TY - JOUR

T1 - Low-Temperature Propylene Epoxidation Activity of CuO-CeO2Catalyst with CO + O2

T2 - Role of Metal-Support Interaction on the Reducibility and Catalytic Property of CuOxSpecies

AU - Baidya, Tinku

AU - Mazumder, Tanmoy

AU - Koltunov, Konstantin Yu

AU - Likhar, Pravin R.

AU - Clark, Adam H.

AU - Tiwari, Khushubo

AU - Sobolev, Vladimir I.

AU - Payra, Soumitra

AU - Murayama, Toru

AU - Lin, Mingyue

AU - Bera, Parthasarathi

AU - Roy, Sounak

AU - Biswas, Krishanu

AU - Safonova, Olga

AU - Srinivasa Rao, Bolla

AU - Haruta, Masatake

N1 - Publisher Copyright: Copyright © 2020 American Chemical Society. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/7/2

Y1 - 2020/7/2

N2 - Epoxidation of propylene into propylene oxide (PO) in the gas phase is a highly challenging reaction. Cu-based catalysts have been active for this reaction, but the state of Cu as an active species is still debatable. In this paper, we report the propylene epoxidation activity of solution combustion synthesized Cu/CeO2 catalysts with the CO + O2 mixture at low temperatures (50-100 °C) peaking at80 °C. The highest PO yield was obtained with 20-25 Cu loading in CeO2. In contrast, the reaction over the catalyst containing nonreducible support such as Cu/SiO2 occurred above 170 °C. Detailed structural characterization indicated two types of Cu species such as Cu2+ partly (∼3%) dissolved in CeO2 forming a CuxCe1-xO2-δ phase and the remaining amount formed highly dispersed CuO as a separate phase. Thus, the highest activity relates to the optimum presence of CuO along with Ce1-xCuxO2-δ. The reducibility of the Cu species in two phases was significantly shifted toward lower temperatures, indicating strong electronic interaction between the two phases. The substituted Cu2+ was reduced first, and then, the bulk CuO reduction was initiated. In situ spectroscopic studies showed Cu+ formation from Cu2+ over Cu/CeO2 catalysts even at room temperature unlike in CeO2 or CuO + CeO2 physical mixtures, indicating strong electronic interaction between Ce1-xCuxO2-δ and CuO phases on CO adsorption in the Cu/CeO2 catalyst. It is proposed that substituted Cu2+ along with Ce4+ is reduced easily, and then, Ce3+ promotes the reduction of the interfacial CuO phase that might donate active oxygen species for epoxidation reaction.

AB - Epoxidation of propylene into propylene oxide (PO) in the gas phase is a highly challenging reaction. Cu-based catalysts have been active for this reaction, but the state of Cu as an active species is still debatable. In this paper, we report the propylene epoxidation activity of solution combustion synthesized Cu/CeO2 catalysts with the CO + O2 mixture at low temperatures (50-100 °C) peaking at80 °C. The highest PO yield was obtained with 20-25 Cu loading in CeO2. In contrast, the reaction over the catalyst containing nonreducible support such as Cu/SiO2 occurred above 170 °C. Detailed structural characterization indicated two types of Cu species such as Cu2+ partly (∼3%) dissolved in CeO2 forming a CuxCe1-xO2-δ phase and the remaining amount formed highly dispersed CuO as a separate phase. Thus, the highest activity relates to the optimum presence of CuO along with Ce1-xCuxO2-δ. The reducibility of the Cu species in two phases was significantly shifted toward lower temperatures, indicating strong electronic interaction between the two phases. The substituted Cu2+ was reduced first, and then, the bulk CuO reduction was initiated. In situ spectroscopic studies showed Cu+ formation from Cu2+ over Cu/CeO2 catalysts even at room temperature unlike in CeO2 or CuO + CeO2 physical mixtures, indicating strong electronic interaction between Ce1-xCuxO2-δ and CuO phases on CO adsorption in the Cu/CeO2 catalyst. It is proposed that substituted Cu2+ along with Ce4+ is reduced easily, and then, Ce3+ promotes the reduction of the interfacial CuO phase that might donate active oxygen species for epoxidation reaction.

KW - GAS-PHASE EPOXIDATION

KW - SMALL GOLD ENSEMBLES

KW - MOLECULAR-OXYGEN

KW - X-RAY

KW - EFFICIENT EPOXIDATION

KW - PROPENE EPOXIDATION

KW - DRIFTS-MS

KW - H-2

KW - O-2

KW - CU

UR - http://www.scopus.com/inward/record.url?scp=85089935305&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.0c00777

DO - 10.1021/acs.jpcc.0c00777

M3 - Article

AN - SCOPUS:85089935305

VL - 124

SP - 14131

EP - 14146

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 26

ER -