Effect of Support on the Size and Composition of Highly Dispersed Pt–Sn Particles

Bednářová, L.; Lyman, Charles E.; Rytter, Erling; Holmén, Anders

doi:10.1006/jcat.2002.3699

Cited by 40 publications

(52 citation statements)

References 35 publications

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“…This activity increase makes the system particularly suited for elucidating information on the active state of the catalyst, using in situ methods. Previous studies using ex situ TEM indicated that the metal particles are enriched in Pt during reduction, most particles containing 60-90wt% Pt [4,16]. CO adsorption measurements suggested an electronic interaction between the support material and the metal particles, leading to less CO adsorption on Pt,Sn/Mg(Al)O than expected from activity measurements of Pt,Sn/Mg(Al)O and Pt,Sn/Al 2 O 3 [15,16].…”

Section: And Refs Therein)mentioning

confidence: 91%

“…Only a few reports in the open literature have been devoted to the system under study; Pt,Sn/Mg(Al)O [4,7,15,16,25,26]. The activity pattern of a proprietary 0.25wt%Pt,0.5wt%Sn/Mg(Al)O catalyst is quite peculiar, in that the initial activity increases during repeated dehydrogenation-regeneration cycles [15].…”

Section: And Refs Therein)mentioning

confidence: 99%

“…Previous studies using ex situ TEM indicated that the metal particles are enriched in Pt during reduction, most particles containing 60-90wt% Pt [4,16]. CO adsorption measurements suggested an electronic interaction between the support material and the metal particles, leading to less CO adsorption on Pt,Sn/Mg(Al)O than expected from activity measurements of Pt,Sn/Mg(Al)O and Pt,Sn/Al 2 O 3 [15,16]. In the present study, in situ XPS was used to obtain real-time information about the distribution of Sn in the catalyst, by following the Sn/Mg ratio with time on stream during repeated dehydrogenation-regeneration cycles.…”

Section: And Refs Therein)mentioning

confidence: 99%

“…After calcination, CO 2 adsorption, followed by Temperature-Programmed Desorption (TPD) experiments, showed that the final metal clusters cover the most basic sites of the support material, i.e. steps and corners [16,27]. The Pt(Sn) clusters are likely to be distributed at step and corner sites at the outer surface as well as in the catalyst pores.…”

Section: Sample Preparation and Characterizationmentioning

confidence: 99%

“…Most studies report advantageous effects of promoting Pt catalysts with Sn: Tin promotion improves catalytic activity, dehydrogenation selectivity, prevents Pt sintering, and decreases deactivation due to coke formation (see e.g. [4,[16][17][18][19][20][21][22][23] …”

Section: Introductionmentioning

confidence: 99%

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In situ XPS investigation of Pt(Sn)/Mg(Al)O catalysts during ethane dehydrogenation experiments

et al. 2007

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Calcined hydrotalcite with or without added metal (Mg(Al)O, Pt/Mg(Al)O and Pt,Sn/Mg(Al)O) have been investigated with in situ X-ray Photoelectron Spectroscopy (XPS) during ethane dehydrogenation experiments. The temperature in the analysis chamber was 450ºC and the gas pressure was in the range 0.3 -1 mbar. Depth profiling of calcined hydrotalcite and platinum catalysts under reaction, oxidation and in hydrogenwater mixture was performed by varying the photon energy, covering an analysis depth of 10-21 Å. It was observed that the Mg/Al ratio in the Mg(Al)O crystallites does not vary significantly in the analysis depth range studied. This result indicates that Mg and Al are homogeneously distributed in the Mg(Al)O crystallites. Catalytic tests have shown that the initial activity of a Pt,Sn/Mg(Al)O catalyst increases during an activation period consisting of several cycles of reduction -dehydrogenation -oxidation. The Sn/Mg ratio in a Pt,Sn/Mg(Al)O catalyst was followed during several such cycles, and was found to increase during the activation period, probably due to a process where tin spreads over the carrier material and covers an increasing fraction of the Mg(Al)O surface. The results further indicate that spreading of tin occurs under reduction conditions. A PtSn 2 alloy was studied separately. The surface of the alloy was enriched in Sn during reduction and reaction conditions at 450°C. Binding energies were determined and indicated that Sn on the particle surface is predominantly in an oxidized state under reaction conditions, while Pt and a fraction of Sn is present as a reduced Pt-Sn alloy.

