Influence of surface composition on hydrogen peroxide decomposition catalyzed by Co(II) aminopyridine-supported compounds on amorphous silica gel.
Cobalt compounds supported on 2-, 3-, and 4-aminopyridine-modified silica surfaces, named Sil2Co, Sil3Co, and Sil4Co, respectively, were used to catalyze the decomposition of hydrogen peroxide on ethanolic solutions at 293, 298, and 303 K. The calculated k values (x10(-4) s(-1)) for Sil2Co, Sil3Co, and Sil4Co are 0.65, 1.24, and 4.78 (293 K); 1.23, 1.87, and 6.33 (298 K); and 1.80, 2.80, and 10.30 (303 K), respectively. All obtained results evidence that such decomposition is a first-order reaction. Zinc-, nickel-, and copper-supported compounds were also tested, but exhibited a very low catalytic activity. By using the k values at 298 and 303 K, and employing the equation ln (k1/k2) = E(a)/R(1/T2-1/T1), the activation energy values for the considered reaction were Sil2Co = 57.20, Sil3Co = 60.60, and Sil4Co = 73.10 kJ mol(-1), respectively. The low values calculated for E(a) are in agreement with a free-radical mechanism.
de Farias
Robson F
RF
Departamento de Química, Universidade Federal de Roraima, C.P. 167, Boa Vista, Roraima, 69301-970, Brazil. robdefarias@bol.com.br
Gonçalves
Afonso S
AS
Airoldi
Claudio
C