On the Mechanism of the H–D ExchangeReaction in Ethane over Platinum Catalysts

Loaiza, Alfonso; Xu, M.; Zaera, Francisco

doi:10.1006/jcat.1996.0072

Cited by 56 publications

(51 citation statements)

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“…However, some additional uncertainty is introduced in the experiment with the light alkane because of the large signals from the C 2 D 4 ϩ ion (responsible for ϳ95% of the intensity of the 16 Da peak). In any case, the results for the C 2 H 6 ϩ D 2 mixture are in excellent agreement with previous analysis using 13 C NMR (30% CD 2 HCH 3 :70% CDH 2 CDH 2 ) [7,12].…”

Section: Resultssupporting

confidence: 90%

“…It should be noted that there are alternative methods for the determination of isotopic substitutions. In particular, we were quite successful in the past with the characterization of our ethane mixtures using NMR [7,12]. Nevertheless, we see the two approaches as complementary.…”

Section: Discussionmentioning

confidence: 94%

“…Deconvolution of the data was done by using the experimental cracking patterns of the pure ethane isotopologs available to us and calculated spectra of the rest using a previously reported methodology [10]. It was found that even though the LR-MS data tends to overestimate the amount of light ethanes produced, it reproduces the overall conversion and general isotopologue distribution curves reasonably well, in particular the percentages of each of the components in terms of the total number of deuterium substitutions [7]. A U-shaped distribution was found in all cases, with maxima at one (d 1 ) and six (d 6 ) and a minimum at three (d 3 ) atoms per ethane molecule.…”

Section: Resultsmentioning

confidence: 99%

“…Two ethane mixtures were produced by H™D exchange using a platinum foil (Aldrich, Milwaukee, WI, 99.99% purity) as catalyst and a micro-batch reactor described elsewhere [7][8][9]. Mixtures of either 50 torr of normal C 2 H 6 and 500 torr of D 2 or 50 torr of C 2 D 6 and 500 torr of H 2 were reacted, at 625 and 675 K respectively, until reaching 37 and 55% total conversions.…”

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confidence: 99%

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Regiospecificity in deuterium labeling determined by mass spectrometry

Loaiza

Zaera

2004

J. Am. Soc. Mass Spectrom.

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Several mass spectrometry methods were explored to determine the regiospecificity of deuterium substitutions in hydrocarbon mixtures. The case investigated in this work was that of ethane mixtures obtained by catalytic H™D exchange between either C 2 H 6 and D 2 or C 2 D 6 and H 2 over platinum surfaces. A total of ten isotopologs are possible, and were indeed detected in all cases. Deconvolution of low-resolution mass spectra was found sufficient to determine the composition of the gas mixtures in terms of the total number of deuterium substitutions, but not to identify symmetric versus asymmetric substitutions in the C 2 D 2 H 4 , C 2 D 3 H 3 , and C 2 D 4 H 2 products. High-resolution mass spectrometry allowed the separation of the intensities due to C 2 X 4 ϩ fragments from those from molecular C 2 X 6 ϩ signals (X ϭ H or D), and with that for a more accurate determination of the composition of the mixtures. Relative probabilities were determined for the symmetric versus asymmetric removal of X 2 from C 2 X 6 ϩ ions and for isotope scrambling in the mass spectrometer, and with that information fairly good cracking patterns were then calculated for the C 2 X 4 ϩ fragments produced by each individual pure C 2 X 6 isotopologue. However, total deconvolution of all ten components in the ethane mixtures obtained by H™D exchange catalysis was beyond the experimental accuracy of the measurements. Tandem mass spectrometry/collision-induced decomposition mass spectrometry (MS/CID-MS) proved more useful for this task. In particular, it was possible to determine the proportion of symmetric versus asymmetric double H™D exchange in samples for which the total ethane-d 2 (in the case of C 2 H 6 ϩ D 2 ) or ethane-d 4 (with C 2 D 6 ϩ H 2 ) amounted to only ϳ3% on the ethane mix. A comparison with other analytical methods, NMR in particular, is provided. (J Am Soc Mass Spectrom 2004, 15, 1366 -1373

