Title: Effects of Sodium and Tungsten Promoters on Mg₆MnO₈-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 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, butmore » 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).« less

Authors:

Yusuf, Seif ^[1]; Neal, Luke ^[1]; Bao, Zhenghong ^[2]; Wu, Zili  ^[2];

• Search DOE PAGES for author "Wu, Zili"
• Search DOE PAGES for ORCID "0000-0002-4468-3240"

Li, Fanxing  ^[1]

• Search DOE PAGES for author "Li, Fanxing"
• Search DOE PAGES for ORCID "0000-0002-2580-0421"

---

+ Show Author Affiliations

1. North Carolina State Univ., Raleigh, NC (United States)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Publication Date:

Wed Feb 27 00:00:00 EST 2019

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); RAPID Manufacturing Institute, New York, NY (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1509538

Alternate Identifier(s):

OSTI ID: 1642375

Grant/Contract Number:  

AC05-00OR22725; EE0007888

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; oxidative dehydrogenation; chemical looping; redox catalyst; oxygen carrier