(532co) Catalytic Surface Chemistry of Non-Noble Transition Metal Borides in the Selective Hydrogenation of Unsaturated Aldehydes and Nitro Compounds

Selective hydrogenation of unsaturated aldehydes is a classically difficult reaction to control due to the reactivity of C=O and C=C moieties.

Intermetallic compounds (IMC), which are compositionally ordered solid compounds composed of TM and P-block elements, have shown promise in providing new and unique surface chemistry that may be appropriate for catalyzing selective hydrogenation reactions. However, systematic understanding of how IMC catalytic surface chemistry is dictated by IMC composition is still lacking. Using the selective hydrogenation of cinnamaldehyde as a probe reaction, we investigated the catalytic surface chemistry of late 1st-row TM+B IMCs. Using a reactive-support approach, we developed a synthesis method to produce high-surface-area, supported boride nanoparticle catalysts with phase pure bulk compositions. Utilizing a combination of experimental catalyst performance and DFT surface reaction modeling studies, we have developed a systematic understanding of TM boride surface chemistry in the selective hydrogenation of C=O and nitro groups while preserving unsaturated C=C bonds.

Results illustrated that elevated surface oxophilicity of TM borides favored activation and hydrogenation of the C=O bond. On the other hand, catalysts that exhibited significantly elevated oxophilicity could drive C=O and N-O bond cleavage. Studies also indicated that the elevated reactivity of the TM borides could lead to surface composition changes under reaction conditions. The role of these composition changes in producing active and selective reaction sites were understood through focused computational and post-reaction characterization studies. Ultimately, trends in the surface chemistry of TM borides and highly selective catalysts were developed. Lastly, the ability to produce significantly elevated surface oxophilicity can be useful in many other catalytic chemistries where C-O cleavage is required or more strongly bound oxidizing intermediates are needed.