title: Shaped Ceria Nanocrystals Catalyze Efficient and Selective Para-Hydrogen-Enhanced Polarization.
abstract: Intense para-hydrogen-enhanced NMR signals are observed in the hydrogenation of propene and propyne over ceria nanocubes, nano-octahedra, and nanorods. The well-defined ceria shapes, synthesized by a hydrothermal method, expose different crystalline facets with various oxygen vacancy densities, which are known to play a role in hydrogenation and oxidation catalysis. While the catalytic activity of the hydrogenation of propene over ceria is strongly facet-dependent, the pairwise selectivity is low (2.4% at 375 °C), which is consistent with stepwise H atom transfer, and it is the same for all three nanocrystal shapes. Selective semi-hydrogenation of propyne over ceria nanocubes yields hyperpolarized propene with a similar pairwise selectivity of (2.7% at 300 °C), indicating product formation predominantly by a non-pairwise addition. Ceria is also shown to be an efficient pairwise replacement catalyst for propene.
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, FL 32611 (USA).
authors.forename: Evan W
authors.initials: EW
authors.lastname: Zhao
authors.affiliation: Department of Chemical Engineering, University of Florida, Gainesville, FL 32611 (USA).
authors.forename: Haibin
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, FL 32611 (USA).
authors.forename: Ronghui
authors.initials: R
authors.lastname: Zhou
authors.affiliation: Department of Chemical Engineering, University of Florida, Gainesville, FL 32611 (USA). hweaver@che.ufl.edu.
authors.forename: Helena E
authors.initials: HE
authors.lastname: Hagelin-Weaver
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, FL 32611 (USA). bowers@chem.ufl.edu.
authors.forename: Clifford R
authors.initials: CR
authors.lastname: Bowers
keywords: NMR spectroscopy; catalysis; ceria; hydrogenation; nuclear spin hyperpolarization