Roles of CoAl2O4, Co3O4, and Alumina for Selective Catalytic Reduction of NO with Ethene in Excess Oxygen.

Abstract

The catalytic activities of pure CoAl2O4, Co3O4, physical mixture of CoAl2O4 and Al2O3, and Co3O4 free Co/Al2O3 for the reduction of NO with ethene in excess oxygen, the oxidation of NO, and the oxidation of ethene were investigated to elucidate the activities of CoAl2O4, Co3O4 and Al2O3. Pure CoAl2O4 was more active than Al2O3 for oxidation of NO, the initiation step of the selective reduction of NO over Co/Al2O3, but was less active than Co3O4 for oxidation of ethene. Well-mixed CoAl2O4-Al2O3 catalyst calcined at 800°C had higher activity for selective catalytic reduction of NO with ethene in excess oxygen than catalyst calcined at 500°C as well as roughly-mixed CoAl2O4-Al2O3 catalyst. The high activity of CoAl2O4-Al2O3 catalyst depends on the synergy of CoAl2O4 and Al2O3 particles at their interfaces. Selective removal of Co3O4 from cobalt-loaded alumina, Co3O4-free Co/Al2O3, enhanced the activity for selective catalytic reduction of NO with ethene in excess oxygen, indicating that Co3O4 inhibited the reaction, and that the residual CoAl2O4-like species was catalytically active. High activity of Co/Al2O3 calcined at 800°C for the selective reduction of NO with ethene in excess oxygen is due to the fomlation of CoAl2O4 on the Surface layer of γ-Al2O3.