Selective synthesis of isobutanol by means of the Guerbet reaction - Part 3: Methanol/n-propanol condensation by using bifunctional catalytic systems based on nickel, rhodium and ruthenium species with basic components

The synthesis of isobutanol ((BuOH)-Bu-i) from methanol/n-propanol (MeOH/PrOH) mixtures has been studied by the Guerbet reaction in the presence of either supported or homogeneous nickel-based/sodium methoxide (MeONa) catalytic systems. The catalysts performances were studied as a function of reaction parameters, such as pre-activation or not of the nickel component, temperature, MeONa/Ni molar ratio, gaseous atmosphere (H-2 or N-2) and the relative amount of the metal in the reacting alcohols mixture. In particular, PrOH conversions to (BuOH)-Bu-i up to 75% were obtained when Ni/kieselguhr//MeONa system was employed. This system appeared more active than Ni/alumina//MeONa. Also homogeneous complexes of nickel such as nickel acetate tetrahydrate and nickel dichloro bis triisopropylphosphine, when combined with MeONa, displayed significant catalytic activity with turnover numbers (TN) up to about 66 mol of (BuOH)-Bu-i/mol of Ni x h. In all cases the selectivity of the process to (BuOH)-Bu-i was substantially complete. Also supported ruthenium and rhodium-based/MeONa catalytic systems were investigated. The results obtained indicated that all the investigated catalysts, when combined with MeONa, resulted active in the synthesis of (BuOH)-Bu-i. The catalytic performances were improved when the metal component was employed without any pre-activation step, very low amount of metal component being sufficient to assure high productivity (turnover values up to about 150 mol of (BuOH)-Bu-i/mol of Ru x h). (C) 2003 Elsevier B.V. All rights reserved.