Expanded lattice ruthenium pyrochlore oxide catalysts I. Liquid-phase oxidations of vicinal diols, primary alcohols, and related substrates with molecular oxygen

Abstract

Ternary ruthenium oxide oxidation catalysts are reported that function directly with molecular oxygen for the conversion of oxygenated hydrocarbon substrates to carboxyl-containing products. The oxide catalysts have an expanded lattice pyrochlore structure with the general composition A 2+ x Ru 2−y( A = Pb, Bi; 0 < x < 1; 0 < y < 0.5). These pyrochlore oxide catalysts possess high surface areas, may be used either as powders for batch autoclave reactors or granules for continuous trickle bed reactors, and operate under O 2 pressure at temperatures of 25 to 95°C in aqueous alkaline solutions. Functional group reactivity of substrates (ketone > 1,2-diol > primary alcohol) over these oxide catalysts closely follows that reported previously when these oxides are used as anodic electrocatalysts suggesting common surface intermediates. Trickle bed reactor operation provides the highest product selectivity: trans-1,2-cyclohexanediol is oxidatively cleaved to adipate in NaOH solutions with 74 to 95% selectivity at contact times of 0.042 to 0.784 hr and temperatures of 26 to 95°C. The bismuth-containing oxides, Bi 2+xRu 2−xO 7−y, show stable catalyst performance under trickle bed reactor operation for over 180 hr. Complete details of these catalytic oxidations are provided along with a discussion of substrate reaction pathways and oxygen activation by these novel expanded lattice ruthenium pyrochlore oxide catalysts.