Particle size determination of supported catalytic metals: Platinum on silica gel

Adams, Charles R.; Benesi, H. A.; Curtis, R. M.; Meisenheimer, R.G.

doi:10.1016/0021-9517(62)90061-1

Cited by 93 publications

(10 citation statements)

References 5 publications

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“…% Pt on alumina prepared and characterized by Ostermaier ( 1973; Ostermaier et al, 1974a). The unsintered catalyst had a platinum dispersion of 0.38 corresponding to a surface average platinum crystallite size of 2.7 nm assuming a cube with five sides available for hydrogen chemisorption (Adams et al, 1962) and a 1:l hydrogen atom to surface platinum atom stoichiometry (Wilson andHall, 1970, 1972). It chemisorbed 9.83 x 10-6 gmole Hz/g cat.…”

Section: Methodsmentioning

confidence: 99%

Molecular oxygen induced crystallite size effect in reduction of nitric oxide with ammonia ober supported platinum

1974

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The effect of changing platinum crystallite size from 2.7 to 15.5 nm on the specific catalytic activity in NO reduction by NH3, with and without added O2, was studied over alumina supported platinum catalysts between 423 and 473°K. In the NO‐NH3 system both specific catalytic activity and selectivity to N2 are independent of crystallite size. In the NO‐O2‐NH3 system the specific catalytic activity of the 15.5 nm crystallites is about six times that of the 2.7 nm crystallites. The NO reduction rate shows dependence on NO to the first power and on NH3 to the one‐half power.

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Section: Methodsmentioning

confidence: 99%

Molecular oxygen induced crystallite size effect in reduction of nitric oxide with ammonia ober supported platinum

1974

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“…The silicalite particle sizes ranged from 0.8 to about 1.8 pm for Catalysts 1 to 8. The surface average diameter (Adams et al, 1962) of the silicalite crystals for Catalysts 1 to 8 was 1.3 pm. Submicron sized silicalite crystals were used for Catalysts 9 and 10.…”

Section: Resultsmentioning

confidence: 93%

Preparation and characterization of Pt/silicalite catalysts with high Pt loadings

et al. 1988

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Methods for preparing Pt/silicalite catalysts are described. Equilibration of silicalite, a pentasil zeolite, in aqueous solutions of Pt(NH3), Cl2 containing excess ammonia resulted in Pt/silicalite catalysts with Pt loadings of ≥7 wt%. The Pt/silicalite catalysts were characterized by hydrogen chemisorption, X‐ray diffraction and transmission electron microscopy. The characterization studies showed that the majority of the Pt in the heavily loaded catalysts was located in the silicalite pores, and the Pt dispersions in these catalysts exceeded 0.8.

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“…The XRD Pd size estimate is a volumetric average technique and the result should be larger than the estimate from chemisorption, which is a surface average technique, while both techniques are weighted towards larger particles. The Pd particles in Table 2 were 21 nm or less and within the size range in the literature of 2-33 nm where crystallite length is synonymous with particle size, as those works used electron microscopy and chemisorption for confirmation [44,45,46,47]. Note that crystallite length can be smaller than particle size if large particles are made of agglomerated crystals of if any poorly crystalline regions exist in the particle.…”

Section: Average Pd Size Comparisonmentioning

confidence: 88%

Pd model catalysts: Effect of aging duration on lean redispersion

Lupescu

Schwank

Fisher

et al. 2016

Applied Catalysis B: Environmental

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An automotive three-way catalyst (TWC) deteriorates as a function of temperature, time and aging environment. While much effort has gone into formulating durable exhaust catalysts, relatively little attention has been paid to controlling the aging environment on the vehicle with techniques currently in use to protect the catalyst and counteract the increasing demands for higher fuel economy (e.g., overfueling to reduce exhaust temperatures). New engine control methods that are designed to minimize aging may be possible that can reduce the extent of catalyst deactivation and provide a lean environment capable of redispersing many of the precious metal particles. To develop improved engine control methods, detailed experimental information is needed to map the response of the catalyst to different aging conditions. In this report, we examine palladium-based model powder catalysts on ceria-zirconia, which were exposed to three different exhaust compositions, lean-only, rich-only and redox, each at 700°C for three different durations, 20 minutes, 2 hours and 16 hours. Residual catalyst activity and metal-support interaction were probed with Water Gas Shift (WGS) reaction and Oxygen Storage Capacity (OSC) measurements. The Pd metal particle size and dispersion were estimated by H 2 chemisorption and XRD line broadening. Lean catalyst treatments at 550°C and 700°C were applied to determine the effect on Pd size and catalyst activity. An infrared study of CO adsorption onto the catalysts was used to identify whether Pd crystallite facets were covered by the support after exposure to the redox aging environment then again after the lean treatments were applied. The aging temperature and reducing gas environment significantly deteriorated catalytic activity through a combination of metal oxidation state effects and support interactions, while the aging duration was linked to the extent of Pd sintering reversibility through lean treatments. These insights provide a basis to develop engine control and aftertreatment design strategies to avoid severe aging modes and determine how often to actively intervene to regenerate the catalyst.

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Particle size determination of supported catalytic metals: Platinum on silica gel

Cited by 93 publications

References 5 publications

Molecular oxygen induced crystallite size effect in reduction of nitric oxide with ammonia ober supported platinum

Molecular oxygen induced crystallite size effect in reduction of nitric oxide with ammonia ober supported platinum

Preparation and characterization of Pt/silicalite catalysts with high Pt loadings

Pd model catalysts: Effect of aging duration on lean redispersion

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