Efficient Heterogeneous Hydroformylation over Zeolite-Encaged Isolated Rhodium Ions

Stable and Uniform Extraframework Cations in Faujasite Zeolites

“…For example, two IR bands at 2105 and 2030 cm −1 are observed on Rh@FAU, ascribed to the symmetric and asymmetric stretching modes of Rh(CO) 2 species while the presence of linear Rh-CO and bridged-CO species can be excluded, demonstrating well-isolated Rh sites in Rh@FAU. 15 In contrast, strong bands at 2060−2070 cm −1 ascribed to linear-absorbed CO on Rh ions as well as weak bands at ∼2110 and ∼2040 cm −1 associated with Rh(CO) 2 species are present on Rh/FAU and Rh-FAU, implying the presence of multiple Rh sites in these samples. In general, FTIR spectroscopy with probe molecules offers a convenient approach to identify the dispersion, uniformity, and existing states of TMIs in the zeolite matrix.…”

“…Typically, Ni@FAU and Co@FAU show sharp reduction peaks at >800 K due to the efficient stabilization of Ni and Co species by the zeolite framework. , Cu@FAU shows a single Cu 2+ → Cu + reduction peak centered at ∼443 K, while the further Cu + → Cu 0 reduction at >523 K is not observed (Figure c), indicating efficient stabilization of Cu + by the zeolite framework . For Rh@FAU, a dominant hydrogen reduction peak of Rh ions is observed at ∼443 K, which is significantly higher than the temperature observed for Rh/FAU (Figure d) . For Pt@FAU, a clear hydrogen reduction peak at high temperature of ∼743 K is observed on Pt@FAU (H/Pt = 1.8) while no reduction peak can be observed for Pt/FAU due to the decomposition of PtOx to metallic Pt during the calcination step (Figure e) .…”

“…22 For Rh@FAU, a dominant hydrogen reduction peak of Rh ions is observed at ∼443 K, which is significantly higher than the temperature observed for Rh/FAU (Figure 2d). 15 For Pt@FAU, a clear hydrogen reduction peak at high temperature of ∼743 K is observed on Pt@FAU (H/Pt = 1.8) while no reduction peak can be observed for Pt/FAU due to the decomposition of PtOx to metallic Pt during the calcination step (Figure 2e). 16 Overall, H 2 -TPR profiles provide intuitive information on the stability and uniformity of TMIs in the matrix of zeolites.…”

“…It is possible to distinguish the atomically dispersed TMIs and their location in the matrix of zeolites. 15,16 For example, the exact location of isolated Pt species in Pt@FAU has been successfully interpreted through the Cs-STEM images taken with distinct incidence. Inferred as bright dots, the atomically dispersed Pt species are confirmed to locate at the six-membered ring shared by sodalite cages and supercages of FAU framework, and the presence of metal clusters can be fully excluded (Figure 4).…”

“…Inspired by the success of Ni@CHA, a general ligand-protected hydrothermal strategy is further developed to construct uniform TMIs in the matrix of FAU zeolites, namely, M@FAU (Si/Al = 2.5–3.5). − The mass loadings of Co, Ni, and Cu can reach as high as ∼5% while the loading of noble metal Rh and Pt is generally below 1%. Since M@FAU zeolites are formed from the self-assembly process of zeolite crystal growth, uniform TMIs are efficiently stabilized in the thermodynamically stable states in the matrix of the FAU zeolite.…”