Elsevier

Applied Surface Science

Volume 257, Issue 19, 15 July 2011, Pages 8151-8164
Applied Surface Science

Review Article
Catalytic applications of amorphous alloys: Expectations, achievements, and disappointments

https://doi.org/10.1016/j.apsusc.2010.12.046Get rights and content

Abstract

This review intends to summarize the major achievements in the application of amorphous alloys as precursors of catalyst materials. This non-traditional catalyst preparation method may provide supported catalysts with novel chemical and structural properties. Selected examples for both glassy alloy precursors and those fabricated by mechanochemistry include CO oxidation over binary and ternary alloys, dehydrogenation over Cu–M (M = Ti, Zr or Hf), one-step synthesis of methyl isobutyl ketone, and selective hydrogenation of unsaturated carbonyl compounds. Ni alloys for methanation developed for the project to solve global warming by recycling carbon dioxide are also discussed.

Research highlights

► In situ activation of amorphous metallic alloy precursors. ► Characterization of formed materials by varied experimental techniques. ► Application of formed catalyst systems in organic transformations. ► High specific activities achieved in varied reactions.

Introduction

The development of the method in the early 1960s [1], [2], [3] to rapidly quench molten alloys to fabricate metallic alloys with glassy structures, also called amorphous alloys, glassy metals or metallic glasses, generated an upsurge of interest to study their physical and chemical properties. From the catalytic side their attractive properties are the lack of long-range order, non-porous nature, and the presence of the active species in a uniform dispersion in a chemically homogeneous environment.

During the three decades of the applications of amorphous alloys two major areas of interest have emerged: their use in the as-quenched state or as catalyst precursors. Since amorphous alloys are metastable materials structural relaxation and crystallization further enhanced by the adsorbed reactants resulting in surface reconstruction occur readily. As a result, intrinsic catalytic properties of amorphous surfaces have not yet been disclosed.

The use of amorphous alloys as catalyst precursors, in contrast, has been a successful research area. This non-traditional catalyst preparation method may provide supported catalysts with novel chemical and structural properties. It is not surprising, therefore, that the topic has been widely reviewed [4], [5], [6].

This review highlights major achievements with respect to the use of amorphous alloys as catalyst precursors through selected examples. Most examples discussed have been published by the author's group and include the use of glassy alloy precursors. Results with respect to the application of amorphous alloy powders fabricated by high-energy ball-milling also called mechanical alloying or mechanochemistry will also be covered. Reactions including CO oxidation, dehydrogenation of alcohols, the one-step synthesis of methyl isobutyl ketone, selective hydrogenation of unsaturated carbonyl compounds, and methanation as well as relevant catalyst characterization data acquired by varied experimental techniques are discussed.

Section snippets

Characterization of metallic glasses

The main characteristics of metallic glasses from the point of view of catalytic applications can be summarized as follows [4], [6].

The surface of amorphous materials, assuming the ideal case, has no long-range ordering of the constituents. In contrast, the surface is rich of low-coordination sites (terraces, steps, corner atoms) and defects. It is well-documented, that low-coordination sites play important roles in catalysis. Chemical composition of glassy metals is highly flexible. It allows

Catalytic applications of amorphous alloys

As discussed metallic glasses are thermodynamically metastable materials prone to structural changes. On the other hand, this property allows the study of the segregation behavior of alloy constituents under reaction conditions and their use as precursors of catalyst materials. Selected examples discussed below will highlight important achievements in the latter field.

Conclusions

Selected examples discussed and summarized in this review show that amorphous alloys fabricated by rapid quenching or high-energy ball-milling can serve as useful catalyst precursors in varied catalytic transformations. Appropriate characterization techniques revealed that various pretreatments and interaction with reagents during reactions induce significant physical and chemical changes. The outstanding performance (high activity, selectivity and stability) of the catalysts generated is

Acknowledgements

The author thanks students and colleagues for their valuable contribution to this research project over the years. Their names are to be found in the literature citations. Thanks are also due to Professors Imre Bertóti, Maria Janik-Czachor and Gabriele Mulas partners in a decade-long fruitful collaboration. Professor Koji Hashimoto is thanked for his initiation of collaboration, discussions and encouragement.

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