Preparation of carbon supported cobalt by electrostatic adsorption of [Co(NH[subscript 3])[subscript 6]]Cl[subscript 3]
- BP Res. Cntr.
Our previous paper [L. D'Souza, L. Jiao, J.R. Regalbuto, J.T. Miller, A.J. Kropf, J. Catal. 248 (2007) 165] presented the synthesis of cobalt catalysts on carbon (Timrex) and silica supports by strong electrostatic adsorption (SEA), using a cobalt hexaamine chloride ([Co(NH{sub 3}){sub 6}]Cl{sub 3}, CoHA) precursor. The CoHA undergoes reductive deammination in an uncontrolled manner in the presence of NaOH and adsorbs as Co{sub 3}O{sub 4} on carbon with broad size distribution. The present paper extends these studies toward the end of synthesizing well-dispersed Co oxide particles in a narrow size range on carbon supports using NH{sub 4}OH. Cobalt uptake versus pH was determined in NH{sub 4}OH and NaOH basified solutions over a number of carbons with varying point of zero charge (PZC). The resulting materials were characterized by ICP, powder XRD, XAS, TPR and STEM. CoHA in the presence of NH{sub 4}OH adsorbs as well dispersed as CoO, Co{sub 3}O{sub 4} and Co(OH){sub 4}{sup 2-} depending upon the pH of the adsorption solution. These phases were undetectable by powder XRD and STEM Z-contrast imaging, but could be identified by XAS. Additionally, non-adsorbed CoHA complexes underwent transformation to [Co(NH{sub 3}){sub 5}Cl]Cl{sub 2} at pH > 11 in solution. After calcinations of 250 C, particle sizes of Co{sub 3}O{sub 4} range from 20-50 {angstrom} from NH{sub 4}OH and 50-200 {angstrom} from NaOH. Maximum metal uptake was approximately 3.3 and 2.7 {micro}mol/m{sup 2} in presence of NaOH and NH{sub 4}OH, respectively. The SEA method of preparation was compared with incipient wetness impregnation (IWI) of Co(NO{sub 3}){sub 2}{sm_bullet}6H{sub 2}O; this method yields Co{sub 3}O{sub 4} particles after 250 C calcinations which are almost as small or in one case, smaller than the calcined SEA samples. Higher metal loadings can be achieved by the SEA method by successive adsorption steps with a little variation in particle size and distribution. However, the main advantage of SEA is in forming mono- or submonolayer of different Co oxide phases on carbon surface.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1007166
- Journal Information:
- J. Catal., Vol. 254, Issue (2) ; 03, 2008; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- ENGLISH
Similar Records
Hydrothermal synthesis attempts of dawsonite-type hydroxymetalocarbonate precursor compounds for catalytic Ho, Sm, and La oxides
Structural, magnetic and catalytic properties of cobalt chromite obtained through precursor method