Solid-state reaction examination of copper oxide impregnated on pure and La-modified gamma alumina

Abstract

Transition metal oxides dispersed in support oxides have been studied as catalysts for various chemical processes and the removal of environmental pollution. Recently, copper-exchanged zeolites including ZSM-5 have been extensively studied for high potential use as exhaust de-NOx catalysts in automobile engines and factory generator systems [1]. However, the aluminosilicates decompose under thermally hard conditions above 900 °C and following solid-state reactions lead to a large degredation of catalytic activity to remove NOx species. The study of the thermal behaviour and stability of catalytic compositions gives important information for the materials design of new catalysts and the improvement of their thermal durability. Copper oxide impregnated on gamma alumina (7-A1203) has been traditionally examined for oxidation reactions at low temperatures, however, the thermal behaviour at temperatures above 900 °C has rarely been reported. Highly dispersed copper on an alumina support is considered as a potential alternative material for a de-NOx catalyst if its stability can be improved at elevated temperatures. In this letter, we describe the solid-state reaction of highly dispersed copper on pure and La-modified y-A1203. The difference in thermal behaviour of copper oxide between pure and La-modified y-A1203 support and the phase evolution of these systems should be emphasized for the purpose of proposing basic data to develop improved catalysts. La-modified y-A1203 powders with 0 to 10 mol % LaOl.s were prepared by an impregnation procedure, as reported in a previous paper [2]. Powdered alumina with surface area of 100 m2/g was impregnated using an aqueous solution of lanthanum nitrate, and then dried at 110 °C for 10 h and heated at 600 °C for 3 h in air. The impregnation of 5 to 20 mol % Cu to alumina supports was performed by aqueous copper nitrate, and then dried at 110 °C for 10 h and heated at 500 °C for 3 h in air. The samples were heated at temperatures of 800 °C to 1100 °C for 3 h in air. The evolution phases were examined by an X-ray diffraction (XRD) technique. Here we described the case of catalysts having 10 mol % Cu which are supported by pure and 10 mol% Laadded y-Al203 in order to examine the typical effect of La-modification on an alumina support. Fig. 1 shows the XRD patterns of 10mol% Cu-impregnated pure y-A1203 followed by heat treatment temperatures of 800 to 1000 °C for 3 h in air. Pure y-type alumina transforms to 0-type at the temperature range of 800 °C to 1000 °C and changes to 0:-type above 1050 °C. However, the data in Fig. 1 indicate that Cu-impregnated 7-A1203 transforms not to 0-type but to y-type modified with Cu at a temperature range of 800 °C to 900 °C. The characteristics of this Cu-modified y-phase were shown by diffraction peaks at 0.268 and 0.196 nm (20 = 33.4 ° and 46.3 ° in Fig. 1) in addition to the usual y-type pattern [3]. The data are believed to characterize the