Coordination and properties of cobalt in the molecular sieves CoAPO-5 and -11

• Published in: Microporous and mesoporous materials Vol. 37; no. 1; pp. 117 - 127
• Main Authors: SPONER, J, CEJKA, J, DEDECEK, J, WICHTERLOVA, B
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.05.2000; Elsevier
• Subjects: AlPO 4; Chemistry; Co ions; CoAPO-11; CoAPO-5; Exact sciences and technology; General and physical chemistry; Ion-exchange; Molecular sieves; Other ion exchangers: preparations and properties; Redox sites; Surface physical chemistry; Co ions; CoAPO-11; CoAPO-5; Redox sites; AlPO 4; Molecular sieves; Water; Diffuse reflection; Cobalt ion; Visible spectrometry; Experimental study; Ultraviolet spectrometry; Molecular sieve; Calcining; Operating conditions; Reflection spectrometry; Near infrared spectrometry; Chemical coordination; Amine; Adsorption; Ligand field; Aluminium phosphate; Modified material
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/S1387-1811(99)00258-9

Diffuse reflectance electronic spectra have been utilized to investigate the local geometry of cobalt centers substituted in the three-dimensional framework of CoAPO-5 and -11 molecular sieves. Structural changes induced by calcination in an oxidative atmosphere, evacuation and hydrogen treatment, as well as by adsorption of amines and water are discussed in terms of the steric conditions of cobalt incorporation in the aluminophosphate matrix. We suggest a template–framework interaction between the framework cobalt centers and neutral amine-type templates as an alternative stabilizing effect in the as-synthesized samples. Spectral changes observed after calcination in oxygen are interpreted as distortion-induced charge transfer effects without oxidation of the divalent cobalt ions. Formation of oxygen vacancies in the close vicinity of the cobalt sites is proposed to explain the adsorption properties of the framework cobalt centers.