(377g) Rational Intermetallic Compounds Design for Selective Hydrogenation of Cinnamaldehyde

The catalytic selective hydrogenation of unsaturated aldehydes is a vital reaction to produce both unsaturated alcohols and saturated aldehydes that serve as building blocks for the chemical industry. Intermetallic compounds (IMCs), especially TM+Ga IMCs have shown unique surface chemistry that may be appropriate for selective hydrogenation reactions, e.g., unsaturated aldehydes and nitro compounds to unsaturated alcohols and amine compounds. However, a systematic understanding of IMC surface chemistry in low temperature hydrogenation reactions is still lacking. Selective hydrogenation of cinnamaldehyde over well-defined TM+Ga IMCs (phase pure bulk and bulk-like surface termination) was investigated to understand surface reaction mechanisms and energetics and to isolate ideal surface chemistry to achieve the selective hydrogenation of C=O bonds.

Results illustrate that TM rich IMCs present TM-like surface chemistry, which promotes the unselective hydrogenation of C=C bonds. However, when p-element-rich compositions are employed, surface chemistry shifts to limit C=C hydrogenation and promote C=O hydrogenation. Studies of IMC gallide surface chemistry as a function of TM element selection indicated catalyst formulations that utilize earlier TMs exhibit more aggressive surface chemistry that is not ideal for selective hydrogenation. Correlating surface chemistry with reaction step kinetics also illustrated that new BEP correlations that deviate from pure-metal-derived BEP correlations could be accessed and correlated with d-p-state hybridization within the IMC. Studies of the nature of the reaction site indicated that strong electronic effects dictated IMC surface chemistry and that both TM and p-elements played direct roles in the surface chemistry at mixed composition reaction sites.