The Role of MgAl_2O_4, CaAl_2O_4 Layers in the Catalyst La_(0.8)Sr_(0.2)CoO_3/γ―Al_2O_3

摘要

Supported combustion catalyst La_(0.8)Sr_(0.2)CoO_3/γ― Al_2O_3(LSC/γA)was expected to possess relatively high activity for the oxidation of carbon monoxide and hydrocarbons. But cobalt ions can react with γ―Al_2O_3 at not very higher temperature to form spinel CoAl_2O_4, which deereases the activity of the combustion catalyst. In our previous work, MgAl_2O_4 layer which was covered on the surface of γ―Al_2O_3 could hinder the reaction between cobalt ions and γ―Al_2O_3, but MgAl_2O_4 layer should be thick enough to reach 30wt. %MgO of support due to coarse particles of MgAl_2O_4. In this work, PVA(Poly Vinyl alcohol)was added to the impregnation solution adequately. In such a way, MgAl_2O_4 particles formed on the surface of γ―Al_2O_3 were small. When CaAl_2O_4 layer substituted for MgAl_2O_4, more closed cover was obtained in virtue of fine particles of CaAl_2O_4. The activity examination showed that smaller particles of MgAl_2O_4 or CaAl_2O_4 could be more effective to hinder cobalt ions entering the lattice of γ―Al_2O_3.