissions for ethylene production compared with conventional steam cracking. Sodium tungstate (Na2WO4) was previously shown to be an effective promoter for Mg6MnO8-based redox catalysts. Overall, the CL-ODH reaction proceeds via parallel gas-phase cracking of ethane and selective combustion of H2 on the surface of the Na2WO4-promoted redox catalyst. Reaction testing indicates that both Na and W are necessary to form Na2WO4 and to achieve high ethylene selectivity. A Na:W ratio lower than 2:1 lead to significant formation of additional mixed tungsten oxide phases and decreases ethylene selectivity. Further characterizations based on low-energy ion scattering (LEIS) and differential scanning calorimetry (DSC) indicate that the NaW promoter forms a molten shell around the Mg6MnO8 redox catalyst. Methanol TPSR and in situ DRIFTS experiments indicate that the promoter significantly suppresses the number of basic sites on Mg6MnO8. 18O–16O exchange experiments reveal that the promoter decreases the rate of oxygen exchange. O2 cofeed studies indicate that below the melting temperature of Na2WO4, H2 and CO conversions are both inhibited, but above the melting temperature, H2 combustion significantly increased while CO combustion is still inhibited. On the basis of extensive characterizations, it was determined that H2 is primarily combusted at the gas–Na2WO4 molten shell interface via redox reactions of the tungsten salt, likely between the WO42– (tungstate) and WO3– (tungsten bronze).},
doi = {10.1021/acscatal.9b00164},
journal = {ACS Catalysis},
number = 4,
volume = 9,
place = {United States},
year = {2019},
month = {2}
}

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This content will become publicly available on February 27, 2020
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