On the specific activity of platinum catalysts

Boudart, M.; Aldag, A.W.; Benson, John; Dougharty, Neil A.; Harkins, C.G.

doi:10.1016/0021-9517(66)90113-8

Cited by 307 publications

(146 citation statements)

References 20 publications

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“…For the second triad metals, ruthenium, rhodium, and palladium, the specific activity passes through a small maximum at rhodium in position 2 of group VIII. This pattern is remarkably similar to that observed by Dalla Betta et al (21) for the hydrogenation of cyclopropane, a reaction termed facile by Boudart et al (22). The activity pattern is very different for reactions such as the hydrogenolysis of ethane, where activities fall steeply in each triad with increasing atomic number (21).…”

Section: Discussionsupporting

confidence: 86%

Hydrogen–Water Deuterium Exchange over Graphon Supported Group VIII Noble Metals

Sagert¹,

Pouteau²

1973

Can. J. Chem.

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Specific activities of Group VIII noble metals supported on Graphon have been determined for hydrogen-water deuterium exchange. Metal surface areas, which are required to calculate specific activities, were measured by hydrogen chemisorption, and by reaction of hydrogen with chemisorbed oxygen. For the second triad metals, ruthenium, rhodium, and palladium, and in the temperature range 140 to 225 "C, the variation of activity was R u < R h > Pd. For the third triad metals, osmium, iridium, and platinum, the variation of activities was O s < I r < Pt in the same range of temperature. Apparent activation energies were measured over this temperature range, and orders of reaction with respect to hydrogen and water were measured at 160 "C (200 "C for Pt). From these data, activation energies for the surface exchange reaction were calculated. In the second triad the activation energies decrease slightly with increasing atomic number, but in the third triad they decrease quite markedly with increasing atomic number. A good correlation was obtained between the activation energy for surface exchange and the thermionic work function of the metal. This supports our earlier suggestion that Graphon is able to donate electrons to the metal and thus lower the activation energy for the surface exchange.L'activite specifique de metaux nobles du groupe VIII fixes sur Graphon a it6 determinee pour I'Cchange de deuterium H,-HDO. La superficie de la surface mitallique, qui est necessaire lors du calcul des activites specifiques, a kt6 Cvaluee a I'aide de la chemisorption de I'hydrogene ainsi qu'a I'aide d e la reaction de I'hydrogene avec de I'oxygene chemisorbe. Pour la seconde triade de metaux, ruthenium, rhodium et palladium, et dans I'intervalle de temperatures allant de 140 a 225 "C, la variation d'activite a ete dans I'ordre Ru < Rh > Pd. Pour la troisieme triade de metaux, osmium, iridium et platine, la variation d'activite a e t t dans I'ordre 0 s < Ir < Pt dans le m&me intervalle de temperatures. Les Cnergies apparentes d'activation ont etC mesurees pour cet intervalle de temperatures alors que I'ordre des reactions par rapport a I'hydrogene et a l'eau a ete determine a 160 "C (200 "C pour le Pt). A partir d e ces donnees, on a calcule pour les reactions d'echange se faisant en surface les energies d'activation. Dans la seconde tr~ade, les energies d'activation diminuent lkgerement selon I'ordre croissant des nurneros atomiques, alors que dans la troisieme triade elles diminuent selon I'ordre croissant des numeros atomiques d'une f a~o n assez marquee. Une bonne correlation a ete obtenue entre I'energie d'activation pour I'Cchange en surface et la fonction du travail thermionique du metal. Ce fait est en accord avec nos suggestions antirieurs voulant que le Graphon est capable de donner des electrons au metal et ainsi diminuer I'Cnergie d'activation necessaire a l'echange en surface.[Traduit par le journal] Can. J. Chem., 51,4031 (1973) Introduction Group VIII metals have been shown to be good catalysts for most hydrogen...

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Section: Discussionsupporting

confidence: 86%

Hydrogen–Water Deuterium Exchange over Graphon Supported Group VIII Noble Metals

Sagert¹,

Pouteau²

1973

Can. J. Chem.

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“…18 wt% for all catalysts, compared to the nominal loading of 20 wt%. [Boudart 1966] and Pt/SiO 2 [Boudart 1966, Oteroschipper 1977 show the values to be in agreement within the same order of magnitude, which is very good considering differences in catalyst preparation, composition, and reaction conditions. The apparent activation energy (E app ) of 11.9 kcal/mol measured for the non-modified Pt/C catalyst is in agreement with what has been reported in the literature for Pt catalysts.…”

