Pt clusters in BaKL zeolite: Characterization by transmission electron microscopy, hydrogen chemisorption, and X-ray absorption spectroscopy

Vaarkamp, Marius; Grondelle, J Joop van; Miller, J.T.; Sajkowski, DJ; Modica, FS; Lane, GS; Gates, B. C.; Koningsberger, DC Diek

doi:10.1007/bf00764004

Cited by 74 publications

(47 citation statements)

References 18 publications

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“…The same models were used to calculate metal dispersion based on the hydrogen chemisorption capacity. The H/Pt stoichiometry increases with decreasing particle size because smaller particles have a higher concentration of edges and corners, where more than one hydrogen atom per metal atom can adsorb, than larger particles (24,25). Thus, by using these models varying H/Pt ratios were used for calculation the Pt dispersion.…”

Section: Catalyst Characterizationsmentioning

confidence: 99%

The State of Zirconia Supported Platinum Catalysts for CO2/CH4Reforming

Bitter

Seshan

Lercher

1997

Journal of Catalysis

229

110

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In Pt/ZrO 2 catalysts used for CO 2 /CH 4 reforming to syngas, not all accessible Pt contributes equally to the activity of the catalyst. The catalytic activity is determined by the accessibility of Pt on the Pt-ZrO 2 perimeter. This is explained in terms of the CO 2 activation via carbonate species on the support which must be in the proximity of the Pt particles to react with the methane activated on the metal. The significance of the support is also emphasized by the low activity of Pt black and Pt/SiO 2 , which were incapable of forming carbonates on the support. The perimeter concentration of Pt/ZrO 2 can be changed by changing the Pt concentration in the catalyst or by increasing the calcination temperature which causes sintering of the Pt particles. In contrast to the calcination temperature, the reduction temperature did not influence the activity although the hydrogen chemisorption capacity was markedly decreased by increasing the reduction temperature. As sintering was excluded on basis of particle size determination from EXAFS results a SMSI state on Pt/ZrO 2 during high temperature reduction is concluded to exist. This state does not persist under reaction conditions due to the presence of adsorbed oxygen from CO 2 dissociation.

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Section: Catalyst Characterizationsmentioning

confidence: 99%

The State of Zirconia Supported Platinum Catalysts for CO2/CH4Reforming

Bitter

Seshan

Lercher

1997

Journal of Catalysis

229

110

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“…However, EXAFS measurements on similarly-prepared catalysts consistently find average coordination numbers ranging from 4-6, which correspond to an average particle size of 6-10 atoms [ 16,19,[21][22][23]. We have also examined similarly-prepared catalysts by TEM, observing few, if any Pt particles larger than the detection limit of about 10 ,~ [ 23,24]. While the measured H/Pt values would seem to indicate much larger particles, such large particles would be clearly visible by TEM, and this size is well outside the error limit of our EXAFS measurements.…”

Section: Hydrogen Chemisorptionmentioning

confidence: 99%

“…Although platinum particle sizes were not measured for the samples used in this study, EXAFS analysis of similarly-prepared catalysts have shown platinum particle sizes of 6-10 atoms [ 16,19,[21][22][23], and an average of 8 atoms/cluster is assumed. Other structural parameters for LTL are: 16.4 T/ 1000 ~3, 386 m2/g, 2.11 g/cm 3 [25,26].…”

Section: Tpd Experimentsmentioning

confidence: 99%

Role of spill-over hydrogen in the hydrogenolysis of neopentane

Modica¹,

Miller²,

Meyers³

et al. 1994

Catalysis Today

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A series of Pt/LTL zeolite catalysts with varying Pt loading and support acidity was studied by hydrogen temperature-programmed desorption (TPD) and reaction of neopentane and propane. Specific desorption peaks in the TPD were associated with hydrogen spilled-over onto the support. The ability of the spilled-over hydrogen to migrate on the support surface was limited to approximately 35 nm from the platinum cluster. Saturation capacity for spilled-over hydrogen was related to the support acidity/basicity, with a maximum of about 1018 atoms/m 2 for the most acidic support studied. Spilled-over hydrogen was inert to oxygen treatment at 100°C, and did not contribute to catalytic activity for neopentane or propane conversion. Instead, hydrogenolysis TOF and the amount of spilledover hydrogen were mutually dependent on support acidity/basicity. Both declined with increasing K/AI ratio of the support, and continued to decline even for basic supports with K/A1 ratios greater than 1. The continued decline in activity for K/A1 > 1 indicates than the metal-support interaction is not dependent on acidic hydroxyls.

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“…The HZSM-5 sample was found to chemisorb no detectable amount of hydrogen within experimental error. From the calibration made by Kip et al (20) and extended by Vaarkamp et al (21) it can be determined that a H/Pt value of 2.0 indicates a particle size of 2.5 to 5Å.…”

Section: Pretreatment and Hydrogen Chemisorptionmentioning

confidence: 99%