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Section: Resultssupporting

confidence: 90%

Section: Discussionmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Regiospecificity in deuterium labeling determined by mass spectrometry

Loaiza

Zaera

2004

J. Am. Soc. Mass Spectrom.

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“…The catalytic activity of the Pt-supported catalysts was investigated by using a 150-ml stainless-loop batch reactor (67,68). The composition of the gas mixture was determined periodically by gas chromatography, using a 23% SP-1700 on 80/100 Chromosorb PAW column and a flame ionization detector.…”

Section: Methodsmentioning

confidence: 99%

Synthesis of heterogeneous catalysts with well shaped platinum particles to control reaction selectivity

Lee

Morales

Albiter

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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224

173

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Colloidal and sol-gel procedures have been used to prepare heterogeneous catalysts consisting of platinum metal particles with narrow size distributions and well defined shapes dispersed on high-surface-area silica supports. The overall procedure was developed in three stages. First, tetrahedral and cubic colloidal metal particles were prepared in solution by using a procedure derived from that reported by El-Sayed and coworkers [Ahmadi TS, Wang ZL, Green TC, Henglein A, El-Sayed MA (1996) Science 272: 1924 -1926]. This method allowed size and shape to be controlled independently. Next, the colloidal particles were dispersed onto high-surface-area solids. Three approaches were attempted: (i) in situ reduction of the colloidal mixture in the presence of the support, (ii) in situ sol-gel synthesis of the support in the presence of the colloidal particles, and (iii) direct impregnation of the particles onto the support. Finally, the resulting catalysts were activated and tested for the promotion of carbon-carbon doublebond cis-trans isomerization reactions in olefins. Our results indicate that the selectivity of the reaction may be controlled by using supported catalysts with appropriate metal particle shapes. On the basis of their kinetic behavior, catalytic reactions are often classified as either mild or demanding (1-3). Demanding reactions-such as the oxidation of CO, NO, or hydrocarbons; the synthesis of ammonia; and most oil processing conversionsusually require high temperatures and pressures, and involve small concentrations of intermediates similar to those identified under vacuum. The performance of these reactions often depends strongly on the structure of the catalyst used (4, 5). In contrast, mild reactions-in particular, hydrogenations and isomerizations of unsaturated hydrocarbons-take place under less-demanding temperature and pressure conditions. Mild reactions have historically been considered structure-insensitive (6-8), but that conclusion has been drawn from studies on reactivity vs. metal dispersion that used ill-defined supported catalysts (9, 10) and has been questioned by more recent studies using better catalytic models (11). For instance, both experimental (12-14) and theoretical (15) studies on the selective catalytic hydrogenation of CAO bonds in unsaturated aldehydes have suggested that such reactions may be promoted by close-packed (111) surfaces. In another example, the dehydrogenation of cyclohexene was found to be faster on Pt (111) than on Pt (100) single-crystal surfaces (16). Our recent surface-science investigations on the isomerization of unsaturated olefins (17-19) strongly suggest that selectivity toward the formation of the cis isomer may be favored by Pt (111) facets. Additional surfacescience reports on the conversion of alkyl and alkene adsorbates under vacuum conditions (20-25), as well as studies with more realistic model systems (26, 27), point to a potential structure sensitivity in the conversion of other olefins and unsaturated hydrocarbons.These results not only s...

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Surface‐Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal Nanocatalysts

Zhang¹,

Lee²,

Ge³

et al. 2010

Adv Funct Materials

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221

197

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Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general “encapsulation and etching” strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface‐protected etching process, both yolk–shell and core–satellite type nanoreactors are synthesized and their utilization in liquid‐ and gas‐phase catalysis is demonstrated. The thermal and chemical stability of the metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework.

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On the Mechanism of the H–D ExchangeReaction in Ethane over Platinum Catalysts

Cited by 56 publications

References 0 publications

Regiospecificity in deuterium labeling determined by mass spectrometry

Regiospecificity in deuterium labeling determined by mass spectrometry

Synthesis of heterogeneous catalysts with well shaped platinum particles to control reaction selectivity

Surface‐Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal Nanocatalysts

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