Intermetallic nanoparticles are promising catalysts in hydrogenation and fuel cell technologies. Much is known about the ability of intermetallic nanoparticles to selectively reduce nitro, alkyne, alcohol, or halide functional groups; less is known about their selectivity toward aniline vs. azo or azoxy condensation products that result from reduction of a nitro group alone. Because azo(xy) arenes bear promise as dyes, chemical stabilizers, and building blocks to functional materials but can be difficult to isolate, developing high surface area, nanoparticle catalysts that display azo(xy) selectivity is desirable. To address this question, we studied a family of nanocrystalline group 10 metal (Pd, Pt)- and group 14 metal (Ge, Sn, Pb)-containing intermetallics—Pd2Ge, Pd2Sn, Pd3Sn2, Pd3Pb, and PtSn—in the catalytic reduction of nitroarenes. In contrast to monometallic Au, Pt, and Pd nanoparticles, and “random” PdxSn1-x nanoalloys, which are selective for aniline, atomically precise intermetallic nanoparticles of Pd2Ge, Pd2Sn, Pd3Sn2, and PtSn prefer an indirect condensation pathway and have a high selectivity for the azo(xy) products. The only exception is Pd3Pb, the most active among the intermetallic nanoparticles studied here, which is instead selective for aniline. Employing a novel application of Molecular Dynamics—based on machine learned potentials within a DeePMD framework—to heterogeneous catalysis, we are able to identify key reaction species on the different types of catalysts employed, furthering our understanding of the unique selectivity of these materials. By demonstrating how intermetallic nanoparticles can be as active yet more selective than other more traditional catalysts, this work provides new physical insight and opens new opportunities in the use of these materials in other important chemical transformations and applications.

Unveiling the Azo(xy) vs. aniline selectivity in nitroarene reduction with 10–14 intermetallic nanocatalysts

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.