Janvit Teržan (Author), Matej Huš (Author), Iztok Arčon (Author), Blaž Likozar (Author), Petar Djinović (Author)

Abstract

This research focuses on epoxidation of propylene over pristine, Na, Ca and Cs modified CuOx/SiO2 catalysts using O2. The selectivity of the reaction is analyzed using a combination of catalytic tests, in-situ XAS and DFT calculations. The initially present subnanometer CuO clusters are present in all catalysts which re-disperse/flatten during reaction. During catalytic reaction, the Cu1+ becomes the predominant oxidation state. There is no correlation between propylene oxide (PO) selectivity and copper oxidation state. DFT analysis of the propylene reaction pathway revealed that Na, Cs, and Ca addition decreases the bonding strength of propylene to CuO and decreases the O2 activation barrier, while simultaneously increase the exothermicity of O2 dissociation. The Na induced Cu-O bond modification decreases the activation barrier from 0.87 to 0.71 eV for the oxametallacycle (OMC) ring closure (first step in the reaction pathway favoring selectivity towards PO) compared to pristine 5Cu catalyst. At the same time, we observed an increase (from 0.45 to 0.72 eV) of the barrier for the abstraction of allylic hydrogen. The opposite effect is achieved by Ca addition: the activation barrier for OMC ring closure increases to 1.08 eV and that for allylic hydrogen stripping decreases to 0.16 eV.

Keywords

alkali modification;propylene epoxidation;reaction mechanism;copper oxide;activation barrier;

Data

Language: English
Year of publishing:
Typology: 1.01 - Original Scientific Article
Organization: UNG - University of Nova Gorica
UDC: 54
COBISS: 18333187 Link will open in a new window
ISSN: 0169-4332
Views: 2111
Downloads: 0
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Other data

URN: URN:SI:UNG
Type (COBISS): Not categorized
Pages: str. 1-9
Issue: ǂVol. ǂ528
Chronology: 2020
DOI: 10.1016/j.apsusc.2020.146854
ID: 11798173