Enhanced propylene oxide selectivity for gas phase direct propylene epoxidation by lattice expansion of silver atoms on nickel nanoparticles

Abstract

A series of surfactant-free nickel-core and silver-shell (Ni@Ag) nanoparticles encapsulated within the mesopores of SBA-15 were synthesized and tested as catalysts for direct propylene oxidation by molecular oxygen. The influences of temperature, Gas Hour Space Velocity (GHSV) and Ni/Ag ratio on catalytic activity were systematically investigated. Among the prepared samples, Ni1Ag0.4/SBA-15 exhibited the best catalytic performance with selectivity of 70.7% and PO production rate of 4.4 nmol/g/s under 1 bar at 220 o C with GHSV of 192 h-1. High selectivity was attributed to longer Ag-Ag interatomic distance obtained by careful engineering the thickness of Ag shell over preformed Ni nanoparticles. In addition, all prepared new Ni@Ag core-shell catalysts presented excellent stability, which could maintain the conversion and selectivity for at least 10 hours. These results suggest that new designs based on Ag surface atoms tailoring might pave the way to highly efficient and robust Ag catalysts for direct propylene oxidation using molecular oxygen as sole oxidant.

Propylene Epoxidation using Molecular Oxygen over Copper- and Silver-Based Catalysts: A Review

“…Similarly, modification of the Ag–Ag interatomic distances was achieved in core–shell Ag@Ni/SBA-15 catalysts (Figure ), according to an EXAFS analysis by Yu et al Their results indicate that Ni is in the core of the nanoparticles, which are encapsulated by a ∼1 nm thin layer of Ag atoms. With an optimal nickel to silver ratio (Ni 1 Ag 0.4 ), the core–shell catalysts exhibited excellent stability after 10 h of TOS with a PO selectivity of ∼70% at a propylene conversion under 1%.…”

“…Schematic representation of Ni–Ag core–shell catalysts used by Yu et al Reproduced with permission from ref . Copyright 2018, Elsevier.…”

Insight into the Effect of Copper Substitution on the Catalytic Performance of LaCoO3-Based Catalysts for Direct Epoxidation of Propylene with Molecular Oxygen

“…Propylene oxide (PO) is one of the most important raw materials that are essential to produce chemicals such as propylene glycol ethers, propylene glycol, and polyether polyols. , Conventionally, PO has been fabricated by the chlorohydrin (CHPO) and Halcon processes . However, the CHPO process produces numerous pollutants while the latter brings a great amount of coproducts which limits the economic efficiency .…”

“…However, the Ag-based catalysts for propylene epoxidation usually exhibit poor performance as compared to that for ethylene epoxidation. This is because the allylic hydrogen of propylene is easily attacked, resulting in the complete oxidation of propylene . Meanwhile unsupported or supported Cu-based catalysts also demonstrate potentials in catalytic epoxidation of propylene to propylene oxide.…”

“…This is because the allylic hydrogen of propylene is easily attacked, resulting in the complete oxidation of propylene. 2 Meanwhile unsupported or supported Cu-based catalysts also demonstrate potentials in catalytic epoxidation of propylene to propylene oxide. When Cu-based supported on SiO 2 is initially confirmed to be feasible for propylene epoxidation (selectivity of 32.6%, conversion of 0.3%), 19 the researchers proved that the active phase for the reaction is Cu 0 .…”