skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Fischer-Tropsch Synthesis: XANES Investigation of Hydrogen Chloride Poisoned Iron and Cobalt-Based Catalysts at the K-Edges of Cl, Fe, and Co

Abstract

The effect of co-fed hydrogen chloride (HCl) in syngas on the performance of iron and cobalt-based Fischer-Tropsch (FT) catalysts was investigated in our earlier studies [ACS Catal. 5 (2015) 3124-3136 and DOE final report 2011; Catal. Lett. 144 (2014) 1127-1133]. For an iron catalyst, lower HCl concentrations (< 2.0 ppmw of HCl)) in syngas did not significantly affect the activity, whereas rapid deactivation occurred at higher concentrations (~20 ppmw). With cobalt catalysts, even low concentrations of HCl (100 ppbw) caused catalyst deactivation, and the deactivation rate increased with increasing HCl concentration in the syngas. The deactivation of the catalysts is explained by the chloride being adsorbed on the catalyst surface to (1) block the active sites and/or (2) electronically modify the sites. In this study, XANES spectroscopy was employed to investigate HCl poisoning mechanism on the iron and cobalt catalysts. Cl K-edge normalized XANES results indicate that Cl is indeed present on the catalyst following HCl poisoning and exhibits a structure similar to the family of compounds MCl; two main peaks are formed, with the second peak consisting of a main peak and a higher energy shoulder. At the Co K and Fe K edges, the white line was observedmore » to be slightly increased relative to the same catalyst under clean conditions. There is then the additional possibility that Cl adsorption may act in part to intercept electron density from the FT metallic function (e.g.,cobalt or iron carbide). If so, this would result in less back-donation and therefore hinder the scission of molecules such as CO.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [2];  [3];  [3];  [1]
  1. Univ. of Kentucky, Lexington, KY (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. Canadian Light Sources, Inc., Saskatoon, SK (Canada)
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1340425
Report Number(s):
BNL-113340-2016-JA
Journal ID: ISSN 1011-372X
Grant/Contract Number:
SC00112704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Catalysis Letters
Additional Journal Information:
Journal Volume: 146; Journal Issue: 10; Journal ID: ISSN 1011-372X
Publisher:
Springer
Country of Publication:
United States
Language:
English
Subject:
10 SYNTHETIC FUELS; Fischer-Tropsch synthesis; iron; cobalt; hydrogen chloride; activity; selectivity; XANES

