Heterogenized bimetallic clusters: their structures and bifunctional catalysis

Ichikawa, Masaru; Rao, Ling-Fen; Kimura, Takuma; Fukuoka, Atsushi

doi:10.1016/0304-5102(90)85236-b

Cited by 72 publications

(27 citation statements)

References 62 publications

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“…Similarly, Co-Ru clusters supported in zeolites NaY and NaX prepared from Ru 3 Co 3 C(CO) 14 , RuCo 2 (CO) 11 , and HRuCo 3 (CO) 12 precursors show higher activity and selectivity for the formation of C 1 -C 5 alcohols than samples incorporating only one metal [65]. For crotonaldehyde hydrogenation, g-Al 2 O 3 -supported Pt-W catalysts are found to be more active for the formation of crotyl alcohol than monometallic catalysts without W. The same behavior has been observed for other SiO 2 -supported Fe-Pt, Fe-Rh, and Fe-Ir bimetallics derived from metal carbonyl clusters [70], and is associated with the presence of heteroatomic metal1-metal2 bimetallic sites in the catalysts which due to their close proximity and their strong interaction with each other not only minimize aggregation of the components, but also provides the adequate site for the stabilization of reactive intermediates. The interaction between metal centers in bimetallic clusters does not always lead to an increase in catalytic activity in comparison to the analogous monometallic noble metal catalyst, as illustrated by the SiO 2 -supported Cu-Pt and SiO 2 -supported Pt-Au catalysts prepared from molecular metal cluster precursors, which showed a catalytic activity of about 6-30 times less than that observed for Pt/SiO 2 during toluene hydrogenation [71].…”

Section: Catalysissupporting

confidence: 74%

Well-Defined Metallic and Bimetallic Clusters Supported on Oxides and Zeolites

Guzmán

2009

Model Systems in Catalysis

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Immobilized metallic and bimetallic complexes and clusters on oxide or zeolite supports made from well-defined molecular organometallic precursors have drawn wide attention because of their novel size-dependent properties and their potential applications for catalysis. It is speculated that nearly molecular supported catalysts may combine the high activity and selectivity of homogenous catalysts with the ease of separation and robustness of operation of heterogeneous catalysts. This chapter is a review of the synthesis and physical characterization of metallic and bimetallic complexes and clusters supported on metal oxides and zeolites prepared from organometallic precursors of well-defined molecularity and stoichiometry. IntroductionRational design of catalysts guided by fundamental principles correlating composition, structure, and ligand environment with catalyst activity and selectivity has been a longstanding goal in the field of catalysis [1, 2]. Several approaches have been pursued to identify the nature of the active centers, reaction mechanisms, and the kinetics of catalytic processes, including experimental and theoretical investigations of model systems and industrial catalysts. Nevertheless, our understanding of the relationship between active center properties and catalytic performance is far from complete. Even the most thoroughly characterized supported metal catalysts prepared conventionally from salt precursors are less than well understood, because of the limitations of both the samples (nonuniformity of the metal entities) and standard characterization methods, such as N 2 -adsorption, temperature programmed reduction (TPR), etc. In the last few decades, researchers have worked toward the development and use of simple models of supported

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Section: Catalysissupporting

confidence: 74%

Well-Defined Metallic and Bimetallic Clusters Supported on Oxides and Zeolites

Guzmán

2009

Model Systems in Catalysis

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“…The models can be divided in two types, which assume either full reduction of the metal (6), or the presence of an iron oxide phase in addition to an alloy (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22); incidentally, unalloyed metals may be present as has been observed in FePd/SiO 2 (17,18).…”

Section: Discussionmentioning

confidence: 99%

“…Nevertheless, the structure of the activated FeM/SiO 2 catalysts has not yet received much attention. Proposals for the active site in methanol synthesis over bimetallic FePd and FeIr catalysts (18,20,21) implicitly rest on knowledge about the freshly reduced catalyst. This is certainly not warranted in the case of 1 : 1 FeM/SiO 2 catalysts, as the results of this paper show.…”

Section: Introductionmentioning

confidence: 99%

Structure and Reactivity of Bimetallic FeIr/SiO2 Catalysts after Reduction and during High-Pressure CO Hydrogenation

Gruijthuijsen

Howsmon

Delgass

et al. 1997

Journal of Catalysis

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Bimetallic FeIr/SiO 2 CO hydrogenation catalysts have been studied by temperature-programmed reduction, EXAFS, Mössbauer spectroscopy, and previously also by infrared spectroscopy of adsorbed CO. We concentrate on the structure of a freshly reduced sample, which is selective for the formation of hydrocarbons from CO + 3H 2 , and a catalyst activated during 48 h of reaction, which produces mainly methanol. The fresh sample contains iron oxide and bimetallic FeIr particles with an iron-rich surface after reduction in H 2 at 450 • C. During CO hydrogenation, a part of the oxidic iron reduces and forms, together with some of the iron that is initially alloyed an iron carbide. CO adsorption on activated FeIr/SiO 2 is considerably weaker than on the freshly reduced catalyst, while the activated catalyst also possesses a much higher hydrogenation activity than the initially reduced system does. Structure models for the catalyst after reduction and during steady state CO hydrogenation at high pressure are discussed.

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“…However Ichikawa et al 104 have determined the size of bimetallic particles Rh 6 x Ir x supported on NaY x D 0.6 and their distribution in the Y crystallites, and estimated their electron deficiency (metal-support interaction).…”

Section: Bimetallic Catalystsmentioning

confidence: 99%