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Title: Dynamic Oxygen on Surface: Catalytic Intermediate and Coking Barrier in the Modeled CO 2 Reforming of CH 4 on Ni (111)

We identify Ni-O phases as important intermediates in a model dry (CO 2) reforming of methane catalyzed by Ni (111), based on results from in operando near ambient X-ray photoelectron spectroscopy (NAP-XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). We find that under a CO 2 or CO 2-CH 4 atmosphere, the Ni-O phases exist as p(2×2) structured chemisorbed oxygen (Chem-O), epitaxial NiO (111), or oxygen-rich Ni xO y (x2O 3), depending on the chemical potential. The growth rates of the Ni-O phases have a negative correlation with temperature from 600 K to 900 K, proving that their dynamic concentrations in the reaction are not limited by CO 2 activation, but by their thermal stability. Between 300 K and 800 K (1:1 CH 4 and CO 2 mixture), oxidation by CO 2is dominant, resulting in a fully Ni-O covered surface. Between 800 K and 900 K, a partially oxidized Ni (111) exists which could greatly facilitate the effective conversion of CH 4. As CH 4 is activation-limited and dissociates mainly on metallic nickel, the released carbon species can quickly react with the adjacent oxygen (Ni-O phases) to form CO. After combining with carbon and releasing CO molecules,more » the Ni-O phases can be further regenerated through oxidation by CO 2. In this way, the Ni-O phases participate in the catalytic process, acting as an intermediate in addition to the previously reported Ni-C phases. We also reveal the carbon phobic property of the Ni-O phases, which links to the intrinsic coking resistance of the catalysts. The low dynamic coverage of surface oxygen at higher temperatures (>900 K) is inferred to be an underlying factor causing carbon aggregation. Therefore solutions based on Ni-O stabilization are proposed in developing coking resisting catalysts.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [3] ;  [5] ;  [7] ;  [8]
  1. National Univ. of Singapore (Singapore). Dept. of Physics; Singapore-Peking Univ. Research Center for a Sustainable Low-Carbon Future (Singapore)
  2. Singapore-Peking Univ. Research Center for a Sustainable Low-Carbon Future (Singapore); Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)
  3. Singapore-Peking Univ. Research Center for a Sustainable Low-Carbon Future (Singapore); National Univ. of Singapore (Singapore). Dept. of Chemistry
  4. Singapore-Peking Univ. Research Center for a Sustainable Low-Carbon Future (Singapore)
  5. Yale-NUS College (Singapore). Science Division; Princeton Univ., NJ (United States). Dept. of Chemistry
  6. Singapore-Peking Univ. Research Center for a Sustainable Low-Carbon Future (Singapore); Peking Univ., Beijing (China). College of Chemistry and Molecular Engineering
  7. Shanghai Normal Univ., Shanghai (China). Chinese Education Ministry Key Lab. of Resource Chemistry
  8. National Univ. of Singapore (Singapore). Dept. of Physics; Singapore-Peking Univ. Research Center for a Sustainable Low-Carbon Future (Singapore); National Univ. of Singapore (Singapore). Dept. of Chemistry; National Univ. of Singapore Suzhou Research Inst., Suzhou, (China)
Publication Date:
Report Number(s):
BNL-113260-2016-JA
Journal ID: ISSN 2155-5435; R&D Project: 16083/16083; KC0403020
Grant/Contract Number:
SC00112704; R143-000-542-112
Type:
Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 6; Journal Issue: 7; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Singapore National Research Foundation
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; carbon dioxide; coking; dry reforming; methane; NAP-XPS; nickel; surface oxygen
OSTI Identifier:
1336228