Finite size effects on supported Pd nanoparticles: Interaction of hydrogen with CO and C2H4

Morkel, Matthias; Rupprechter, Günther; Freund, Hans‐Joachim

doi:10.1016/j.susc.2005.05.037

Cited by 86 publications

(88 citation statements)

References 57 publications

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“…A similar increase was observed on Ru(001) [107]. C x H y fragments from ethylidyne decomposition were also more stable in the presence of adsorbed CO which suggests that CO inhibits C-C bond cleavage by a mechanism in which CO blocks highly reactive decomposition sites and a repulsive CO-C 2 D x interaction which reduces the M-C 2 D x binding strength [108]. These observations suggest that carbon monoxide may play a more complicated role in catalysis than merely site blocking but may also influence the binding strength of other surface species (reactants and intermediates) such that it is no longer optimal.…”

Section: Coadsorption Of Carbon Monoxide and Ethylene On Pt Catalystssupporting

confidence: 64%

“…These observations suggest that carbon monoxide may play a more complicated role in catalysis than merely site blocking but may also influence the binding strength of other surface species (reactants and intermediates) such that it is no longer optimal. Co-adsorption studies of ethylene and CO or NO on Rh (111) demonstrate that the small inorganic molecules adsorb on their favored sites, while ethylidyne is left to adsorb on less favored sites, which supports the thermal desorption behavior of carbon monoxide on mixed adsorbate surfaces; CO desorption from an ethylidyne covered was unchanged relative to CO adsorbed on the same clean surface [106][107][108]. However, it is difficult to explain the increased stability of ethylidyne if it is displaced from favored adsorption sites but the proposed mechanism for ethylidyne decomposition suggest that up to 6 atoms [72] are needed and the statistically probability of six vacant atoms coalescing near an adsorbed ethylidyne molecule is small.…”

Section: Coadsorption Of Carbon Monoxide and Ethylene On Pt Catalystsmentioning

confidence: 62%

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The Synthesis, Characterization and Catalytic Reaction Studies of Monodisperse Platinum Nanoparticles in Mesoporous Oxide Materials

Rioux

2006

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A catalyst design program was implemented in which Pt nanoparticles, either of monodisperse size and/or shape were synthesized, characterized and studied in a number of hydrocarbon conversion reactions. The novel preparation of these materials enables exquisite control over their physical and chemical properties that could be controlled (and therefore rationally tuned) during synthesis. The ability to synthesize rather than prepare catalysts followed by thorough characterization enable accurate structure-function relationships to be elucidated. Pt nanoparticles (1.7-7.1 nm) are synthesized by solution phase reduction methods in which Pt precursors are reduced in protic solvents in the presence of a surface templating polymer, which serves to stabilize the metal nanoparticles in solution. Particle size can be controlled during synthesis by altering either the PVP: Pt salt ratio, reaction media and by seeded growth methods. After Pt nanoparticles are synthesized, their size and morphology are confirmed with transmission electron microscopy and x-ray diffraction. Low power sonication in either aqueous or 2 organic solvent was utilized to disperse Pt nanoparticles within the mesoporous metal oxide matrix. This method of catalyst synthesis is named capillary inclusion (CI). An alternative approach to catalyst synthesis combines the hydrothermal synthesis of mesoporous silica with Pt nanoparticle synthesis in the same solution. Synthesis under neutral conditions led to a catalyst in which the nanoparticles were highly dispersed throughout the catalyst matrix. This method of catalyst synthesis called nanoparticle encapsulation (NE) ensured that Pt nanoparticles were located on the internal pore surface of the mesoporous silica. Catalysts were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), small angle x-ray scattering (SAXS) and physical adsorption to determine metal particle size and mesoporous structure. The surface chemistry of the nanoparticle surface was studied by infrared spectroscopy, selective gas adsorption (chemisorption) and catalytic reactivity studies. During nanoparticle synthesis, PVP is added to the solution to stabilize the platinum nanoparticles against aggregation. This polymer remains bound to the nanoparticle surface after catalyst synthesis and must be removed before catalytic reactions.Calcination of the catalyst at high temperature (623-723 K) for long time periods (24-36 hours) followed by reduction was initially used to clean the Pt surface. While calcination-reduction treatment is a standard procedure for catalyst activation, the need for long treatments was due to the high molecular weight (~55,000) of the surfacestabilizing polymer. Polymer removal was confirmed by selective gas adsorption, infrared spectroscopy investigation of CO adsorption as well as ethylene hydrogenation.Metallic surface area determined by chemisorption was not in agreement with XRD or TEM results and turnover rates for ethylene hydrogenation results were lower than those 3 measured o...

