TY - JOUR

T1 - Internal field 59Co NMR study of cobalt-iron nanoparticles during the activation of CoFe2/CaO catalyst for carbon nanotube synthesis

AU - Andreev, Andrey S.

AU - Krasnikov, Dmitry V.

AU - Zaikovskii, Vladimir I.

AU - Cherepanova, Svetlana V.

AU - Kazakova, Mariya A.

AU - Lapina, Olga B.

AU - Kuznetsov, Vladimir L.

AU - d'Espinose de Lacaillerie, Jean Baptiste

N1 - Publisher Copyright: © 2017 Elsevier Inc.

PY - 2018/2/1

Y1 - 2018/2/1

N2 - CoFe2/CaO catalysts for multi-walled carbon nanotubes (MWCNT) were characterized during the activation period (T = 670 °C; C2H4/Ar = 1:1, 400 sccm) by internal field 59Co nuclear magnetic resonance. During this induction period, although C2H4 is already reacting, the MWCNT yield remains negligible. The NMR spectra of the catalysts revealed the occurrence of several structural and magnetic species. They were not detectable by conventional X-ray diffraction but the heterogeneity of the metal particles was corroborated by high-resolution transmission electronic microscopy coupled with energy dispersive X-ray spectroscopy. Two samples quenched at different activation time contained, beside non-reacted pure metal Co particles, strong and weak ferromagnetic alloys. During activation, the pure Co metal content dropped and an increase of the ordering of the cobalt-iron alloy in the catalyst was evidenced thus revealing a multistage activation mechanism for the reaction. We propose this ordering process during the induction period to be an intermediate step between the strong ferromagnetic Co rich alloy and the weak ferromagnetic Fe rich one and that it favors the onset of MWCNTs growth.

AB - CoFe2/CaO catalysts for multi-walled carbon nanotubes (MWCNT) were characterized during the activation period (T = 670 °C; C2H4/Ar = 1:1, 400 sccm) by internal field 59Co nuclear magnetic resonance. During this induction period, although C2H4 is already reacting, the MWCNT yield remains negligible. The NMR spectra of the catalysts revealed the occurrence of several structural and magnetic species. They were not detectable by conventional X-ray diffraction but the heterogeneity of the metal particles was corroborated by high-resolution transmission electronic microscopy coupled with energy dispersive X-ray spectroscopy. Two samples quenched at different activation time contained, beside non-reacted pure metal Co particles, strong and weak ferromagnetic alloys. During activation, the pure Co metal content dropped and an increase of the ordering of the cobalt-iron alloy in the catalyst was evidenced thus revealing a multistage activation mechanism for the reaction. We propose this ordering process during the induction period to be an intermediate step between the strong ferromagnetic Co rich alloy and the weak ferromagnetic Fe rich one and that it favors the onset of MWCNTs growth.

KW - Co NMR

KW - Activation

KW - Catalysts

KW - Cobalt-iron alloy

KW - Induction period

KW - Multi-walled carbon nanotubes

KW - METAL-CATALYSTS

KW - NUCLEAR-MAGNETIC-RESONANCE

KW - BINARY FE

KW - HYPERFINE FIELDS

KW - POLYMERIZABLE COMPLEX METHOD

KW - SHORT-RANGE ORDER

KW - CO ALLOYS

KW - GROWTH

KW - FISCHER-TROPSCH SYNTHESIS

KW - IN-SITU

KW - Co-59 NMR

UR - http://www.scopus.com/inward/record.url?scp=85037678185&partnerID=8YFLogxK

U2 - 10.1016/j.jcat.2017.11.025

DO - 10.1016/j.jcat.2017.11.025

M3 - Article

AN - SCOPUS:85037678185

VL - 358

SP - 62

EP - 70

JO - Journal of Catalysis

JF - Journal of Catalysis

SN - 0021-9517

ER -