Cobalt-alumina sol gels: Effects of heat treatment on structure and catalytic ability

Cobalt-alumina (Co-Al) aerogel catalysts show potential as less expensive, sustainable alternatives to the platinum-group-metal catalysts used in three-way catalytic converters. Effects of heat treatment on the structure of Co-Al xerogels and aerogels and catalytic performance of Co-Al aerogels were investigated. Alumina gels were prepared by epoxide-assisted sol-gel synthesis, impregnated with similar to 3% cobalt, and either processed via rapid supercritical extraction to yield aerogels, or dried under ambient conditions to form xerogels. These materials were calcined at temperatures ranging from 400 degrees C to 1100 degrees C and characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction, thermogravimetric analysis and Brunauer-Emmett-Teller gas adsorption. When the aerogels and xerogels were heated to similar to 500 degrees C, crystalline portions of the alumina support underwent the expected phase transformation from boehmite to gamma-alumina. Aerogels resisted further changes in samples heated to 1100 degrees C, whereas gamma-alumina in the xerogels converted to alpha-alumina by 1100 degrees C. Heat-treated aerogels had high thermal stability, evidenced by their maintaining a surface area of 400 (+/- 30) m(2)/g after significant heating and resisting catalytically inhibiting theta/alpha-alumina phase changes. Color changes observed following heating are consistent with changes in cobalt-containing species within the materials. Preliminary catalytic tests showed that pre-heating Co-Al aerogels to 750 degrees C improves catalytic performance. (C) 2016 Elsevier B.V. All rights reserved.