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Title: Particle size effect of redox reactions for Co species supported on silica

Abstract

Conversions of chemical states during redox reactions of two silica-supported Co catalysts, which were prepared by the impregnation method, were evaluated by using an in situ XAFS technique. The addition of citric acid into the precursor solution led to the formation on silica of more homogeneous and smaller Co particles, with an average diameter of 4 nm. The supported Co{sub 3}O{sub 4} species were reduced to metallic Co via the divalent CoO species during a temperature-programmed reduction process. The reduced Co species were quantitatively oxidized with a temperature-programmed oxidation process. The higher observed reduction temperature of the smaller CoO particles and the lower observed oxidation temperature of the smaller metallic Co particles were induced by the higher dispersion of the Co oxide species, which apparently led to a stronger interaction with supporting silica. The redox temperature between CoO and Co{sub 3}O{sub 4} was found to be independent of the particle size. - Graphical abstract: Chemical state conversions of SiO{sub 2}-supported Co species and the particle size effect have been analyzed by means of in situ XAFS technique. The small CoO particles have endurance against the reduction and exist in a wide temperature range. Display Omitted - Highlights: • The conversionsmore » of the chemical state of supported Co species during redox reaction are evaluated. • In operando XAFS technique were applied to measure redox properties of small Co particles. • A small particle size affects to the redox temperatures of cobalt catalysts.« less

Authors:
; ; ; ; ; ;
Publication Date:
OSTI Identifier:
22584212
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 241; Other Information: Copyright (c) 2016 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTROSCOPY; CATALYSTS; CHEMICAL STATE; CITRIC ACID; COBALT; COBALT OXIDES; FINE STRUCTURE; OXIDATION; PARTICLE SIZE; PARTICLES; REDOX REACTIONS; SILICA; SILICON OXIDES; SOLUTIONS; STRONG INTERACTIONS; TEMPERATURE RANGE; X-RAY SPECTROSCOPY

