Copper-cobalt oxide spinel supported on high-temperature aluminosilicate carriers as catalyst for CO-O2 and CO-NO reactions

A copper-cobalt oxide spinel supported on high-temperature aluminosilicate carriers (90 wt% boehmite (pseudoboehmite)+10 wt% activated bentonite, calcined at T-calcin=800, 1000, 1050 or 1150 degrees C) has been prepared, characterized and tested in CO-O-2 and CO-NO reactions. X-ray diffraction (XRD) has shown the presence of different forms of Al2O3 in the carriers: gamma-Al2O3 for B800; gamma-Al2O3+delta-Al2O3 for the B1000, delta-Al2O3+theta-Al2O3+alpha-Al2O3 for the B1050 and alpha-Al2O3 for the carrier B1150, The carriers have very high mechanical strength. With increasing T-calcin the surface area of carriers changes from 133 to 13 m(2)/g. XRD has shown the presence of a spinel phase for all Cu-Co supported samples. The adsorption capacity of Al2O3 supports towards Cu ions is related to the surface area of carriers and is of essential importance for the Cu and Co loading. The amounts of loaded metals Cu and Co change in an opposite manner with increasing T-calcin. However, the total amount of loaded metals (Cu+Co) is almost constant, The weight ratio Co : Cu increases to almost that of the closer to the stoichiometric value for the CuCo2O4 spinel. It is suggested that the whole amount of Co is engaged in the formation of Cu-Co spinel phase observed by XRD. The catalysts have shown high activity towards both CO-O-2 and NO-CO reactions. The same order of activity of catalysts SB800<SB1000<SB1050<SB1150 has been established for both reactions. The activity of catalysts has been correlated with the amount of (Cu+Co) engaged as a Cu-Co spinel phase which increases in the same order. In the case of CO-NO reaction, the 'onset' temperatures for the CO-O-surf reaction is lower than that for the CO-NO reaction itself. At temperatures above 240 degrees C, the CO-NO reaction is affected by the competition of CO-O-surf reaction. It has been suggested that the low-temperature (below 200 degrees C) mechanism of NO-CO reaction includes formation of (NO . CO)* complexes which is the rate-limiting step. (C) 1998 Elsevier Science B.V. All rights reserved.