Available online at www.sciencedirect.com Colloids and Surfaces A: Physicochem. Eng. Aspects 320 (2008) 123–129 Schiff base complex sol–gel method for LaCoO 3 perovskite preparation with high-adsorbed oxygen Attera Worayingyong ∗ , Praewpilin Kangvansura, Sutasinee Kityakarn Department of Chemistry, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand Received 14 July 2007; received in revised form 30 December 2007; accepted 29 January 2008 Available online 7 February 2008 Abstract A novel Schiff base complex sol–gel method has been used to prepare LaCoO 3 producing high ratios of adsorbed (or surface) oxygen () to lattice oxygen (). The as-prepared gels, characterized by Fourier transform infrared spectroscopy (FTIR), showed that both lanthanum and cobalt ions were complexed before calcinations. IR spectra revealed that CO 3 2- and NO 3 - presented on the sample surfaces during heat treatment. High-resolution transmission electron microscopic (HRTEM) images of all samples showed resolved lattice fringes with the inter-planar spacing 0.37–0.39 nm of the (0 1 2) plane in hexagonal perovskite. BET surface areas of LaCoO 3 nano-crystals were 11.7–18.6 m 2 /g. Ratios of adsorbed (or surface) oxygen () to lattice oxygen () quantified by X-ray photoemission spectroscopy showed that LaCoO 3 prepared by the Schiff base complex method produced higher ratios when bases had higher nitrogen content in molecules. Carbonate and nitrate which were resulting from the oxidation of functional groups in the Schiff base complex, can produce gaseous compounds and leave vacant sites for oxygen in the gas phase to adsorb. © 2008 Elsevier B.V. All rights reserved. Keywords: Schiff base; LaCoO 3 perovskite; Adsorbed oxygen; Lattice oxygen 1. Introduction Perovskite type oxide was found comparable to Pt/Al 2 O 3 [1,2] as an effective catalyst in catalytic oxidations, including total oxidation of hydrocarbons. Perovskite can be used as a gas sensor and in dry cell electrode materials for high tempera- ture solid oxide fuel cells [3,4]. The most important contribution to the high activity of mixed oxides such as the perovskite type oxide, represented by ABO 3 (A: the large ion in the dodecahedral hole and B: the transition metal ion), is distortion in the individ- ual BO 6 octahedra [5,6]. The transition metal B in the perovskite can be particularly active in oxidation catalysis if it can fluctuate between two stable oxidation states [8] to balance electrically: (1) the insertion of O 2 - ion into a lattice from gas phase O 2 , and (2) the formation of oxygen radicals. Two types of oxygen are considered to involve in oxidation reaction, adsorbed (or surface) oxygen () and lattice oxygen () [7]. The adsorbed oxygen () is oxygen on the catalytic surface. It is accommodated in the O 2 - vacancies formed by partial substitution of A-site cations with ∗ Corresponding author. Tel.: +66 2 562 5555x2167; fax: +66 2 579 3955. E-mail address: fsciarw@ku.ac.th (A. Worayingyong). lower valence ions or by vacancies of B-site cations, and involves diffusion of O 2 - ions through the lattice with the formation of neighbouring high valence metal ions [7]. Catalytically active elements (B-site cations) in the perovskite can also be substi- tuted by other atoms to generate oxygen vacancies [8]. Oxygen adsorption from the gas phase and further incorporation of oxy- gen atoms into a lattice, usually leads to three charged oxygen species, namely O 2 - ,O - and O 2- , depending on vacant sites [8]. The adsorbed oxygen () is believed to be more active and reacts with hydrocarbons at lower temperature than the lattice oxygen () [7,9]. During a catalytic reaction, a perovskite often exists with non-stoichiometric composition, including typically the surface oxygen vacancy which could form active oxygen species by adsorbing oxygen (adsorbed oxygen) from gas phase capable for oxidation reaction [5,7]. Metal oxide surfaces have been studied by characterizing hydroxyl (–OH) groups with infrared spectroscopy [10]. X-ray photoemission spectroscopy has also been used to assess the sur- face properties of metal oxides [11] in both hydroxyl and oxide forms. Adsorbed oxygen () and lattice oxygen () equilibrium could be changed by altering metal A/B ratio in the perovskite lattice [7]. 0927-7757/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2008.01.042