Mono- and bimetallic colloidal particles have gained increasing attention in science and application throughout the last several years. In this contribution, we present a synopsis of the wet chemical syntheses of these materials and survey potential applications in catalysis and materials science. Methods for the characterization of these particles and their surfaces are not reviewed here.

Nanoscopic Metal Particles − Synthetic Methods and Potential Applications

Publisher Summary Alloying of a catalytically active metal with an inert component changes the selectivity in hydrocarbon reactions such that C–C bond fission is suppressed compared with C–H bond breaking. Upon alloying, the selectivity for cracking reactions decreases. This chapter shows that the surface composition of macroscopic alloys often differs from the bulk composition. Selectivity changes can be understood in terms of the primary ensemble effect—that is, the dilution of the metal surface with inactive atoms diminishes the probability for metal-adsorbate complexes containing several neighboring metal atoms as required for cracking. The concept of an ensemble of metal atoms, crucial to the understanding of selectivity patterns on alloys, implies that the metal atoms in the surface of the alloy keep their individuality and are only influenced by their immediate environment. The chapter discusses the secondary ensemble effect that ascribes changes in heat of chemisorption of multiply bonded atoms to a decrease in the coordination of these atoms to the surface metal atoms. This effect leads to a decrease in heat of adsorption upon alloying.

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Surface Composition and Selectivity of Alloy Catalysts

Heavily doped semiconductors have recently emerged as a remarkable class of plasmonic alternative to conventional noble metals; however, controlled manipulation of their surface plasmon bands toward short wavelengths, especially in the visible light spectrum, still remains a challenge. Here we demonstrate that hydrogen doped given MoO3 and WO3 via a facile H-spillover approach, namely, hydrogen bronzes, exhibit strong localized surface plasmon resonances in the visible light region. Through variation of their stoichiometric compositions, tunable plasmon resonances could be observed in a wide range, which hinge upon the reduction temperatures, metal species, the nature and the size of metal oxide supports in the synthetic H2 reduction process as well as oxidation treatment in the postsynthetic process. Density functional theory calculations unravel that the intercalation of hydrogen atoms into the given host structures yields appreciable delocalized electrons, enabling their plasmonic properties. The plasm...

Hydrogen Doped Metal Oxide Semiconductors with Exceptional and Tunable Localized Surface Plasmon Resonances.

Publisher Summary This chapter discusses the catalysis by alloys in hydrocarbon reactions. With solution alloys the effect of alloying on the electronic structure is surprisingly small, and also with intermetallic compounds these effects are not very pronounced. The effect of alloying on catalytic reactions depends very much on the mechanism of the catalytic reaction and on the type of intermediates operating upon reaction. In parallel-running, simultaneous reactions, the alloying effect is very pronounced if in order for a reaction to occur, large ensembles of certain metal atoms are required. However, the fact that certain metal atoms are required is itself evidence of the importance for catalysis of the electronic structure of metal atoms. The selectivity in consecutive reactions (hydrogenation of multiple unsaturated molecules) sometimes depends on the heat of adsorption of the starting molecules and intermediate products, and as heats of adsorption are usually only marginally affected by alloying, alloying does not change this kind of selective behavior of metals.

Catalysis by Alloys in Hydrocarbon Reactions

Introduction Evidence has accumulated in the last 20 years that spillover processes play a crucial role in many catalytic phenomena. Four symposia have highlighted the advances of knowledge in this area, and the progressive recognition that the phenomena have extremely important consequences (Delmon et al., 1973; Inui et al., 1993; Pajonk et al., 1983; Steinberg, 1989). In spite of this, very few kinetic models incorporating spillover have been presented. Little attention, if any, is given to these phenomena in the design of processes or in the definition of operating conditions. ∗Review based on a lecture presented at the 13th Colloquim on Chemical Reaction Engineering (13 CCRE), held in Windsor Castle, U.K., and jointly organized by the Working Parties “Chemical Reaction Engineering” and “Chemical Engineering in the Applications of Catalysis” of the European Federation of Chemical Engineering.

S.H. Inami

Papers

ESR evidence of hydrogen migration on supported metal catalysts

Olefin hydrogenation catalyzed by supported and unsupported mixed metals