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Surface Treatment for Conductive 12 CaO⋅7 Al 2 O 3 Electride Powder by Rapid Thermal Annealing Processing and Its Application to Ammonia Synthesis
Author(s) -
Hayashi Fumitaka,
Kitano Masaaki,
Yokoyama Toshiharu,
Hara Michikazu,
Hosono Hideo
Publication year - 2014
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201301061
Subject(s) - annealing (glass) , materials science , sintering , metal , thermal treatment , thermal stability , catalysis , ammonia production , chemical engineering , ammonia , metallurgy , chemistry , composite material , organic chemistry , engineering
The inorganic electride [Ca 24 Al 28 O 64 ] 4+ (e − ) 4 (C12A7:e − ) has unique properties, that is, chemical stability and a low work function comparable to that of metal K. However, its surface area is low (≈1 m 2 g −1 ) because sintering occurs during high‐temperature annealing, which is needed to remove CaO layers formed by reaction with metal Ca that works as a reductant. We report a simple synthesis method for moderate‐surface‐area C12A7:e − (9–19 m 2 g −1 ) by using a rapid thermal annealing (RTA) technique. The synthesis consists of 1) high‐temperature evacuation, 2) reaction with Ca metal, and 3) RTA. The influence of these synthesis conditions was first studied to achieve both high surface area and high electron concentration. Next, C12A7:e − samples were examined as Ru catalyst supports for NH 3 synthesis. The activity of Ru‐loaded as‐prepared C12A7:e − was moderate but was increased fivefold by RTA processing prior to Ru loading as a result of surface structure reconstruction. The improvement in the Ru dispersion degree that results from the increased surface area trebled the overall activity (3550 μmol NH 3 g cat −1 h −1 at 340 °C) compared with that of conventional Ru/C12A7:e − .