A study of Cu/ZnO/Al2O3 methanol catalysts prepared by flame combustion synthesis

The flame combustion synthesis of Cu/ZnO/Al2O3 catalysts for the synthesis of methanol from CO, CO2, and H-2 is investigated. The oxides are generated in a premixed flame from the acetylacetonate vapours of Cu, Zn, and Al mixed with the fuel and air prior to combustion. The flame-generated powder is examined by X-ray powder diffraction, determination of the specific surface area by the BET method, determination of the copper dispersion in the reduced catalyst by a novel N2O method, transmission electron microscopy, and testing of the catalytic properties in a catalytic microreactor. A low peak temperature and quench cooling of the flame tend to increase the dispersion of the phases and the specific surface area of the particles. Properties of both the ternary composition, the three binary compositions, and the pure oxides are discussed. The calculation of simultaneous phase and chemical equilibrium is used in the assessment of the phase composition of the particles. The specific surface area varies from 100 m(2)/g or a little below for samples without Al to several hundred m(2)/g for the respective compositions of pure Al2O3 and ZnAl2O4, Copper dispersion after reduction varies from 1.8 to 14.1%. A ternary catalyst with the composition of Cu:Zn:Al = 45:45: 10 has the highest catalytic activity of all samples tested. This catalyst is also very selective and stable toward thermal deactivation. The role of the individual catalyst components in the optimal catalyst is discussed. (C) 2003 Elsevier Inc. All rights reserved.