Mechanistic in situ investigation of heterogeneous hydrogenation over Rh/TiO₂ catalysts: selectivity, pairwise route and catalyst nature

Abstract

Selectivity to the products formation is strongly correlated with the nature of catalyst active centers. Therefore, the selective synthesis of active sites with certain structure is a big challenge in...

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

“…HET‐PHIP‐SAH experiments were performed using Rh/TiO 2 catalysts (0.97 wt.% or 20 wt.% of Rh metal) in liquid phase with methanol‐d 4 or D 2 O as solvents. Rh/TiO 2 catalysts were chosen because they previously demonstrated the highest polarization levels among various monometallic supported metal catalysts [65,77,78] . The following PHIP experiments were carried out: PASADENA [29] (hydrogenation with p‐H 2 at high magnetic field), ALTADENA [79] (hydrogenation with p‐H 2 at Earth's magnetic field with subsequent transfer of the sample to the high field), and MFC [41] (hydrogenation with p‐H 2 at Earth's magnetic field with subsequent transfer of the sample to magnetic shield and then to the high field) for polarization transfer to 13 C nuclei.…”

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

“…The pairwise selectivity of 6.1 % obtained over the Oct‐8ppm catalyst is significantly higher than the 0.3–0.4 % obtained over a conventionally prepared Pt/TiO 2 catalyst run under similar conditions (Supporting Information, Figure S8). Amongst monometallic heterogenous catalysts, only supported Rh, a metal known to give higher pairwise selectivities than Pt, has yielded a similar pairwise selectivity in the hydrogenation of propene [15] …”

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

“…Amongst monometallic heterogenous catalysts, only supported Rh, a metal known to give higher pairwise selectivities than Pt, has yielded a similar pairwise selectivity in the hydrogenation of propene. [15] A lower pairwise selectivity (2.7 %) is observed over the Cub-10ppm catalyst which displayed Pt nanoparticle formation, but this is still significantly higher than that obtained with the conventional Pt/TiO 2 catalyst under the same conditions, and it is comparable to the best supported Pt catalyst in the literature. [14] Furthermore, the reaction rates normalized to the Pt content of the catalysts in this study are several orders of magnitude higher than those of the Pt/TiO 2 catalyst (Figure 3 c), which means that the Pt is utilized very efficiently in these ultra-low loading catalysts.…”