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Acid–base properties of Cu 1−x Co x Fe 2 O 4 ferrospinels: FTIR investigations

2002; Royal Society of Chemistry; Volume: 4; Issue: 17 Linguagem: Inglês

10.1039/b204226f

1463-9084

Thomas Mathew, Balkrishna B. Tope, N. Raveendran Shiju, S.G. Hegde, Bollapragada S. Rao, Chinnakonda S. Gopinath,

Layered Double Hydroxides Synthesis and Applications

Systematic IR spectroscopic studies were undertaken to investigate the acid–base properties of Cu–Co ferrospinels Cu1−xCoxFe2O4 (x = 0 to 1) employed in phenol methylation to produce 2,6-xylenol. The IR spectra of the ferrospinels reveal that Fe3+ and Co2+ ions are mainly responsible for the various hydroxy groups on the surface. Temperature dependent IR studies of pyridine adsorbed on spinels and on the spinel phase with deliberately added metal oxide exemplify the contribution of the metal ions and their coordination state towards Lewis acidity. IR studies of the spinel surface with adsorbed CO2 and adsorption studies of electron acceptors such as 7,7,8,8-tetracyanoquinodimethane, 2,3,5,6-tetrachloro-1-4-benzoquinone and p-dinitrobenzene were carried out to evaluate the nature of the basic sites and the strength and distribution of the electron donor sites present on the spinel surface. It was found that the acidity (basicity) of the Cu1−xCoxFe2O4 spinel system increases (decreases) from x = 0 to 1. A correlation between acidity, basicity and catalytic performance reveals that an intermediate acid–base character enhances the phenol methylation activity.