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Section: Coadsorption Of Carbon Monoxide and Ethylene On Pt Catalystssupporting

confidence: 64%

Section: Coadsorption Of Carbon Monoxide and Ethylene On Pt Catalystsmentioning

confidence: 62%

The Synthesis, Characterization and Catalytic Reaction Studies of Monodisperse Platinum Nanoparticles in Mesoporous Oxide Materials

Rioux

2006

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“…In addition to the presence of neighboring Pd atoms, the formation of palladium hydrides under hydrogenation reaction conditions substantially influences the selectivity. Reducing the amount of hydrogen incorporated in the catalyst diminishes the hydrogen supply for the hydrogenation reaction and increases the selectivity of acetylene hydrogenation to ethylene [17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Palladium–gallium intermetallic compounds for the selective hydrogenation of acetylenePart I: Preparation and structural investigation under reaction conditions

Osswald

Giedigkeit

Jentoft

et al. 2008

Journal of Catalysis

280

221

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The intermetallic compounds PdGa and Pd 3 Ga 7 are introduced as selective catalysts for the hydrogenation of acetylene. Single phase PdGa and Pd 3 Ga 7 can readily be prepared by the appropriate thermal treatment of the stoichiometric mixtures of the corresponding elements. The initial low surface areas of the as-prepared materials can be increased by careful mechanical treatment without decomposition. Detailed investigations of PdGa and Pd 3 Ga 7 by DSC/TG, in situ powder X-ray diffraction and in situ X-ray absorption spectroscopy during thermal treatment under various inert or reactive gas atmospheres showed a high thermal stability. The long-range and short-range order in the crystal structures remained intact up to temperatures of about 600 K. Neither phase transitions nor decomposition were detectable. In addition to high thermal stability -preserving the active-site isolation under reaction conditions -no incorporation of hydrogen or carbon in the intermetallic compounds under reducing conditions was observed. Besides being interesting model systems, palladium gallium intermetallic compounds are promising candidates for the application as highly selective hydrogenation catalysts.

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“…Because Pd catalysts are used in many reactions involving hydrogen (e.g., hydrogenation of CO [23], [24], [25], [26] and [27] and of CO 2 [28], [29], [30] and [31], methanol synthesis [27], [28] and [31]), the presence of Pd hydrides may have a pronounced effect on catalyst performance [10] and [22]. Pd hydride formation has been reported to either suppress catalytic activity or favor catalytic performance; examples include the enhancement of hydrogenation of alkynes [10] and ethene [32] and the suppression of hydrogenation of cyclohexenes [10]. Altogether, detailed knowledge of the formation of Pd hydrides and of their structural and thermal stability will be of value in understanding the foregoing catalytic processes.…”

Section: Introductionmentioning

confidence: 99%

Hydride formation and stability on a Pd–SiO2 thin-film model catalyst studied by TEM and SAED

Jenewein¹,

Penner²,

Gabasch³

et al. 2006

Journal of Catalysis

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Hydride formation was studied on Pd particles supported on SiO 2 , and the results were evaluated with reference to a corresponding ZnO-promoted Pd/SiO 2 catalyst reported recently. Pd particles (mean size, ~5 nm) were epitaxially grown on NaCl(001) cleavage faces and subsequently covered by a layer of amorphous SiO 2 , thereby maintaining their epitaxial orientation. The films were subjected to various hydrogen and annealing treatments in the temperature regime of 373-873 K, and their stability in an O 2 environment (373-573 K) was also tested. The structural and morphological changes were followed by transmission electron microscopy and selected area electron diffraction. Reduction at 523 K increased the mean particle size considerably and converted the Pd particles into an amorphous hydride phase that decomposed at and above 673 K either by reduction in hydrogen or by annealing in He environment, forming a crystalline Pd 2 Si phase. Oxidative treatments of the Pd-H phase at temperatures above 523 K induce transformation into partially oriented Pd particles. The Pd 2 Si phase was stable under reductive conditions up to 873 K and decomposed into disoriented Pd particles on oxidation at temperatures at and above 573 K. Although the Pd/SiO 2 catalyst can be readily converted into an amorphous hydride phase, it loses its hydrogen storage capability on entering the silicide state at 673 K, and hence no hydride formation was observed. These results are in contrast to previous observations on a corresponding Pd/ZnO/SiO 2 catalyst, where the formation of a well-ordered PdZn alloy prevented the formation of the hydride phase and significantly enhanced the structural stability of the catalyst and its resistance against sintering. In contrast, the Pd/SiO 2 system was converted into the amorphous hydride state under "real" catalytic conditions, for example, during CO 2 hydrogenation at around 523 K.

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Finite size effects on supported Pd nanoparticles: Interaction of hydrogen with CO and C2H4

Cited by 86 publications

References 57 publications

The Synthesis, Characterization and Catalytic Reaction Studies of Monodisperse Platinum Nanoparticles in Mesoporous Oxide Materials

The Synthesis, Characterization and Catalytic Reaction Studies of Monodisperse Platinum Nanoparticles in Mesoporous Oxide Materials

Palladium–gallium intermetallic compounds for the selective hydrogenation of acetylenePart I: Preparation and structural investigation under reaction conditions

Hydride formation and stability on a Pd–SiO2 thin-film model catalyst studied by TEM and SAED

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