Surface-Chlorinated Ceria and Chlorine-Containing Reduced Pd/CeO<sub>2</sub> Catalysts. A FTIR Study

Badri, Ahmed; Binet, Claude; Lavalley, Jean‐Claude

doi:10.1021/jp953023m

“…Chlorine is not known to interact with the electrolyte material, however interactions with ceria, gold, silver, and platinum have been documented. 46 Both gold and platinum form stable chlorides at high temperature, however unlike nickel, these materials do not sublimate under conditions relevant for the studies performed in this work. 42 Chlorine also adsorbs to ceria, affecting catalytic activity and conductivity.…”

Section: Discussionmentioning

confidence: 95%

“…42 Chlorine also adsorbs to ceria, affecting catalytic activity and conductivity. 46 Because none of these processes permanently affect the fuel cell, the high frequency impedance including R bulk recovered fully following removal of CH 3 Cl from the incident fuel feed. The same behavior was not observed for the changes to the polarization arcs observed in the Nyquist plots (Fig.…”

Section: Discussionmentioning

confidence: 99%

In Operando Vibrational Raman Studies of Chlorine Contamination in Solid Oxide Fuel Cells

Reeping

¹

,

Walker

²

2015

J. Electrochem. Soc.

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Vibrational Raman spectroscopy coupled with voltammetry and impedance measurements was used to explore the effects of chlorine on solid oxide fuel cell (SOFC) performance and durability. SOFC anodes were exposed to 110 ppm dry CH 3 Cl at 650 • C for up to four hours while intermittently exposing the cell to methane for ten minute intervals. In these experiments Raman spectroscopy was used to monitor carbon accumulation kinetics. Electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurements performed under CH 4 following 1 hour of exposure to CH 3 Cl showed marked degradation. This degradation was less apparent when the SOFC was operated with H 2 in the presence of CH 3 Cl. With methane and CH 3 Cl, peak power diminished at a rate of 14% per hour. Observable carbon accumulation during CH 3 Cl exposure became less pronounced over time. Eventually, carbon formation was suppressed completely suggesting that the primary effect of the Cl contaminant was deactivation of the Ni catalyst with respect to CH bond dissociation. SOFC performance with H 2 in the presence of CH 3 Cl remained largely unchanged. Interestingly, these effects of Cl on SOFC performance with methane proved partially reversible as electrochemical performance and carbon accumulation behavior were recovered upon removal of the CH 3 Cl from the fuel feed. Solid oxide fuel cells are electricity-generating devices capable of fuel-to-electricity conversion efficiencies of more than 80% when combined with heating applications.1-3 These efficiencies far outpace even the most modern fossil fuel fired power plants. 4 In addition, the high operating temperatures of solid oxide fuel cells (SOFCs) allow operation with many different fuels including biogas, syngas, natural gas, gasoline and even some alcohols.5-8 However, this versatility comes at the cost of having to develop SOFC materials capable of withstanding impurities intrinsic to each fuel type. These impurities include, but are not limited to, carbon deposits, sulfur, chlorine, silicon, phosphorus, and mercury. Each can cause premature degradation of SOFC materials.6,9-15 Many, if not all, of these impurities have been studied extensively using electrochemical methods. Techniques such as electrochemical impedance spectroscopy (EIS) and voltammetry consistently show how exposure to these individual contaminants lead to performance degradation with differing levels of severity and reversibility. However, while the electrochemical results quantify overall cell degradation, direct, in-situ evidence of the mechanisms responsible for diminished performance remain speculative. Coupling electrochemical methods with in-situ optical spectroscopy, such as Raman spectroscopy or XPS, advances understanding of the reactions that occur on the SOFC electrode surfaces as well as how those reactions affect performance. Raman spectroscopy has already shown to be a promising technique for high temperature in-situ characterization of molecules on the surface of an SOFC operating on hydrocarbon ...

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“…The presence of the band at 2032 cm -1 may suggest the presence of defect sites which were able to activate the CO molecule on the Cl-free catalyst, these sites being likely candidates to promote the CO oxidation reaction. Badri et al [50] also observed a similar shift in the CO band induced by chlorine species. In agreement with these results, this shift was due to the formation of an active electronegative species by chlorine.…”

Section: Co Prox: Effect Of Feed Compositionmentioning

confidence: 66%

“…Apparently, those oxygen vacancies at the metalsupport interface favor the activation of the CO molecule and provide active sites for the oxidation to CO 2 [49]. On the contrary, in the chlorinated catalyst, chlorine inhibited the formation of those oxygen vacancies due to the formation of CeOCl surface species [22,50,51]. This process was favored at high reduction temperatures.…”

Section: Co Prox: Effect Of Reaction and Reduction Temperaturementioning

confidence: 99%

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Influence of the metal precursor on the catalytic behavior of Pt/Ceria catalysts in the preferential oxidation of CO in the presence of H2 (PROX)

