The determination of the free-metal surface area of palladium catalysts

Schölten, J.J.F.

doi:10.1016/0021-9517(62)90012-x

Cited by 63 publications

(6 citation statements)

References 7 publications

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“…The diffraction peaks became sharper and more intense with an increase in aging temperature and aging time, which indicated the particle growth behaviors of Pd and CZ (Table 1). According to our previous study, 26 the formulation of the present catalyst, excluding Pd/A (i.e., Pd/CZ alone), showed a CZ crystallite size of 17, 24, and 45 nm after the same engine-bench aging at 800, 900, and 1000 °C, respectively, for 40 h. These values were only slightly smaller than those calculated from S BET (26,34, and 53 nm), which suggests that nearly every CZ particle consisted of a single CZ crystallite. Notably, these CZ crystallite sizes were close to those of the present Pd/CZA catalysts shown in Table 1.…”

Section: Nanoscale Structure Of Engine-bench Agedsupporting

confidence: 44%

Kinetics-Based Prediction for Sintering of Pd/CeO₂–ZrO₂–Al₂O₃ Three-Way Catalysts during Engine-Bench Aging

Iwashita

Fujiwara

Yoshida

et al. 2023

Ind. Eng. Chem. Res.

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The thermal deactivation of Pd/CeO2–ZrO2–Al2O3 (Pd/CZA) three-way catalysts (TWCs) was studied using a full-sized washcoated monolithic honeycomb after engine-bench aging at 600–1000 °C under a stoichiometric-lean-rich cycling gas condition. This was followed by chassis dynamometer driving tests. The nanoscale structure of these aged catalysts was characterized by gas adsorption, X-ray diffraction, and electron microscopy imaging to elucidate the thermal deactivation mechanism. Aging at high temperatures and for long periods facilitated the Pd particle growth via surface migration and coalescence, which caused a drop in the number of active sites and thus the catalytic activity. The detailed particle growth kinetics was analyzed using simulated laboratory-scale aging of Pd/CZA powder samples at different temperatures (700–1000 °C) and periods of time (0–40 h). The as-obtained Pd particle size vs time data were successfully fitted by applying the Finke–Watzky model with two-step agglomeration, which provided the rate constants for the initial slow growth and the subsequent faster growth. The temperature dependence of the as-obtained rate constants showed simple Arrhenius-type behavior, which was expressed using the optimized frequency factor and activation energy for the Pd particle growth. Furthermore, these results were roughly consistent with the data obtained by the engine-bench aging test for the monolithic honeycomb catalysts. The sintering kinetic model developed in the present study will be useful for the prediction of TWC deactivation and lifetime.

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Section: Nanoscale Structure Of Engine-bench Agedsupporting

confidence: 44%

Kinetics-Based Prediction for Sintering of Pd/CeO₂–ZrO₂–Al₂O₃ Three-Way Catalysts during Engine-Bench Aging

Iwashita

Fujiwara

Yoshida

et al. 2023

Ind. Eng. Chem. Res.

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“…In order to calculate the dispersion D (that is, the atomic ratio between the number of surface Pd atoms (Pd s ) and the number of total Pd atoms) from CO chemisorption measurements, the stoichiometric ratio CO/Pd s has to be known. It has been shown that CO chemisorption on Pd can occur in two ways (17,18): a carbon monoxide molecule can be bonded through the carbon to one Pd atom (linear CO) or to two Pd atoms (bridged CO). The ratio of linearly held CO to bridged-bonded CO decreases as the dispersion decreases (19,20) and the result of this is an increase in the global ratio CO/Pd s with dispersion.…”

Section: Synthesismentioning

confidence: 99%

Pd/SiO2-Cogelled Aerogel Catalysts and Impregnated Aerogel and Xerogel Catalysts: Synthesis and Characterization

Heinrichs

Noville

Pirard

1997

Journal of Catalysis

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“…A review on surface area measurements by Farrauto (1974) gives details on the chemisorption method, and the article by Pulvermacher and Ruckenstein (1974) provides details on the other methods including magnetic measurements. Of these methods, gas chemisorption is perhaps the most accurate and certainly the easiest to implement, e.g., Hz on Pt (Spenadel and Boudart, 1960;Adler and Kearney, 1960) and on Ni (Taylor, Yates and Sinfelt, 1964), CO on Pd (Scholten and Montfoort, 1962), and NO on oxides of Cu, N, and Fe (Gandhi and Shelef, 1973). While the chemisorption method is a powerful tool for catalytic research, it has its limitations for the determination of active surface area.…”

