ISOTOPE STUDIES OF THE EFFECT OF ACID SITES ON THE REACTIONS OF C-3 INTERMEDIATES DURING ISOSYNTHESIS OVER ZIRCONIUM DIOXIDE AND MODIFIED ZIRCONIUM DIOXIDE

CO hydrogenation reactions over zirconium dioxide at 425°C and 35 atm proceeds by two chain growth steps to C4 products, CO insertion into aldehydic ZrC bonds, and condensation between methoxide and η3-enolates. Carbon-13-labeled acetone and methanol were co-fed with CO/H2 to study the effect of surface acid and base characteristics on the C3 intermediates and their reactions leading to C4 hydrocarbon products. Studies were conducted over zirconium dioxide, H2SO4 modified zirconium dioxide, 9% Sc2O3ZrO2, 9% Y2O3ZrO2 and 9% Sm2O3ZrO2. Branched C3 intermediates were more likely than linear C3 intermediates to form on acidic catalysts. Lewis acid sites enhanced the condensation reaction involving a reaction between an η3-enolate and a methoxide. The more acidic the catalyst, the greater the percentage of C4 products. However, the most acidic catalysts did not necessarily have the highest branched-to-linear ratios. The importance of enolate stabilization and of the condensation reaction on the isosynthesis reaction are discussed. © 1990.