Abstract
Although ruthenium is a common promoter for cobalt-based Fischer-Tropsch synthesis (FTS) catalysts, the origin of Ru promotion and promoter concentration effects remains controversial. To gain a fundamental understanding of the Ru promotion effects, we herein performed an in situ spectroscopic study by X-ray absorption spectroscopy (XAS), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS)-Auger of working Co/TiO2 catalysts (ca. 12 wt % Co, pure anatase TiO2 phase) promoted with different amounts of Ru (0.1-1.2 wt %). At typical FTS conditions (220 °C, 20 bar, H2/CO = 2), the activity in terms of both metal-time-yield (MTY) and initial turnover frequency (TOF) was maximized for the catalysts promoted with 0.1-0.2 wt % Ru, for which most of the Ru was alloyed with Co in bimetallic nanoparticles. The analysis of Auger electrons evidenced that the lower (apparent) TOF of accessible Co0 sites in the absence of Ru and at Ru concentrations beyond 0.2 wt % is bridged to the development, under reaction conditions, of FTS-inactive cobalt carbide (CoCx) and cobalt oxide (CoOx) patches, respectively, at the outermost surface of cobalt crystallites.
| Original language | English |
|---|---|
| Pages (from-to) | 6042-6057 |
| Number of pages | 16 |
| Journal | ACS Catalysis |
| Volume | 10 |
| Issue number | 11 |
| DOIs | |
| State | Published - Jun 5 2020 |
| Externally published | Yes |
Funding
Financial support by the MINECO of Spain through the Severo Ochoa (SEV2016-0683) and RTI2018-102161 projects is gratefully acknowledged. The authors are thankful to the Microscopy Service of the Universitat Politècnica de València for its assistance in microscopy characterization. XAS experiments at ambient pressure were performed on beamline BM23 at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. We are grateful to Debora Motta Meira at the ESRF for providing assistance in using beamline BM23. Thanks are also due to ALBA synchrotron for allocating beamtime (XAS experiments at higher pressure) and CLÆSS beamline staff for their technical support during the experiment. F.B. (Science without Borders—Process no. 13705/13-0) and C.W.L. (Science without Borders—Process no. 13191/13-6) thank CAPES for a predoctoral fellowship. A.C.F. and E.A.S. acknowledge support to Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award #DE-SC0012573.
| Funders | Funder number |
|---|---|
| U.S. Department of Energy | |
| Office of Science | |
| Basic Energy Sciences | -SC0012573 |
| Basic Energy Sciences | |
| Coordenação de Aperfeiçoamento de Pessoal de Nível Superior | |
| Ministerio de Economía y Competitividad | 13705/13-0, SEV2016-0683, RTI2018-102161, 13191/13-6 |
| Ministerio de Economía y Competitividad |
Keywords
- cobalt catalyst
- Fischer-Tropsch synthesis
- in situ XAS, FTIR, and XPS-Auger spectroscopy
- ruthenium promotion
- TiOsupport