Jardim

¹

,

Rico-Francés

²

,

Coloma

³

et al. 2015

Journal of Colloid and Interface Science

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The effect of the metal precursor (presence or absence of chlorine) on the preferential oxidation of CO in the presence of H2 over Pt/CeO2 catalysts has been studied. The catalysts were prepared using (Pt(NH3)4)(NO3)2 and H2PtCl6, as precursors, in order to ascertain the effect of the chlorine species on the chemical properties of the support and on the catalytic behavior of these systems in the PROX reaction. The results show that chloride species exert an important effect on the redox properties of the oxide support due to surface chlorination. Consequently, the chlorinated catalyst exhibits a poorer catalytic activity at low temperatures compared with the chlorine-free catalyst, and this is accompanied by a higher selectivity to CO2 even at high reaction temperatures. It is proposed that the CO oxidation mechanism follows different pathways on each catalyst. This is a previous version of the article published in Journal of Colloid and Interface Science. 2015, 443: 45-55. doi:10.1016/j.jcis.2014 3: Graphical Abstract (for review)• The presence or absence of Cl in the Pt precursor strongly affects the catalytic behavior.• The Pt precursor affects the PROX mechanism at low reaction temperatures.• At 333 K, the mechanism in the Cl-free catalyst seems to involve the -OH groups on the support.• At higher temperatures, the reaction occurs via the same mechanism on both catalysts.. Highlights (for review) AbstractThe effect of the metal precursor (presence or absence of chlorine) on the preferential oxidation of CO in the presence of H 2 over Pt/CeO 2 catalysts has been studied. The catalysts are prepared using (Pt(NH 3 ) 4 )(NO 3 ) 2 and H 2 PtCl 6 , as precursors, in order to ascertain the effect of the chlorine species on the chemical properties of the support and on the catalytic behavior of these systems in the PROX reaction. The results show that chloride species exert an important effect on the redox properties of the oxide support due to surface chlorination. Consequently, the chlorinated catalyst exhibits a poorer catalytic activity at low temperatures compared with the chlorine-free catalyst, and this is accompanied by a higher selectivity to CO 2 even at high reaction temperatures. It is proposed that the CO oxidation mechanism follows different pathways on each catalyst.

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Vibrational Spectroscopy in the Study of Oxide (Excluding Zeolites) and Sulfide Catalysts

Payen

¹

,

Grimblot

²

,

Lavalley³

et al. 2001

Handbook of Vibrational Spectroscopy

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The sections in this article are Introduction Infrared Spectroscopy IR Characterization of Surface Properties of Metal Oxides Information Deriving from the Activated Oxide Spectra Lattice Vibrations Surface Oxide Sites Identification of Main Impurities in Metal Oxides Electronic Transitions Hydroxyl Groups Information Deriving from Probe Adsorption Acidity Basicity Cationic and Redox Sites: Use of Methanol as Probe for Local Arrangement and Oxidation State Determination of Surface Cationic Sites IR Characterization of Oxide and Sulfide Supported Catalysts Information Deriving from the Spectrum of the Activated Catalyst Information Deriving from Probe Molecule Adsorption CUS Characterization of the Sulfided Phase B rønsted Acid Site Characterization of the Sulfided Phase Site Transformation in the Presence of H 2 Surface Characterization and Catalysis Conclusion R aman Spectroscopy General Considerations Bulk Oxide Catalysts Supports Supported Oxides Nature of the Supported Oxide Chemical Processes Involved During Catalyst Synthesis Adsorption of Probe Molecules Surface B rønsted and Lewis Acid Sites Adsorption of Molecules Acting as Reagents Active Phase: Genesis and Characterization Genesis of the Hydrodesulfurization Active Phase Sulfided Catalyst Catalyst Reactivity Conclusion Concluding Remarks and Outlook

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Surface-Chlorinated Ceria and Chlorine-Containing Reduced Pd/CeO₂ Catalysts. A FTIR Study

Cited by 44 publications

References 34 publications

In Operando Vibrational Raman Studies of Chlorine Contamination in Solid Oxide Fuel Cells

In Operando Vibrational Raman Studies of Chlorine Contamination in Solid Oxide Fuel Cells

Influence of the metal precursor on the catalytic behavior of Pt/Ceria catalysts in the preferential oxidation of CO in the presence of H2 (PROX)

Vibrational Spectroscopy in the Study of Oxide (Excluding Zeolites) and Sulfide Catalysts

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Surface-Chlorinated Ceria and Chlorine-Containing Reduced Pd/CeO2 Catalysts. A FTIR Study

Cited by 44 publications

References 34 publications

In Operando Vibrational Raman Studies of Chlorine Contamination in Solid Oxide Fuel Cells

In Operando Vibrational Raman Studies of Chlorine Contamination in Solid Oxide Fuel Cells

Influence of the metal precursor on the catalytic behavior of Pt/Ceria catalysts in the preferential oxidation of CO in the presence of H2 (PROX)

Vibrational Spectroscopy in the Study of Oxide (Excluding Zeolites) and Sulfide Catalysts

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Surface-Chlorinated Ceria and Chlorine-Containing Reduced Pd/CeO₂ Catalysts. A FTIR Study