Citation Formats

Pendyala, Venkat Ramana Rao, Jacobs, Gary, Ma, Wenping, Sparks, Dennis E., Shafer, Wilson D., Khalid, Syed, Xiao, Qunfeng, Hu, Yongfeng, and Davis, Burtron H.. Fischer-Tropsch Synthesis: XANES Investigation of Hydrogen Chloride Poisoned Iron and Cobalt-Based Catalysts at the K-Edges of Cl, Fe, and Co. United States: N. p., 2016. Web. doi:10.1007/s10562-016-1820-8.
Pendyala, Venkat Ramana Rao, Jacobs, Gary, Ma, Wenping, Sparks, Dennis E., Shafer, Wilson D., Khalid, Syed, Xiao, Qunfeng, Hu, Yongfeng, & Davis, Burtron H.. Fischer-Tropsch Synthesis: XANES Investigation of Hydrogen Chloride Poisoned Iron and Cobalt-Based Catalysts at the K-Edges of Cl, Fe, and Co. United States. doi:10.1007/s10562-016-1820-8.
Pendyala, Venkat Ramana Rao, Jacobs, Gary, Ma, Wenping, Sparks, Dennis E., Shafer, Wilson D., Khalid, Syed, Xiao, Qunfeng, Hu, Yongfeng, and Davis, Burtron H.. 2016. "Fischer-Tropsch Synthesis: XANES Investigation of Hydrogen Chloride Poisoned Iron and Cobalt-Based Catalysts at the K-Edges of Cl, Fe, and Co". United States. doi:10.1007/s10562-016-1820-8. https://www.osti.gov/servlets/purl/1340425.
@article{osti_1340425,
title = {Fischer-Tropsch Synthesis: XANES Investigation of Hydrogen Chloride Poisoned Iron and Cobalt-Based Catalysts at the K-Edges of Cl, Fe, and Co},
author = {Pendyala, Venkat Ramana Rao and Jacobs, Gary and Ma, Wenping and Sparks, Dennis E. and Shafer, Wilson D. and Khalid, Syed and Xiao, Qunfeng and Hu, Yongfeng and Davis, Burtron H.},
abstractNote = {The effect of co-fed hydrogen chloride (HCl) in syngas on the performance of iron and cobalt-based Fischer-Tropsch (FT) catalysts was investigated in our earlier studies [ACS Catal. 5 (2015) 3124-3136 and DOE final report 2011; Catal. Lett. 144 (2014) 1127-1133]. For an iron catalyst, lower HCl concentrations (< 2.0 ppmw of HCl)) in syngas did not significantly affect the activity, whereas rapid deactivation occurred at higher concentrations (~20 ppmw). With cobalt catalysts, even low concentrations of HCl (100 ppbw) caused catalyst deactivation, and the deactivation rate increased with increasing HCl concentration in the syngas. The deactivation of the catalysts is explained by the chloride being adsorbed on the catalyst surface to (1) block the active sites and/or (2) electronically modify the sites. In this study, XANES spectroscopy was employed to investigate HCl poisoning mechanism on the iron and cobalt catalysts. Cl K-edge normalized XANES results indicate that Cl is indeed present on the catalyst following HCl poisoning and exhibits a structure similar to the family of compounds MCl; two main peaks are formed, with the second peak consisting of a main peak and a higher energy shoulder. At the Co K and Fe K edges, the white line was observed to be slightly increased relative to the same catalyst under clean conditions. There is then the additional possibility that Cl adsorption may act in part to intercept electron density from the FT metallic function (e.g.,cobalt or iron carbide). If so, this would result in less back-donation and therefore hinder the scission of molecules such as CO.},
doi = {10.1007/s10562-016-1820-8},
journal = {Catalysis Letters},
number = 10,
volume = 146,
place = {United States},
year = 2016,
month = 7
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Save / Share:
  • The promoting impact of alkali metals (i.e., Li, Na, K, Rb, Cs) on the carburization rate of Fe in Fe/Si catalysts was investigated by X-ray absorption spectroscopy. A multisample holder was used, allowing nearly simultaneous examination of the catalysts during activation in a CO/He mixture. With the white line intensity and shape as a fingerprint for oxidation state, TPR/XANES analysis enabled us to measure the relative composition of the different compounds as a function of the carburization time, temperature, and atomic number of the group 1 promoter. At the same time, TPR/EXAFS provided information on the changes in local atomicmore » structure that accompanied the oxidation state changes. The rate of carburization increased in the following order: unpromoted < Li < Na < K = Rb = Cs. After 10 h of treatment the samples containing K, Rb, and Cs were completely carburized, and residual quantities of iron oxides were detected in both unpromoted and Li-promoted samples. The EXAFS spectra after carburization could be fitted well by considering a model containing Hagg carbide and Fe{sub 3}O{sub 4}. After 10 h of CO/He treatment at 290 C, the main component observed was Hagg carbide. A model containing Hagg and {var_epsilon}-carbides, and Fe{sub 3}O{sub 4}, was also investigated. However, the r-factor was not significantly impacted by including {var_epsilon}-carbide in the fitting, and the resulting contribution of {var_epsilon}-carbide in each catalyst from the model was virtually negligible. Selectivity differences are thus not likely due to changes in the carbide distribution. Rather, the alkali promoter increases the CO dissociative adsorption rate, resulting in an increase in the surface coverage of dissociated CO and an inhibition in the olefin readsorption rate. This in turn results in higher olefin selectivities, in agreement with previous catalytic tests.« less
  • Fe-based catalysts containing different amounts of Mn were tested for Fischer-Tropsch synthesis using a stirred tank reactor at 270 C, 1.21 MPa, and H{sub 2}:CO = 0.7. Catalyst activation by carburization with 10% CO/He was followed by Temperature Programmed Reduction/X-ray Absorption Spectroscopy (TPR-EXAFS/XANES) from room temperature to 300 C. {gamma}-Fe{sub 2}O{sub 3} was converted into iron carbides, whereas MnO{sub x} was reduced to oxygen deficient MnO. Mn hindered Fe carburization, such that the carburized catalyst displayed higher Fe{sub 3}O{sub 4} content than the catalyst without Mn. EXAFS fitting indicates that the carburized catalyst contained a mixture of Hgg carbide, Fe{submore » 3}O{sub 4}, and Mn oxides. Increasing Mn content led to higher CH{sub 4} and light product selectivities, and lower light olefin selectivities. Higher and stable conversions were obtained with a catalyst containing an almost equimolar Fe/Mn ratio relative to the catalyst without Mn. Selectivity trends are attributed to the higher WGS rates observed on the FeMn catalysts, consistent with the structural differences observed.« less
  • Coal-to-liquids. Iron-based Fischer-Tropsch synthesis catalysts are not only used commercially for high temperature Fischer-Tropsch synthesis, but are increasingly becoming the focus for converting low H{sub 2}/CO ratio synthesis gas at lower temperature. Such low temperature processing yields hydrocarbon distributions with higher {alpha} values, and as a consequence, much less light hydrocarbon gas production (and especially, less methane). Another benefit to the use of iron-based catalysts is that the product slate is richer in {alpha}-olefinic products, which are more valuable than the paraffinic products produced using cobalt-based catalysts. Iron-based catalysts are often used to convert low H{sub 2}/CO ratio syngas, becausemore » the catalysts can intrinsically adjust the syngas ratio upward by converting a fraction of CO by reaction with H{sub 2}O to produce H{sub 2} and CO{sub 2} via the water-gas shift reaction.« less
  • The authors have examined hydrocarbon chain growth in the Fischer-Tropsch reaction by following both the rate and position of incorporation of /sup 13/C into the hydrocarbon products after an abrupt switch from /sup 12/CO to /sup 13/CO in the reactant gas. On two catalysts (cobalt supported on silica and precipitated iron combined with various promoters) they find that /sup 13/C appears after the isotope switch at the same rate in all positions of all products examined. Under the assumption that chain growth is unidirectional, this finding shows that chain growth on these catalysts is very rapid in comparison to themore » rate of isotope displacement in the precursors to chain growth. In addition, only a small portion of the active carbon on the surface can be in the form of hydrocarbon chains. Under these conditions no detailed information about the mechanism of chain growth is obtainable.« less