Ultra‐Low Loading Pt/CeO₂ Catalysts: Ceria Facet Effect Affords Improved Pairwise Selectivity for Parahydrogen Enhanced NMR Spectroscopy

Abstract

Oxide supports with well‐defined shapes enable investigations on the effects of surface structure on metal–support interactions and correlations to catalytic activity and selectivity. Here, a modified atomic layer deposition technique was developed to achieve ultra‐low loadings (8–16 ppm) of Pt on shaped ceria nanocrystals. Using octahedra and cubes, which expose exclusively (111) and (100) surfaces, respectively, the effect of CeO2 surface facet on Pt‐CeO2 interactions under reducing conditions was revealed. Strong electronic interactions result in electron‐deficient Pt species on CeO2 (111) after reduction, which increased the stability of the atomically dispersed Pt. This afforded significantly higher NMR signal enhancement in parahydrogen‐induced polarization experiments compared with the electron‐rich platinum on CeO2 (100), and a factor of two higher pairwise selectivity (6.1 %) in the hydrogenation of propene than any previously reported monometallic heterogeneous Pt catalyst.

Heterogeneous 1H and 13C Parahydrogen‐Induced Polarization of Acetate and Pyruvate Esters

“…Moreover, HET‐PHIP catalysts can be potentially recycled [63] . Heterogeneous catalysts provide somewhat lower polarization levels compared to homogeneous catalysts due to lower contribution of pairwise hydrogen addition route to the overall hydrogenation mechanism [64–66] . Nevertheless, the HET‐PHIP catalyst development remains a hot area of research with the key goals to expand the scope of amenable substrates [67–69] and improve polarization yields [66,70,71] .…”

“…Heterogeneous catalysts provide somewhat lower polarization levels compared to homogeneous catalysts due to lower contribution of pairwise hydrogen addition route to the overall hydrogenation mechanism [64–66] . Nevertheless, the HET‐PHIP catalyst development remains a hot area of research with the key goals to expand the scope of amenable substrates [67–69] and improve polarization yields [66,70,71] . In PHIP‐SAH studies, heterogeneous Rh/TiO 2 catalyst allowed obtaining 13 C polarization ( P 13C ) of 0.035 % for ethyl [1‐ 13 C]acetate in organic solvents [72] and P 13C =0.011 % in aqueous media [61] .…”

Mesoporous titanium niobium nitrides supported Pt nanoparticles for highly selective and sensitive formaldehyde sensing

“…The increase in selectivity of the Pt/Ti 0.75 Nb 0.25 N sensor may be due to the change of adsorption and electrochemical activity of the catalyst for different gases. 52 By controlling the composition of support materials, a more complex surface electronic structure can be constructed and the synergistic effect between the catalyst and support materials can be increased. 53 This changes the gas adsorption at the three-phase reaction interface and the catalytic activity of gas sensing materials for different gases.…”

Heterogeneous Catalysis and Parahydrogen‐Induced Polarization

“…[54] Alternatively, atomically dispersed metal on a solid surface can be obtained by atomic layer deposition of an active metal on an oxide support. For instance, [83] the catalysts with ultra-low loadings (8-16 ppm) of Pt on shaped ceria nanocrystals were recently investigated by PHIP (Figure 6). CeO 2 octahedra and cubes exclusively expose ( 111) and (100) surfaces, respectively, facilitating the studies of the effect of CeO 2 surface facet on the PtÀ CeO 2 interactions under reducing conditions.…”