Division/Committee: [CATL] Division of Catalysis Science & Technology

This symposium will showcase recent work being conducted at the intersection of homogeneous and heterogeneous catalysis i.e hybrid catalysts comprising of either two-dimensionally heterogenized or three-dimensionally confined transition metal molecular complexes. Hybrid catalytic systems comprising of heterogenized transition metal complexes have recently been implicated in industrially relevant processes like the selective catalytic reduction of NOx over Cu-SSZ-13 catalysts where NH3-solvated complexes like [Cu(NH3)4]2+ confined within the zeolitic cage serve as the catalytic active sites. Likewise, a computational study on ethylene dimerization over Ni-SSZ-24 catalysts also suggested that ethylene dimerization occurs over mobile, solvated [(C2H4)2-Ni-alkyl]+ molecular complexes within the zeolite cage. Furthermore, H2O-solvated transition metal molecular complexes confined within zeolite cages can also form under certain reaction conditions, as evidenced by recent computational and/or experimental studies (Cu, Pd, and Fe).The referenced literature also suggests that a unique feature of such hybrid catalytic systems is that the solvated transitional metal ions are mobile within the confining environment of the solid support (say zeolite), and the catalytic cycle occurs on these mobile molecular complex sites that can reversibly interconvert among various mono- di- and multi-nuclear molecular complexes to mediate distinct elementary steps during steady-state catalytic turnover. Elsewhere, examples of pre-synthesized hybrid catalytic systems composed of heterogenized molecular catalysts also exist in the literature where hybrid catalysts were used for various catalytic chemistries including nitroarene reduction, ethylene polymerization, fuel reforming, electro-reduction of oxygen, electro-reduction of carbon dioxide, alkene metathesis, water oxidation, etc. Noting literature reported examples of intentional (pre-synthesized) and unintentional (formed in situ during reaction) hybrid catalytic systems, it becomes clear that a more systematic, rational design approach needs to be taken to study the unique interactions and dynamics within such hybrid catalysts to ultimately develop transformative technologies and bridge the knowledge gap between homogeneous-heterogeneous catalysis. Specifically, rationally designed hybrid catalytic systems based on non-toxic, heterogenized transition metal molecular complexes hold promise for sustainable catalysis and green chemistry applications. The catalytic sites in such hybrid catalysts are expected to exhibit enhanced tunability with ligand-field chemistry, which can ultimately yield atomically efficient, dynamic catalytic sites that are more active and/or selective than traditional heterogeneous catalysts and homogeneous catalysts. This symposium aims to highlight some of the challenges of studying hybrid systems and provide state-of-the-art insights into the most suitable experimental and computational techniques to circumvent some of those challenges.

Chad Palumbo

National Renewable Energy Laboratory

Appearances