Abstract
A Pd-promoted Re/SiO2 catalyst was prepared by sequential impregnation and compared to monometallic Pd/SiO2 and Re/SiO2. All samples were characterized by electron microscopy, H2 and CO chemisorption, H2 temperature-programmed reduction, and in situ X-ray absorption spectroscopy at the Re LIII and Pd K-edges. The samples were also tested in the reduction of propionic acid to 1-propanol and propionaldehyde at 433 K in 0.1-0.2 MPa H2. Whereas monometallic Pd was inactive for carboxylic acid reduction, monometallic Re catalyzed aldehyde formation but only after high-temperature prereduction that produced metallic Re. When Pd was present with Re in a bimetallic catalyst, Pd facilitated the reduction of Re in H2 to ∼+4 oxidation state at modest temperatures, producing an active catalyst for the conversion of propionic acid to 1-propanol. Under the conditions of this study, the orders of reaction in propionic acid and H2 were approximately zero and one, respectively. Transient kinetic analysis of the carboxylic acid reduction to alcohols revealed that at least 50% of the Re in the bimetallic catalyst participated in the catalytic reaction. The Pd is proposed to enhance the catalytic activity of the bimetallic catalyst by spilling over hydrogen that can partially reduce Re and react with surface intermediates.
Original language | English |
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Pages (from-to) | 12353-12366 |
Number of pages | 14 |
Journal | ACS Sustainable Chemistry and Engineering |
Volume | 6 |
Issue number | 9 |
DOIs | |
State | Published - Sep 4 2018 |
Funding
Electron microscopy was performed at the University of Virginia’s Nanomaterials Characterization Facility, and at Oak Ridge National Laboratory’s Center for Nanophase Materials Science. This work was carried out with the support of the Diamond Light Source on proposal number SP13561-1. We thank Diamond Light Source for access to beamline B18 that contributed to the results presented here. Dr. Giannantonio Cibin is also acknowledged for his assistance in the setup of the in situ reactor at Diamond Light Source. This research also used beamline 8-ID of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. *Phone: 1-434-924-6284. E-mail: [email protected]. ORCID Jiahan Xie: 0000-0003-1754-9844 Ian J. Godfrey: 0000-0002-9195-1332 Raymond R. Unocic: 0000-0002-1777-8228 Gopinathan Sankar: 0000-0001-5152-3424 Robert J. Davis: 0000-0002-5859-3457 Funding This material is based upon work supported by the National Science Foundation (NSF) under Award No. EEC-0813570. Notes Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF. The authors declare no competing financial interest. This material is based upon work supported by the National Science Foundation (NSF) under Award No. EEC-0813570.
Keywords
- 1-Propanol
- Carboxylic acid
- Palladium
- Propionaldehyde
- Propionic acid
- Rhenium
- Transient kinetics
- X-ray absorption spectroscopy