Mossbauer and XPS Characterization of Fe-Based Fischer-Tropsch Catalysts
EMSL Project ID
23991
Abstract
This proposal seeks to characterize fresh and used Fe-based Fischer-Tropsch synthesis (FTS) catalysts prepared at the Research Triangle Institute (RTI) using combined Mossbauer and X-ray photoelectron spectroscopy (XPS) at the Pacific Northwest National Laboratory (PNNL) - Environmental Molecular Sciences Laboratory (EMSL) facility. The overall objective of the work is to evaluate phase changes occurring on the catalyst surface during use and to relate these changes with catalyst activity and extent of deactivation. Fischer-Tropsch synthesis (FTS) is a well known catalytic process for converting syngas (H2 + CO) derived from non-petroleum feed stocks such as coal, biomass, and natural gas to a wide variety of clean hydrocarbons, particularly diesel and premium waxes. For the past several years, RTI has been working on developing Fe-based FTS catalysts. Numerous catalysts have been prepared by spray drying and tested in fixed-bed and slurry reactors over a range of temperature, pressure and syngas compositions. One superior catalyst has also been evaluated in a SBCR pilot-plant at Rentech. Since Fe carbide is the primary active phase for Fe-based FTS catalysts, they are typically activated in situ using CO or syngas. Once active, the FTS reaction results in less reducing and carbiding conditions due to the formation of CO2 and steam. To maintain high activity and minimize catalyst deactivation, run conditions need to be chosen carefully to balance carbiding with reoxidation and prevent over carburization. Understanding these characteristics of the catalyst will be very helpful to derive structure-activity correlation, to select the best activation and operating conditions, and to further improve the catalytic activity and selectivity to the desired hydrocarbon.
The proposed activity involves the characterization of a few (8-10) selected Fe-based FTS catalysts developed at RTI in the fresh form, after activation under syngas, and used catalyst after the FTS reaction using both Mossbauer and XPS. In order to confirm the nature of active sites more precisely, the measurements will also be performed under the same conditions over a few reference samples such as Fe2O3, Fe3O4, Fe carbides, etc as needed. Thus, the Mossbauer and XPS measurement will be performed over a total of about fifteen (15) samples, which includes the fresh, activated and used catalysts. Depending on the facility available at PNNL, catalyst activation under syngas will be performed either in situ or ex situ.
The data analysis using appropriate computer software will also be performed at EMSL facility. The hyperfine parameters such as the isomer shift, the quadrupole splitting, and the magnetic hyperfine field will be obtained from the Mossbauer line positions. Similarly, the peak position and the surface composition will be determined from the XPS data of each sample.
The proposed activity is expected to require 5-10 work days at EMSL. Upon approval of this proposal, the proposer will submit the samples to the EMSL experts Dr.Ravi Kukkadapu, and Mr.Mark Engelhard for Mossbauer and XPS analysis, respectively a week before the start of the activity. The proposer will visit the EMSL and assist the experts in carrying out the experiments.
Project Details
Project type
Exploratory Research
Start Date
2007-02-13
End Date
2007-09-26
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
1 S.K.Gangwal, Velu Subramani, and David A Green. Evaluation of a Long-Term Fischer-Tropsch Test and the Resulting Spent Iron Catalyst. AIChE Spring Meeting, April 23, 2007, Houston, Texas, USA