Preface

Nanocatalysis is a topical area of research that has huge potential. It attempts to merge the advantages of heterogeneous and homogeneous catalysis. The collection of articles in this book treats the topics of specificity, activity, reusability, and stability of the catalyst and presents a compilation of articles that focuses on different aspects of these issues. Thus, the first chapter of the book introduces and overviews the present status of understanding in the area of nanocatalysis. The tailoring of nanostructures to combine aspects of catalysis requires understanding of the mechanisms involved. For instance, the influence of size and shape of nanoparticles on their catalytic properties is specific to a particular reaction. Multimetallic nanoparticles provide an additional variety for inducing reaction-specific catalyst properties. Another chapter illustrates the successful use of zirconia nanoparticles as catalysts for the multicomponent reaction of isatin derivatives with ammonium acetate and aromatic aldehydes under solvent-free conditions. The authors emphasize the reusability and stability of these zirconia nanocatalysts for this class of reactions, and review the catalytic properties of functionalized and core–shell-type iron oxide-based magnetic nanoparticles. The chapter focuses on the effect of different types of functionalization on their catalyst properties for specific organic reactions. Platinum group-based nanoparticles are one of the most studied classes of catalysts applied to different types of reactions. This book includes a chapter emphasizing the use of such catalysts to facilitate reactions needed for environmental remediation. Another chapter talks about the nanomaterials that have been successfully used as catalysts for the preparation of compounds needed in composite solid propellants. Given the diversity of nanostructures and their applications treated here, we believe that this book will be an active source of information for research in the field of nanocatalysis.

> **Editor Dr. Indrajit Sinha** Department of Chemistry, Indian Institute of Technology (BHU), Varanasi, India

**Co-editor Dr. Madhulata Shukla** Department of Chemistry, G. B. College, Ramgarh, Veer Kunwar Singh University, India

**1**

**Chapter 1**

**1. Introduction**

oxidation, etc. [3].

mance of the catalyst.

Introductory Chapter: Salient

*Alkadevi Verma, Madhulata Shukla and Indrajit Sinha*

Drawbacks in homogeneous and heterogeneous catalysts necessitate new catalytic paradigms for overcoming the limitations associated with both types. The model catalyst should combine the advantages of homogeneous with heterogeneous catalysis. Thus, the catalyst for a particular reaction should exhibit good activity, selectivity, and product yield. At the same time, it should be separable (recoverable) from the reaction medium, stable and reusable. Tailored nanostructures have

Transition metals, specifically precious noble metals such as Pt, Pd, Rh, Ru, Au, Ag, and Cu, are commonly used as homogeneous and heterogeneous catalysts in majority of chemical transformations [1, 2]. The primary reason for this is the variable oxidation states offered by them. They also possess good adsorption properties essential for heterogeneous catalysis. Combination of these two properties enables the transition metal nanoparticles to act as electron conduits for the reactants adsorbed on the surface of the catalyst. Initial examples of nanoparticles in catalysis were Ag nanoparticles in photography and Pt utilized in the decomposition of hydrogen peroxide (H2O2). Thereafter, noble metal nanoparticles have been used extensively as catalysts for many organic reactions such as carbon-carbon coupling in Suzuki, Stille and Heck reactions, hydrogenation, dehydrogenation reaction,

Nanoparticles, owing to high surface energies, tend to get agglomerated resulting in enhanced particle sizes with lower surface area. The latter implies lesser number of surface active sites in the catalyst. Stabilizers such as surfactants or polymers, that may also act functionalizing agents, are frequently used to protect nanoparticles surfaces against aggregation. Such surface altering processes also cause change in the electronic structure of the nanoparticle and because of that in their catalytic activity as well [4]. The other approach to circumvent this problem is by implanting these NPs on large surface area but low density insoluble solids supports like zeolites, carbon based materials etc. The support material may be relatively inert. Alternatively, the support could modify the chemical and adsorption properties of the catalyst. Active supports like these may enhance of impede the performance of the catalyst for a specific reaction by tuning the electron density of NPs. Another possible scenario is that the support is a better adsorbent for one of the reactants and thereby improves the perfor-

Currently, nanoparticles are increasingly substituting conventional heterogeneous catalysts [5]. Due to smaller sizes, nanoparticles have higher surface area and increased exposed active sites. In that way nanoparticles have larger contact areas with reactants and are catalytically more active than conventional heterogeneous catalysts. Variations in shape and composition of nanocatalysts give access to

Features of Nanocatalysis

displayed the potential to meet these stringent requirements.

### **Chapter 1**
