284714 Hydrogenolysis of Polyols and Cyclic Ethers On ReOx-Promoted Pt and Rh Catalysts
Selective hydrogenolysis of biomass-derived compounds is one fundamental strategy of producing fuels and value-added chemicals. One class of chemicals of interest are α,ω-diols, which could be useful in polymer applications. Strategies to producing these α,ω-diols include selective hydrogenolysis of polyols, such as glycerol and cyclic ethers, in which the ether ring is opened to form linear diols. In order to achieve high selectivity, the hydrogenolysis of polyols must only activate C-O bonds on secondary carbons (to preserve the alcohol groups at the α and ω positions). Thus, acid-catalyzed dehydration reactions, followed by hydrogenation, should yield the desired saturated diol products. Similarly, during conversion of cyclic ethers, if the ether is substituted with a hydroxymethyl group at a carbon adjacent to the ether oxygen, acid-catalyzed ring opening would preferentially cleave the C-O bond of the substituted carbon, placing hydroxyl groups at the desired α and ω positions. Recent studies have demonstrated ReOx and other promoters can increase the activity and selectivity of supported Rh and Pt catalysts for these reactions. Characterization has demonstrated that the oxide promoters are partially reduced in the presence of the Pt-group metal and it is known that in the presence of water, these partially oxidized clusters are likely to hydroxylate. Furthermore, NH3 TPD studies have shown strongly bound NH3species, indicative of Brønsted acid sites. These studies have suggested model systems which can be used to demonstrate the acidity of such systems.
In this study, we set out to examine the impacts of 1) alloy composition (altering the fully reduced and partially oxidized metal), 2) particle size, 3) site and structure of the alloy on the nanoparticle. Furthermore, we have demonstrated that ring-opening hydrogenolysis can proceed through an acid catalyzed route on these model surfaces, and that the formation energy of the carbenium ion intermediates correlates to the reactivity of a range of reactants.