General Comments on Catalysis using Transition Metal Nanoparticles

General Comments on Catalysis using Transition Metal Nanoparticles 

During the last 2-3 decades a vast amount of knowledge regarding the preparation and characterization of nanostructured transition metal colloids in the zerovalent form has accumulated [1, 2]. The emphasis has been largely on the development of methods for the control of size and, more recently, even of shape [3]. In the majority of cases application in catalysis was not pursued systematically, i.e., generally only a simple model reaction such as the hydrogenation of cyclohexene was studied. 

Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim 

In contrast to nanoscaled transition metal colloids in the zerovalent form, less is known regarding the analogous metal oxides, i.e., colloidal MO (M=metal n= 1, 2, 3, etc.). Of course, such species in solid bulk form or as immobilizates on surfaces or in solid carriers have been known for a long time in heterogeneous catalysis [4], in semiconductor technology and other areas [3, 5]. More recently special methods have been developed for their preparation in constrained environments [6], in microemulsions [7], or as one- or two-dimensional nanostructures [5d, 8]. 

This chapter focuses mainly on the author s own contributions in the area of aqueous nanoscaled transition metal oxides. Specifically, the preparation in high concentration and application of aqueous colloids comprising metal oxide and mixed metal oxide nanopartides will be described. The chapter begins with a short overview of the author s earlier work on methods for size- and shape-selective preparation of transition metal (zerovalent) colloids, because this led to the development of simple and practical ways to prepare the corresponding aqueous transition metal oxide coUoids. 

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