A new catalyst based on coprecipitated mixtures or solid solutions of alkaline earth oxides and rare earth oxides, such as mixtures or solid solutions of magnesium oxide and cerium oxide, Mg.sub.5 CeO.sub.x, or magnesium oxide and yttrium oxide, Mg.sub.5 YO.sub.x, which catalyze aldol condensation reactions leading to the selective formation of branched C.sub.4 alcohols. The catalysts may also contain a Group IB metallic component and further an alkali dopant. Preferably, Cu in concentrations at or lower than 30 wt % and K in concentrations at or lower than 3 wt % will be used. The catalyst affords the advantage of being run at pressures lower than those required by prior art catalysts and are more active and selective to methanol and isobutanol.