The molecular basis of heterogeneous catalysis

Ronney, John J.

doi:10.1016/0304-5102(85)85056-2

Cited by 60 publications

(5 citation statements)

References 30 publications

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“…The extreme dependence of C−H activation by gaseous MO + (M = Ln or An) on the specific identity of M indicates pivotal involvement of the metal center. The following simplified activation process for the example of ThO + + cyclohexene is postulated by analogy with that proposed for solid metal oxide and gaseous SO 2 catalyzed cis − trans isomerization of 2-butene: The postulated intermediate in eq 2b comprises a metal center π-bonded to the η 3 -allylic π-delocalized anionic moiety (incorporated in a C 6 ring). The speculated participation of 5f orbitals in organometallic π-bonding in complexes such as that in eq 2b could account for the greater dehydrogenation activity of ThO + compared with CeO + .…”

Section: Resultsmentioning

confidence: 99%

Gas-Phase f-Element Organometallic Chemistry: Reactions of Cyclic Hydrocarbons with Th⁺, U⁺, ThO⁺, UO⁺, and Lanthanide Ions, Ln⁺

Gibson

1997

Organometallics

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The extent of reaction of metal ions, M+, with organic molecules depends upon the electronic structure of the metal ion; in particular, the degree to which laser-ablated lanthanide ions, Ln+, dehydrogenate hydrocarbons is known to reflect the energy needed to excite ground state Ln+ to a divalent configuration. Reported here are gas-phase reactions of Ln+ and AnO n + (An = Th or U; n = 0 or 1) with C6 and C8 cyclic hydrocarbons. The reactivities of Ln+ with c-C8H8+2 m (m = 0, 2, or 4) were consistent with previous results for Ln+ + c-C6H6+2 m , in that the relative dehydrogenation efficiencies reflected the metal ion electronic structure and excitation energy. Additionally, the relatively strong bonding between Ln+ and cyclooctatetraene (COT) was manifested as abundant condensation adduct, Ln+−COT. The dehydrogenation reactivities of Th+ and U+ with both C6 and C8 cyclic hydrocarbons were found to be comparable to that of Ce+, the most reactive Ln+, consistent with divalent An+ electronic configurations and a dehydrogenation mechanism initiated by oxidative insertion of An+ into a C−H bond. The most conspicuous discrepancy between the actinide and lanthanide results was the significant dehydrogenation reactivities of the AnO+, this in sharp contrast to essentially inert behavior of all LnO+ studied. In view of the similarity between Ce and Th, the substantial reactivity of ThO+ in light of the inert behavior of CeO+ is particularly intriguing and suggests a central role of the metal center in the dehydrogenation process. The activity of the AnO+ may reflect the distinctive nature of the 5f valence orbitals and could be partly attributable to relativistic effects. An ancillary result of the present investigation was the identification of several metal oxide clusters comprising uranium in multiple valence states.

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Section: Resultsmentioning

confidence: 99%

Gas-Phase f-Element Organometallic Chemistry: Reactions of Cyclic Hydrocarbons with Th⁺, U⁺, ThO⁺, UO⁺, and Lanthanide Ions, Ln⁺

Gibson

1997

Organometallics

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“…Alkyl halides have recently received a great deal of attention, because they are important precursors of alkyl fragments . Since these fragments play an important role in Fischer−Tropsch synthesis, oil refining, and in the transformation of methane into other hydrocarbons, − their surface chemistry on metals is of particular interest. Several recent studies have focused on the adsorption and subsequent decomposition of iodomethane on metals that include Ag(111), Au(100), Ni(100), Ni(111), Cu(110), Cu(111), Pt(111), Pd(100), Ru(001), and W(100) …”

Section: Introductionmentioning

confidence: 99%

Adsorption and Decomposition of Methyl Iodide on Low Index Planes of NiAl

Chaturvedi

Strongin

1997

Langmuir

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Surface chemistry of CD3I (CH3I) on the (111), (100), and (110) planes of NiAl has been investigated with X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). On the basis of XPS, adsorption of CD3I on the (110) and (111) planes is primarily associative at 120 K. In contrast, adsorption of the majority of the reactant on the NiAl(100) plane at 120 K is dissociative. This enhanced dissociation on NiAl(100) is attributed to its Al terminated surface. In addition to molecular CD3I desorption, TPD shows that CD4 and D2 are reaction products that desorb from the NiAl planes during the reaction of CD3I. TPD also suggests that methyl radical, CD3, may result during the thermal decomposition of CD3I on all three NiAl surfaces. Some C−C bond formation leading to the desorption of CD2CD2 is experimentally observed to occur on the (111) plane that exposes both Ni and Al atoms in the outermost surface.