Section: Introductionmentioning

confidence: 99%

Determination of catalyst surface area from desorption characteristics of physisorbed gases

Miller

Lee

1984

AIChE Journal

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A new experimental method for the measurement of catalyst surface area of supported catalysts has been developed using selective physisorption. The desorption characteristics of a gas are studied separately on the catalyst, the support, and the supported catalyst by carrying out thermal desorption experiments in a continuous flow sorptometer. Differences in the coverage vs. temperature curves, obtained from the thermal desorption experiments, are a measure of the selectivity of the physisorbing gas, and allow calculation of the fraction of total surface area occupied by the catalyst.Two systems have been studied utilizing the thermal desorption with carbon dioxide as adsorbate: potassium carbonate/carbon black and silver/alumina. Supported catalyst surface area was determined for each system; the results were confirmed using physical mixtures of the two components (where the actual area of each component is known) and oxygen chemisorption for the silver/alumina system. The experimental technique allows for straightforward calculation of the catalyst area. D. J. MILLER and H. H. LEE Department of Chemical EngineeringUniversity of Florida Gainesville, FL 3261 1The exposed surface area of a catalyst on a support is an important parameter in the characterization of catalytic behavior, particularly in sintering and dispersion studies. Several experimental methods of determining catalyst area have been developed, including chemisorption, electron microscopy, and X-ray techniques. The difficulties involved in applying electron microscopy to actual catalysts and the sophistication of small angle X-ray scattering prevent their practical application in many cases. Chemisorption techniques have met with success in several catalyst systems, but the chemisorption techniques are limited to well-defined metal catalysts and are not in general applicable to nonmetallic catalysts. This paper presents a new method for determining catalyst area using physical adsorption. The method examines the adsorption characteristics of a gas separately on the catalyst (in powder or gauze form), the support, and the supported catalyst using a thermal desorption technique for the determination of the total exposed catalyst area as a fraction of the total catalyst and support area. This method has several advantages over other methods used in catalyst area measurements:1) The physisorption experiments are easy to carry out and the equipment needed is low cost. The physisorption experiments show good reproducibility, and sample preparation is the same as in conventional physisorption.2) The method can be applied to any catalyst system with the appropriate choice of adsorbing gas, since gases physisorb on all surfaces at low temperatures. This is in contrast to chemisorption, where the specific gas-solid interactions limit application to a few systems.3) The total catalyst area is determined directly from the experiments. Unlike chemisorption, there is no need to know the adsorption stoichiometry to determine the total area. CONCLUSIONS AND SIGNIFIC...

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The determination of the free-metal surface area of palladium catalysts

Cited by 63 publications

References 7 publications

Kinetics-Based Prediction for Sintering of Pd/CeO₂–ZrO₂–Al₂O₃ Three-Way Catalysts during Engine-Bench Aging

Kinetics-Based Prediction for Sintering of Pd/CeO₂–ZrO₂–Al₂O₃ Three-Way Catalysts during Engine-Bench Aging

Pd/SiO2-Cogelled Aerogel Catalysts and Impregnated Aerogel and Xerogel Catalysts: Synthesis and Characterization

Determination of catalyst surface area from desorption characteristics of physisorbed gases

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The determination of the free-metal surface area of palladium catalysts

Cited by 63 publications

References 7 publications

Kinetics-Based Prediction for Sintering of Pd/CeO2–ZrO2–Al2O3 Three-Way Catalysts during Engine-Bench Aging

Kinetics-Based Prediction for Sintering of Pd/CeO2–ZrO2–Al2O3 Three-Way Catalysts during Engine-Bench Aging

Pd/SiO2-Cogelled Aerogel Catalysts and Impregnated Aerogel and Xerogel Catalysts: Synthesis and Characterization

Determination of catalyst surface area from desorption characteristics of physisorbed gases

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Kinetics-Based Prediction for Sintering of Pd/CeO₂–ZrO₂–Al₂O₃ Three-Way Catalysts during Engine-Bench Aging

Kinetics-Based Prediction for Sintering of Pd/CeO₂–ZrO₂–Al₂O₃ Three-Way Catalysts during Engine-Bench Aging