Water gas shift activity and kinetics of Pt/Re catalysts supported on ceria-zirconia oxides

Radhakrishnan, Rakesh; Willigan, Rhonda; Dardas, Zissis; Vanderspurt, Thomas H.

doi:10.1016/j.apcatb.2006.02.017

Cited by 71 publications

(36 citation statements)

References 8 publications

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“…Ceria-supported metals have received a great deal of attention in recent years because they can exhibit high activities for the water-gas-shift (WGS) [1][2][3][4][5][6][7] and steamreforming reactions [8][9][10][11]. While there is still some debate over the role that ceria plays in these reactions [12,13], one of the leading proposals is that ceria, because of its ability to cycle between the ?3 and ?4 oxidation states, donates oxygen to the metal for oxidation of the CO or hydrocarbons and then is re-oxidized by the steam [5].…”

Section: Introductionmentioning

confidence: 99%

The Water–Gas-Shift Reaction on Pd/Ceria–Praseodymia: The Effect of Redox Thermodynamics

et al. 2009

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Reaction rates for the water-gas-shift (WGS) reaction were measured on catalysts with 1-wt% Pd supported on CeO 2 , Ce 0.5 Pr 0.5 O 2-x and PrO x in order to determine whether the weakly bound oxygen associated with Pr could enhance reaction rates. However, differential rates in 25 Torr of both CO and H 2 O showed that the activity of Pr-containing catalysts were much lower. Measurements of the oxygen content of these samples after reduction in dry H 2 at 873 K, after reoxidation in steam at 873 K, and following exposure of the catalysts to WGS conditions at 873 K demonstrate that ceria is easily reoxidized by steam and remains oxidized under WGS conditions, while the loosely bound oxygen associated with praseodymia or ceria-praseodymia is lost under WGS conditions and cannot be restored by oxidation in steam. These results can be understood by comparing the equilibrium redox properties of the support materials to the typical P(O 2 ) experienced under WGS conditions.

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Section: Introductionmentioning

confidence: 99%

The Water–Gas-Shift Reaction on Pd/Ceria–Praseodymia: The Effect of Redox Thermodynamics

et al. 2009

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“…The WGSR catalysts were selected from the literature [37][38][39][40][41] and their elemental compositions followed the optimized results reported in the corresponding studies.…”

Section: Preparation Of Catalystsmentioning

confidence: 99%

“…The preparation of Pt-Re/CeO 2 -ZrO 2 (PRCZ) followed the ''urea homogeneous crystallization co-precipitation method'' [39,40]. The targeted amounts of cerium and zirconium nitrates (atomic ratio, Ce:Zr = 58:42) were dissolved separately in deionized water and mixed together with urea under vigorous stirring.…”

Section: Preparation Of Catalystsmentioning

confidence: 99%

Passive NOx Reduction with CO Using Pd/TiO2/Al2O3 + WGSR Catalysts Under Simulated Post-Euro IV Diesel Exhaust Conditions

Hong

Lee

et al. 2010

Catal Lett

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This study deals with diesel DeNO x catalysis by physically mixed Pd/TiO 2 /Al 2 O 3 and water-gas-shiftreaction (WGSR) catalysts under CO-rich conditions at a CO/NO x ratio of 16. In the post-Euro IV era, many diesel engines are expected to produce CO-rich exhaust emissions due to the trend toward emission regulation and limitations in related technologies. Under these circumstances, the passive DeNO x strategy utilizing CO as a single reductant can be considered appropriate. The Pd/TiO 2 /Al 2 O 3 catalyst is well known for its high DeNO x performance when CO and H 2 are available as NO x reductants. However, when CO is used as a single reductant, the catalyst shows poor DeNO x activity, even if the CO concentration is exceptionally high (CO/NO x = 16). In this study, the DeNO x activity of Pd/TiO 2 /Al 2 O 3 was noticeably improved by physically mixing it with a proper WGSR catalyst (Cu/ZnO/Al 2 O 3 ), which is capable of producing H 2 and feeding it to Pd/TiO 2 /Al 2 O 3 successfully even in the presence of O 2 . The NO x conversion exceeded 70% at 400-450°C using a Pdcatalyst mixture at a weight ratio of 33:67. The reaction gas consisted of 500 ppm NO, 8000 ppm CO, 8 vol.% O 2 , 5 vol.% CO 2 and 10 vol.% H 2 O and w/f was 0.1 g s/cm 3 .

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“…More recently, these catalysts (PtRe) have been demonstrated to provide nearly two times the activity for the WGSR (Eq. 1) than platinum by itself [10,11]. While the actual mechanism is not well understood, it is believed the promotion is partly the result of increased platinum dispersion.…”

Section: Introductionmentioning

confidence: 95%

Deactivation, Regeneration, and Stable Performance of a PtMoRe Water Gas Shift Catalyst for On-Site Hydrogen Generation: Part 2

D'Orazio

Ruettinger²,

Castaldi

et al. 2008

Top Catal

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This paper analyzes the mechanism of deactivation and methods of regeneration of a PtMoRe water gas shift catalyst supported on a stabilized zirconia. Although this catalyst initially possesses high activity below 250°C, a decrease in CO conversion ranging from 10 to 50% was observed over a period of 60 h. To determine the mechanism responsible for the decay, a series of activity tests and high resolution transmission electron microscopy analyses were done. Experimental results revealed the existence of stable and unstable operating regimes that depend on the reaction temperature, CO concentration, and H 2 O/H 2 . The high initial activity of this catalyst relies upon a synergetic relationship between the platinum, molybdenum, and rhenium which form an alloy generating the catalytically active phase. Based on our experimental results, we have concluded water contained in the feed gas oxidizes the Mo/ Re metals, disrupts this synergy (de-alloys), and deactivates the catalyst. While not completely understood, CO is required for this oxidation mechanism to occur and possible explanations are discussed. Heating the catalyst in a hydrogen or reformate gas reduces the oxides back to metals, reforms the PtMoRe alloy, and restores the activity of the catalyst. Conditions for stable performance are consistent with use as a mid-temperature range water gas shift catalyst for on-site hydrogen generation.

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Water gas shift activity and kinetics of Pt/Re catalysts supported on ceria-zirconia oxides

Cited by 71 publications

References 8 publications

The Water–Gas-Shift Reaction on Pd/Ceria–Praseodymia: The Effect of Redox Thermodynamics

The Water–Gas-Shift Reaction on Pd/Ceria–Praseodymia: The Effect of Redox Thermodynamics

Passive NOx Reduction with CO Using Pd/TiO2/Al2O3 + WGSR Catalysts Under Simulated Post-Euro IV Diesel Exhaust Conditions

Deactivation, Regeneration, and Stable Performance of a PtMoRe Water Gas Shift Catalyst for On-Site Hydrogen Generation: Part 2

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