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Section: And Refs Therein)mentioning

confidence: 91%

Section: And Refs Therein)mentioning

confidence: 99%

Section: And Refs Therein)mentioning

confidence: 99%

Section: Sample Preparation and Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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In situ XPS investigation of Pt(Sn)/Mg(Al)O catalysts during ethane dehydrogenation experiments

et al. 2007

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Particle Size and Dispersion Measurements

Bergeret¹,

Gallezot²

2008

Handbook of Heterogeneous Catalysis

216

177

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The sections in this article are Definitions and Generalities Particles Particle Size Nuclearity of Particles Dispersion Relationships Between Particle Size, Surface Area and Dispersion Methods of Particle Size Measurement Particle Size Measurements by Gas Chemisorption Introduction and Principles Gas Adsorption–Desorption Methods A Static Methods B Dynamic Methods C Desorption Methods Choice of Adsorbate Gases Hydrogen Chemisorption; HydrogenOxygen Titration Conclusion and Recommendations X ‐Ray Diffraction Line Broadening Analysis Introduction Elementary Line Broadening Analysis: the Scherrer Equation Complete Line Profile Analysis: the W arren– A verbach Method Examples of Application of Classical LBA to Catalysts Whole‐Powder Pattern Fitting Methods: the Rietveld Refinement Limits of Application of Methods Conclusion Small‐Angle X ‐Ray Scattering Analysis Introduction Specific Surface Area Measurements: P orod's Law Mean Size Parameters: Guinier Radius Calculation of Size Distribution Application of SAXS to Metal Particle Size Determination in Supported Catalysts Anomalous Small‐Angle X ‐Ray Scattering ( ASAXS ) Conclusion Determination of Particle Size by Electron Microscopy Scope Fundamentals of Imaging and Contrast A Transmission Electron Microscope B Scanning Transmission Electron Microscope C Scanning Electron Microscope Preparation of Samples for TEM and STEM Examination Particle Size Measurement Selected Examples of Particle Size Distribution Selected Examples of 3D Localization of Particles in Supports by Electron Tomography Particle Size Measurements by Magnetic Methods

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Combined macroscopic, nanoscopic and atomic‐scale characterization of highly dispersed bimetallic particles supported on ceria‐zirconia mixed oxide catalysts

Chinchilla¹,

Olmos²,

Chen³

et al. 2016

European Microscopy Congress 2016: Proceedings

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Highly dispersed gold nanoparticles appear as promising catalysts in the field of fine chemistry. However, the relatively low resistance to sintering of gold particles under reaction conditions often leads to a significant loss of catalytic activity. One strategy to overcome this limitation is combining gold with another metal to form a bimetallic system with enhanced stability, activity and/or selectivity. [1] The catalytic behavior of bimetallic particles is determined by their structure, size, morphology and chemical composition. Undoubtedly, to design efficient and high‐quality catalyst requires controlling all these features during the synthesis as well as a careful characterization of the synthesized catalysts at the finest scales. Such a characterization poses demanding challenges to STEM techniques if we want it to be representative of the actual macroscopic state of the surface of the catalyst. In this work, the capabilities and limitations of both the macroscopic (XPS, XRD, ICP‐AES, and chemisorption) and atomic scale (STEM‐XEDS) techniques in the characterization of highly dispersed bimetallic particles, AuRu and AuPd, supported on a ceria‐zirconia mixed oxide (CZ) have been evaluated. In particular, the effects of the catalyst activation pretreatment on nanostructure and catalytic performance for the selective oxidation of glycerol to glyceric acid of both bimetallic systems are investigated in comparative terms. Following the approach described in [2], the relationship between composition (Au at.%), as determined by quantitative STEM‐XEDS analysis, and size, as determined by HREM and HAADF, of a large ensemble of individual nanoparticles on the two types of catalysts was established as a function of calcination temperature, Figures 1 and 2. According to size‐composition maps shown there, Figures 1(a) and 2(a), the monometallic gold particles exhibit a wider larger of sizes and a larger average size, whereas monometallic Ru or Pd particles are smaller in average. Bimetallic entities are found in the intermediate size range. Raising the temperature up to 700ºC, Figures 1 and 2 (b), induces a compositional homogenization in the case the AuPd catalysts which is not observed in the case of the AuRu bimetallics. From this point of view both catalysts behave in a quite different manner, in spite of Ru and Pd being elements very close in the Periodic Table. Comparison of data obtained on the corresponding monometallic reference catalysts clearly indicates that the second metal, Ru or Pd, moderates the sintering behavior of Au, i.e. the stability of this type of catalysts. Moreover, a significant improvement in the catalytic activity takes place in the bimetallic catalysts, which is related to the presence of bimetallic entities in both catalysts. STEM data suggest that these bimetallic nanoparticles are formed by decoration of the surface of Au nanoparticles with 3D, nanosized, domains of the second metal, instead of forming actual Au‐Ru or Au‐Pd alloys. [3,4] The limitations of STEM studies to reach a precise representation of the composition on both bimetallic systems determined by macroscopic techniques (like XPS or ICP) will also be addressed, Figure 1and 2 (c). The likely origin of such discrepancies as well as strategies to overcome this limitation will also be discussed.

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Effect of Support on the Size and Composition of Highly Dispersed Pt–Sn Particles

Cited by 40 publications

References 35 publications

In situ XPS investigation of Pt(Sn)/Mg(Al)O catalysts during ethane dehydrogenation experiments

In situ XPS investigation of Pt(Sn)/Mg(Al)O catalysts during ethane dehydrogenation experiments

Particle Size and Dispersion Measurements

Combined macroscopic, nanoscopic and atomic‐scale characterization of highly dispersed bimetallic particles supported on ceria‐zirconia mixed oxide catalysts

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