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“…A Reexamination of the Thermal Decomposition Mechanism of Isobutyl Iodide on Al(111). The β-hydride elimination reaction is a common decomposition pathway for metal-bound alkyl groups with β hydrogen atoms. − ,− It was concluded on the basis of the results reported in our earlier study 21 that most alkyl groups on aluminum surfaces also follow this decomposition pathway. The evidence supporting this conclusion stemmed from the fact that only three significant types of desorption products were detected by TPRS for a variety of alkyl iodides.…”

Section: Resultsmentioning

confidence: 82%

“…Understanding the mechanisms of the reactions of alkyl groups on surfaces is important because of the centrality of such intermediates in a variety of technologically important processes as diverse as heterogeneous catalysis − and the chemical vapor deposition (CVD) of metals from organometallic precursors. − The generation of these transient species by the dissociative chemisorption of alkyl halides on metal surfaces has proven to be a useful procedure for forming these intermediates, and numerous studies employing this preparation method have been reported in recent years Al, , Cu, and Ni ) have demonstrated that the dominant thermolytic reaction pathway is β-hydride elimination, which results in the formation of the corresponding alkene and adsorbed hydrogen.…”

Section: Introductionmentioning

confidence: 99%

Direct Organometallic Synthesis: The Metal-Etching Reactions of Isobutyl Iodide on Al(111)¹

et al. 1998

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We report a study of the thermal decomposition and reactions of isobutyl iodide on Al(111). Using temperature-programmed reaction and Auger electron spectroscopies, it was found that more than one product-forming pathway involving the alkyl moiety exists on this surface. A first-order, β-hydride elimination reaction converts surface-bound isobutyl groups derived from the dissociation of the C−I bond to gas phase isobutene and dihydrogen at temperatures above ∼420 K. Competing with this unimolecular process is a collection of complex associative reactions which effect the etching of the aluminum surface via the formation of volatile organometallic species. This includes formation and subsequent desorption of diisobutylaluminum iodide (desorption peak maximum at ∼490 K), diisobutylaluminum hydride (∼515 K), methylaluminum dihydride (∼725 K), and AlI x , x = 1−3 (∼620 K). The kinetics of the processes yielding the various aluminum hydrides are coupled to that of the β-hydride elimination pathway (which serves as the hydrogen atom source) and are strongly coverage dependent. The formation of MeAlH2 reveals the occurrence of a kinetically competitive β-methyl elimination reaction of the surface alkyl groups.

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The molecular basis of heterogeneous catalysis

Cited by 60 publications

References 30 publications

Gas-Phase f-Element Organometallic Chemistry: Reactions of Cyclic Hydrocarbons with Th⁺, U⁺, ThO⁺, UO⁺, and Lanthanide Ions, Ln⁺

Gas-Phase f-Element Organometallic Chemistry: Reactions of Cyclic Hydrocarbons with Th⁺, U⁺, ThO⁺, UO⁺, and Lanthanide Ions, Ln⁺

Adsorption and Decomposition of Methyl Iodide on Low Index Planes of NiAl

Direct Organometallic Synthesis: The Metal-Etching Reactions of Isobutyl Iodide on Al(111)¹

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The molecular basis of heterogeneous catalysis

Cited by 60 publications

References 30 publications

Gas-Phase f-Element Organometallic Chemistry: Reactions of Cyclic Hydrocarbons with Th+, U+, ThO+, UO+, and Lanthanide Ions, Ln+

Gas-Phase f-Element Organometallic Chemistry: Reactions of Cyclic Hydrocarbons with Th+, U+, ThO+, UO+, and Lanthanide Ions, Ln+

Adsorption and Decomposition of Methyl Iodide on Low Index Planes of NiAl

Direct Organometallic Synthesis: The Metal-Etching Reactions of Isobutyl Iodide on Al(111)1

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Gas-Phase f-Element Organometallic Chemistry: Reactions of Cyclic Hydrocarbons with Th⁺, U⁺, ThO⁺, UO⁺, and Lanthanide Ions, Ln⁺

Gas-Phase f-Element Organometallic Chemistry: Reactions of Cyclic Hydrocarbons with Th⁺, U⁺, ThO⁺, UO⁺, and Lanthanide Ions, Ln⁺

Direct Organometallic Synthesis: The Metal-Etching Reactions of Isobutyl Iodide on Al(111)¹