COPPER ZIRCONIA CATALYSTS FOR THE SYNTHESIS OF METHANOL FROM CARBON-DIOXIDE - INFLUENCE OF PREPARATION VARIABLES ON STRUCTURAL AND CATALYTIC PROPERTIES OF CATALYSTS

The effect of the preparation method on the catalytic behaviour of copper/zirconia catalysts for the synthesis of methanol from carbon dioxide has been investigated. Conventional precipitation, ion exchange and impregnation methods have been used in addition to the methods of deposition precipitation and co-precipitation in the presence of reducing agents. Precipitation reactions at constant pH were found to be an interesting route for the preparation of highly active and selective Cu/ZrO2 catalysts. Efficient catalysts were found to consist of microcrystalline copper particles which are stabilised through interaction with an amorphous zirconia matrix, resulting in a high interfacial area. The determination of the copper surface area by nitrous oxide titration revealed that the methanol synthesis activity did not exhibit a general correlation with the specific copper surface area of the catalysts; such a correlation is found only within families of similarly prepared catalysts. The influence of the residence time on the relative selectivity gamma (CH3OH/CO) was investigated in the temperature range 473 to 533 K at a pressure of 1.7 MPa. The results indicated that methanol and desorbing carbon monoxide are probably formed from carbon dioxide via parallel reaction pathways. The activation energies calculated from these results were E(A) = 47.9 +/- 1.4 kJ mol-1 for the methanol synthesis reaction and E(A) = 93.2 +/- 2.9 kJ mol-1 for carbon monoxide formation.