Citation Formats

Chotiwan, Siwaruk, Tomiga, Hiroki, Katagiri, Masaki, Yamamoto, Yusaku, Yamashita, Shohei, Katayama, Misaki, and Inada, Yasuhiro, E-mail: yinada@fc.ritsumei.ac.jp. Particle size effect of redox reactions for Co species supported on silica. United States: N. p., 2016. Web. doi:10.1016/J.JSSC.2016.06.020.
Chotiwan, Siwaruk, Tomiga, Hiroki, Katagiri, Masaki, Yamamoto, Yusaku, Yamashita, Shohei, Katayama, Misaki, & Inada, Yasuhiro, E-mail: yinada@fc.ritsumei.ac.jp. Particle size effect of redox reactions for Co species supported on silica. United States. doi:10.1016/J.JSSC.2016.06.020.
Chotiwan, Siwaruk, Tomiga, Hiroki, Katagiri, Masaki, Yamamoto, Yusaku, Yamashita, Shohei, Katayama, Misaki, and Inada, Yasuhiro, E-mail: yinada@fc.ritsumei.ac.jp. Thu . "Particle size effect of redox reactions for Co species supported on silica". United States. doi:10.1016/J.JSSC.2016.06.020.
@article{osti_22584212,
title = {Particle size effect of redox reactions for Co species supported on silica},
author = {Chotiwan, Siwaruk and Tomiga, Hiroki and Katagiri, Masaki and Yamamoto, Yusaku and Yamashita, Shohei and Katayama, Misaki and Inada, Yasuhiro, E-mail: yinada@fc.ritsumei.ac.jp},
abstractNote = {Conversions of chemical states during redox reactions of two silica-supported Co catalysts, which were prepared by the impregnation method, were evaluated by using an in situ XAFS technique. The addition of citric acid into the precursor solution led to the formation on silica of more homogeneous and smaller Co particles, with an average diameter of 4 nm. The supported Co{sub 3}O{sub 4} species were reduced to metallic Co via the divalent CoO species during a temperature-programmed reduction process. The reduced Co species were quantitatively oxidized with a temperature-programmed oxidation process. The higher observed reduction temperature of the smaller CoO particles and the lower observed oxidation temperature of the smaller metallic Co particles were induced by the higher dispersion of the Co oxide species, which apparently led to a stronger interaction with supporting silica. The redox temperature between CoO and Co{sub 3}O{sub 4} was found to be independent of the particle size. - Graphical abstract: Chemical state conversions of SiO{sub 2}-supported Co species and the particle size effect have been analyzed by means of in situ XAFS technique. The small CoO particles have endurance against the reduction and exist in a wide temperature range. Display Omitted - Highlights: • The conversions of the chemical state of supported Co species during redox reaction are evaluated. • In operando XAFS technique were applied to measure redox properties of small Co particles. • A small particle size affects to the redox temperatures of cobalt catalysts.},
doi = {10.1016/J.JSSC.2016.06.020},
journal = {Journal of Solid State Chemistry},
number = ,
volume = 241,
place = {United States},
year = {Thu Sep 15 00:00:00 EDT 2016},
month = {Thu Sep 15 00:00:00 EDT 2016}
}
  • Two series of silica supported cobalt catalysts were prepared by incipient wetness impregnation, one by varying the calcination temperature (200-400{degree}C, 3 wt % Co) and the other by changing the cobalt loading (1-10 wt % Co). Examination by ESCA, XRD, and H{sub 2} chemisorption showed that Co{sub 3}O{sub 4} is the dominant phase. The cobalt phase is reduced to cobalt metal at 400{degree}C. The cobalt particle sizes obtained from ESCA correlated well with those derived from H{sub 2} chemisorption and XRD line broadening. The turnover frequency of Co/SiO{sub 2} for CO hydrogenation was invariant with cobalt dispersion in the rangemore » of 6-20% dispersion.« less
  • Monodisperse palladium particles of six distinct and controlled sizes between 4-16 nm were synthesized in a one-pot polyol process by varying the molar ratios of the two palladium precursors used, which contained palladium in different oxidation states. This difference permitted size control by regulation of the nucleation rate because low oxidation state metals ions nucleate quickly relative to high oxidation state ions. After immobilization of the Pd particles on silica by mild sonication, the catalysts were characterized by X-ray absorption spectroscopy and applied toward catalytic methanol decomposition. This reaction was determined as structure sensitive with the intrinsic activity (turnover frequency)more » increasing with increasing particle size. Moreover, observed catalytic deactivation was linked to product (carbon monoxide) poisoning. Co-feeding carbon dioxide caused the activity and the amount of deactivation to decrease substantially. A reaction mechanism based on the formation of the {pi}-bond between carbon and oxygen as the rate-limiting step is in agreement with antipathetic structure sensitivity and product poisoning by carbon monoxide.« less
  • The {sup 13}C NMR spectra of {sup 13}CO adsorbed on a 56% dispersion silica-supported Pd catalyst are found to be quite different from those reported for {sup 13}CO on a 19% dispersion Pd catalyst. The mobility of the {sup 13}CO is greatly reduced on these small Pd particles, which is interpreted as a consequence of the increase in the relative number of low-coordination, electron-deficient Pd sites such as on edges and corners and the concomitant increase in the tendency for CO to bind there in a linear fashion. This is supported by the observation that linear {sup 13}CO on thismore » catalyst has very little Knight shift due to the decrease in the local electron density at the Fermi level for these sites, while bridging {sup 13}CO on terraces is still substantially Knight shifted. Comparison of the {sup 13}C NMR and FTIR spectra shows that the linear CO extinction coefficient is approximately half that for the bridging CO. These NMR results correlate well with previous work on the dispersion dependence of the magnetic susceptibility of silica-supported Pd particles and with the IR spectra for CO adsorbed on such catalysts.« less
  • The effects of metal particle size and support material on the kinetics of the CO-O{sub 2} and CO-NO reactions over Rh have been investigated. For the CO-O{sub 2} reaction in the CO-inhibition regime, both the specific rate and the apparent activation energy were found to be virtually independent of the Rh particle size, but moderately sensitive to the nature of the support material (with the low-temperature oxidation activity decreasing in the order Rh/{alpha}-Al{sub 2}O{sub 3}.Rh/SiO{sub 2}.Rh/{theta}-Al{sub 2}O{sub 3}). The specific rate of the CO-NO reaction increased drastically with increasing Rh particle size; a 45-fold increase in specific rate was observedmore » as the Rh particle size increased from 10 to 676 {angstrom}. However, support material had only a small effect on both the activity and selectivity of Rh for the CO-NO reaction.« less
  • Rates of hydrocarbon synthesis (HS) from CO-H/sub 2/ (syngas) were measured for Fe supported on MgO (Fe/MgO) while Moessbauer effect spectroscopy (MES) was used for monitoring the structure of the metal. Three effects were observed as particle size d of H/sub 2/ prereduced Fe changed between 1 and 17 nm. First, the site-time yield of CH/sub 4/ synthesis the number of CH/sub 4/ molecules produced per CO-titrated site per second) increased by over an order of magnitude. Second, under conditions used (525 K, H/sub 2//CO = 3, atmospheric pressure), large Fe particles produced a lower fraction of C/sub 2//sup +/more » in the hydrocarbon product (C/sub 2//sup +/ selectivity) and showed a greater tendency for deactivation and loss of C/sub 2//sup +/ selectivity than small particles. Third, as reaction in syngas proceeded, the dominant phase shifted from chi-carbide to epsilon'-carbide as d decreased, and further decrease of d produced a decrease in the rate of epsilon'-carbide formation. The three trends for HS were the same qualitatively and similar quantitatively when the catalysts were converted to epsilon-nitride before reaction, instead of being used directly after reduction in H/sub 2/. However, MES showed that the epsilon-nitride structure persisted even after 20 h in reacting syngas although measurements of CH/sub 4/ evolved during reduction of used samples indicated that the surface of all catalysts was thoroughly carbided. Thus, for HS, particle size was more important than interstitials in determining activity and selectivity of supported Fe.« less