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Synthetic fayalite Fe 2 SiO 4 by kinetically controlled reaction between hematite and silicon carbide
Author(s) -
Pinto Rui G.,
Yaremchenko Aleksey A.,
Baptista Miguel F.,
Tarelho Luís A. C.,
Frade Jorge R.
Publication year - 2019
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16412
Subject(s) - fayalite , hematite , wüstite , reactivity (psychology) , carbide , chemistry , chemical engineering , chemical looping combustion , silicon carbide , oxygen , metal , mineralogy , materials science , inorganic chemistry , olivine , organic chemistry , medicine , alternative medicine , pathology , engineering
The present work explores the preparation of fayalite α‐Fe 2 SiO 4 , the iron‐rich end‐member of the olivine solid‐solution series, as a tar removal catalyst for biomass gasification. The synthetic procedure was developed starting from the stoichiometric mixture of hematite and micrometer size silicon carbide and employing thermal treatments in controlled atmospheres at 1000‐1100°C supported by thermodynamic modeling to assess the required redox conditions. The treatments in dry and humidified inert gas yielded phase mixtures containing metallic Fe as one of the main phases, thus emphasizing a shortage of oxygen supply. XRD and TGA studies of precursor mixtures on heating in dry CO 2 demonstrated a multistep mechanism of the overall reaction including (a) fast reactivity between silicon carbide and hematite at ~920°C with formation of metallic Fe and amorphous silica followed by (b) formation of fayalite involving oxygen supplied in the form of CO 2 and competing with (c) over‐oxidation to thermodynamically favorable Fe 3 O 4 +SiO 2 mixture. Comparative studies of reactivity in powdered and pelletized samples emphasized the importance of the kinetic factor in the formation of Fe 2 SiO 4 while preventing further oxidation. The preferential formation of fayalite in the CO 2 atmosphere is shown to be favored by shorter treatments of compacted samples at higher temperatures. The procedure was designed (2‐step heating to 1100°C in CO 2 followed by fast cooling) for the preparation of pelletized fayalite α‐Fe 2 SiO 4 catalyst with only minor traces of surface over‐oxidation which can be suppressed by adding 10 vol.% of forming gas to CO 2 flow.