Direct Propylene Epoxidation with Molecular Oxygen over Cobalt-Containing Zeolites

Abstract

Direct propylene epoxidation with molecular oxygen is a dream reaction with 100% atom economy, but aerobic epoxidation is challenging because of the undesired over-oxidation and isomerization of epoxide products. Herein, we report the construction of uniform cobalt ions confined in faujasite zeolite, namely, Co@Y, which exhibits unprecedented catalytic performance in the aerobic epoxidation of propylene. Propylene conversion of 24.6% is achieved at propylene oxide selectivity of 57% at 773 K, giving a state-of-the-art propylene oxide production rate of 4.7 mmol/gcat/h. The catalytic performance of Co@Y is very stable, and no activity loss can be observed for over 200 h. Spectroscopic analyses reveal the details of molecular oxygen activation on isolated cobalt ions, followed by interaction with propylene to produce epoxide, in which the Co2+–Coδ+–Co2+ (2 < δ < 3) redox cycle is involved. The reaction pathway of propylene oxide and byproduct acrolein formation from propylene epoxidation is investigated by density functional theory calculations, and the unique catalytic performance of Co@Y is interpreted. This work presents an explicit example of constructing specific transition-metal ions within the zeolite matrix toward selective catalytic oxidations.

Nitrogen reduction reaction energy and pathways in metal-zeolites: deep learning and explainable machine learning with local acidity and hydrogen bonding features

“…Isolated metal species could be formed in the zeolites in experiment, which are confined within the zeolite micropores or cages. A lot of metal-zeolites have been synthesized and applied in many fields, such as Cu-CHA for the selective catalytic reduction of nitrogen oxides with ammonia, 70 Co-FAU for propylene epoxidation with O 2 , 71 Ni-CHA for the selective hydrogenation of acetylene to ethylene, 72 and Rh-MFI for tandem hydrogenation of nitroarenes. 73 Our study offers a promising strategy for designing efficient metal-zeolite catalysts for nitrogen reduction reactions, which may provide useful guidance to experimentalists for further validation.…”

Stable and Uniform Extraframework Cations in Faujasite Zeolites

“…Herein, some examples of XAS analyses on TMI@zeolites are shown for reference. The oxidation states of Co, Ni, Cu, Rh, and Pt in TMI@FAU zeolites are close to +2 (±0.5, Table ) from X-ray absorption near edge structure (XANES) analyses, − ,, and TMIs with higher or lower oxidation states are difficult to synthesis. This originates from the in situ synthesis route and the self-assembly mechanism of zeolite formation.…”

“…(b) Location of cobalt sites in faujasite from NPD Rietveld refinement. Adapted with permission from ref . Copyright 2022 American Chemical Society.…”

“…(c) The Fourier transform (FT) of k 2 -weighted EXAFS spectra at the K-edge of Co foil, CoO, Co 2 O 3 , and Co@FAU. Adapted with permission from ref . Copyright 2022 American Chemical Society.…”

Research on alkali metal-modified Pd catalyst for oxygen removal from propylene

“…Propylene oxide (PO) is an important petrochemical product with a great market in the chemical industry. Hydrogen-peroxide-to-propylene-oxide technology (HPPO) for the production of propylene oxide has great advantages in environmental protection, which has attracted great attention in recent years (Climent et al, 2011;Lin et al, 2016;Li et al, 2022). The tail gas of the HPPO process contains large amount of oxygen produced by hydrogen peroxide decomposition, which makes the tail gas too dangerous to be separated and recycled (Movileanu et al, 2012;Razus et al, 2009;Razus et al, 2007).…”