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Title: Effects of Controlled Crystalline Surface of Hydroxyapatite on Methane Oxidation Reactions

Abstract

Hydroxyapatite (HAP, Ca 10(PO 4) 6(OH) 2) has a hexagonal prismatic structure that exposes two crystalline surfaces: prism-faceted a- and basal-faceted c-surfaces. Here, the predominant exposure of c-surface was controlled, and its influences in methane oxidation reactions (combustion and oxidative coupling over HAP and lead-substituted HAP (Pb-HAP), respectively) were studied. The c-surface exposure was realized by crystal orientation in HAP-based catalyst film, which was created by an electrochemical deposition of HAP seeds on a titanium substrate, followed by hydrothermal crystallization and peeling off of the crystalline films from the substrate. In comparison to a-surface that is prevalently exposed in unoriented HAP-based catalysts, the c-surface (i.e., (002) crystalline plane) of HAP-based catalysts exhibited up to 47-fold enhancement in areal rate in both reactions. The distinct catalytic activity between these two crystalline surfaces is attributed to the preferential formation of oxide ions and vacancies on c-surfaces. The oxide ions and vacancies in turns function as actives sites for promoting methane activation and complete oxidation into CO 2. Density functional theory calculations confirmed the close relationship between different catalytic activities in c-surface of oriented and a-surface of unoriented HAP through the tendency of vacancy formation. Without the presence of vacancies, the methyl ormore » methylene group after methane activation forms ethane or ethylene via coupling. The present study explored the effects of HAP crystal orientation in methane oxidation reactions, which revealed distinct catalytic behaviors of crystal surfaces in HAP-based materials.« less

Authors:
ORCiD logo [1];  [2];  [3]; ORCiD logo [2];  [1]
  1. Univ. of Maryland, College Park, MD (United States). Dept. of Chemical and Biomolecular Engineering
  2. Kansas State Univ., Manhattan, KS (United States). Dept. of Chemical Engineering
  3. U.S. Army Research Lab., Adelphi, MD (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); Univ. of California, Oakland, CA (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1543698
Grant/Contract Number:  
AC02-05CH11231; AC02-06CH11357
Resource Type:
Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 8; Journal Issue: 5; 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; chemistry; hydroxyapatite; crystalline plane; methane conversion; density functional theory; oxygen vacancy

Citation Formats

Oh, Su Cheun, Xu, Jiayi, Tran, Dat T., Liu, Bin, and Liu, Dongxia. Effects of Controlled Crystalline Surface of Hydroxyapatite on Methane Oxidation Reactions. United States: N. p., 2018. Web. doi:10.1021/acscatal.7b04011.
Oh, Su Cheun, Xu, Jiayi, Tran, Dat T., Liu, Bin, & Liu, Dongxia. Effects of Controlled Crystalline Surface of Hydroxyapatite on Methane Oxidation Reactions. United States. doi:10.1021/acscatal.7b04011.
Oh, Su Cheun, Xu, Jiayi, Tran, Dat T., Liu, Bin, and Liu, Dongxia. Mon . "Effects of Controlled Crystalline Surface of Hydroxyapatite on Methane Oxidation Reactions". United States. doi:10.1021/acscatal.7b04011. https://www.osti.gov/servlets/purl/1543698.
@article{osti_1543698,
title = {Effects of Controlled Crystalline Surface of Hydroxyapatite on Methane Oxidation Reactions},
author = {Oh, Su Cheun and Xu, Jiayi and Tran, Dat T. and Liu, Bin and Liu, Dongxia},
abstractNote = {Hydroxyapatite (HAP, Ca10(PO4)6(OH)2) has a hexagonal prismatic structure that exposes two crystalline surfaces: prism-faceted a- and basal-faceted c-surfaces. Here, the predominant exposure of c-surface was controlled, and its influences in methane oxidation reactions (combustion and oxidative coupling over HAP and lead-substituted HAP (Pb-HAP), respectively) were studied. The c-surface exposure was realized by crystal orientation in HAP-based catalyst film, which was created by an electrochemical deposition of HAP seeds on a titanium substrate, followed by hydrothermal crystallization and peeling off of the crystalline films from the substrate. In comparison to a-surface that is prevalently exposed in unoriented HAP-based catalysts, the c-surface (i.e., (002) crystalline plane) of HAP-based catalysts exhibited up to 47-fold enhancement in areal rate in both reactions. The distinct catalytic activity between these two crystalline surfaces is attributed to the preferential formation of oxide ions and vacancies on c-surfaces. The oxide ions and vacancies in turns function as actives sites for promoting methane activation and complete oxidation into CO2. Density functional theory calculations confirmed the close relationship between different catalytic activities in c-surface of oriented and a-surface of unoriented HAP through the tendency of vacancy formation. Without the presence of vacancies, the methyl or methylene group after methane activation forms ethane or ethylene via coupling. The present study explored the effects of HAP crystal orientation in methane oxidation reactions, which revealed distinct catalytic behaviors of crystal surfaces in HAP-based materials.},
doi = {10.1021/acscatal.7b04011},
journal = {ACS Catalysis},
number = 5,
volume = 8,
place = {United States},
year = {2018},
month = {4}
}

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Table 1 Table 1: Comparison of calculated lattice parameters with previous DFT and experimental results.

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