Section: Catalyst Characterizationsupporting

confidence: 58%

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

Goodwin¹,

Colón-Mercado²,

Hongsirikarn³

et al. 2011

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EXECUTIVE SUMMARYThe main objectives of this project were to investigate the effect of a series of potential impurities on fuel cell operation and on the particular components of the fuel cell MEA, to propose (where possible) mechanism(s) by which these impurities affected fuel cell performance, and to suggest strategies for minimizing these impurity effects. This project was carried out primarily at Clemson University and the Savannah River National Lab. Fuel cell investigations were done at SRNL while all investigations of the MEA components were carried out at Clemson. Meetings took place weekly at Clemson University and at SRNL with the respective project participants. Joint meetings between researchers at Clemson and SRNL took place quarterly, on average. In addition, frequent communications among project participants took place via e-mail and telephone discussions. On other occasions the researchers met with the technical staff of John Deere for discussions. At least one member of our team routinely participated in the DOE-Sponsored Joint Hydrogen Quality Task Force Meetings (usually conducted monthly).The nature and concentrations of impurities investigated and their impact on fuel cell performance and individual components are given in the table below. The negative effect on Pt/C was to decrease hydrogen surface coverage and hydrogen activation at fuel cell conditions. The negative effect on Nafion components was to decrease proton conductivity, primarily by replacing/reacting with the protons on the Bronsted acid sites of the Nafion.Even though already well known as fuel cell poisons, the effects of CO and NH 3 were studied in great detail early on in the project in order to develop methodology for evaluating poisoning effects in general, to help establish reproducibility of results among a number of laboratories in the U.S. investigating impurity effects, and to help establish lower limit standards for impurities during hydrogen production for fuel cell utilization.New methodologies developed included (1) a means to measure hydrogen surface concentration on the Pt catalyst (HDSAP) before and after exposure to impurities, (2) a way to predict conductivity of a Nafion membranes exposed to impurities using a characteristic acid catalyzed reaction (methanol esterification of acetic acid), and, more importantly, (3) application of the latter technique to predict conductivity on Nafion in the catalyst layer of the MEA. H 2 -D 2 exchange was found to be suitable for predicting hydrogen activation of Pt catalysts.Using a combination of standard catalyst characterization techniques, a structure sensitive catalytic reaction technique (cyclopropane hydrogenolysis), and reaction and transport modeling led to the finding that in the catalyst layer (essentially Nafion/Pt/C) the following best describes the structure. Pt is highly dispersed on the C support, but primarily in the meso-and macropores. The Nafion (ca. 30 wt%) resides primarily on the external surface of the C support where it blocks significant numbers ...

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“…Apparently any electronic changes as the particle size is reduced do not affect the specific rate coefficient. This behavior seems common to a number of reactions such as H2-D, exchange (24), hydrogenations (24-26), dehydrogenations (26), and some simple hydrogenolyses (27). Conversely the isomerization of neopentane (6) is known to be demanding and shows a particle size effect.…”

Section: Discussionmentioning

confidence: 86%

The Specific Activity of Silica Supported Platinum for the Catalysis of Hydrogen–Methane Deuterium Exchange

Sagert¹,

Pouteau²

1973

Can. J. Chem.

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Rate data are reported as a function of temperature for the exchange of D, with CH4 over a number of platinum-silica catalysts. Two different methods of preparing catalysts, impregnation and ion exchange, were used to get two series of metal particle sizes. Within each series, the particle size was increased by sintering batches in air at temperatures to 800 "C. These methods produced platinum particles ranging from 0.9 to 10 nni diameter. The metal surface areas were measured by hydrogen chemisorption and, where possible, by X-ray diffraction and electron nlicroscopy.The specific rate coefficients or rate coefficients per unit surface area of platinum varied by a factor of up to 40 within each series and reached a maximum for sintering temperatures of about 500°C. The maximum specific rate coefficients for CH4 conversion at 200 "C, and total pressure of 60 k N m-,, were 1.3 and 1.9 x mol CH, m -2 s-' for the ion-exchanged and impregnated catalysts respectively. Activation energies were in the range 60 to 100 kJ m~l -~. Since a relatively small change in specific rate coefficient was noted between the two series as compared to the changes within each series, no large effect of particle size on the specific rate coefficient was demonstrated. The different specific rate coefficients within the series are ascribed to other effects of sintering, particularly the formation of the lower energy Pt(ll1) surface. Some evidence was noted for a particle size eRect in the distribution of products, with more multiple exchange being observed for the smallest particles.Les donnees de vitesse en fonction de la temperature pour 1'Cchange de D, avec CH, s u r un certain nombre de catalyseurs platine-silice ont ete rapportees. Deux methodes differentes de preparation des catalyseurs (par impregnation et par echange ionique) ont tte utilistes pour obtenir deux types de tailles pour les particules mCtalliques. Dans chaque type, les dimensions des particules ont Cte accrues par une operation de frittage dans I'air i des temperatures allant jusqu'i 800 "C. Ces methodes conduisent a

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On the specific activity of platinum catalysts

Cited by 307 publications

References 20 publications

Hydrogen–Water Deuterium Exchange over Graphon Supported Group VIII Noble Metals

Hydrogen–Water Deuterium Exchange over Graphon Supported Group VIII Noble Metals

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

The Specific Activity of Silica Supported Platinum for the Catalysis of Hydrogen–Methane Deuterium Exchange

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