**6. Conclusion**

*Nanocatalysts*

**Table 1.**

size resulting in a high number of potential catalytic sites [37]. Owing to these phenomena, there has been in the past two decades an increase in the use of metal nanoparticles in catalysis [38, 39]. Rong et al., reported the synthesis of supported Pt NPs and their use as catalysts in the partial hydrogenation of nitroarenes to arylhydroxylamines [40]. The particles were prepared by reduction of H2PtCl6 with NaBH4 in the presence of the carbon support. The hydrogenation of several substituted nitroarenes was performed under soft conditions (10.15°C, 1 bar H2) to favor the formation of hydroxylamines, showing excellent activity and selectivity in this transformation. Pd supported on C has also been successfully used as catalysts for

*Hydrogenations performed using Pt/C as catalysts (Catal. Sci. Technol., 2014, 2445, Ref. [39]).*

The proposed mechanism for the hydrogenation of nitrobenzene was proposed as shown in **Figure 8**. During this process, there is generation of intermediates such

For example, in the case of m-dinitrobenzene, a catalyst containing 2 wt% Pt/C yielded 92.3% of the corresponding hydroxylamine after 190 min of reaction in

In a study, Zeming et al. used carbon as Pt colloid support for the hydrogenation of arylhydroxylamines. The Pt colloid supported on carbon was an active and selective catalyst for the partial hydrogenation of nitroaromatics with electronwithdrawing substituents to the corresponding N-arylhydroxylamine, indicating an additive-free green catalytic approach for arylhydroxylamine synthesis. Very encouraging results were obtained with N-arylhydroxylamine bearing electronwithdrawing substituents. Since N-arylhydroxylamine can be further converted to highly valuable compounds through several reactions like Bamberger rearrangement, this result will generally contribute to a simpler and greener synthetic

Progress has been reported in the application of nano-PGMs for heterogeneous catalysis reactions. While most of the applications have centered on organic transformations, there is potential for extending the catalytic potential of these metals to other fields such as pollutant degradation and microbial inactivation in water

the conversion of nitrobenzenes to secondary amines (**Figure 7**).

as hydroxylamines, azo and azoxy derivatives.

methodology of N-arylhydroxylamine derivatives.

THF (**Table 1**).

**5. Future perspectives**

**50**

Several efforts have been devoted to the preparation of PGM nanocatalysts for application in environment decontamination. The high number of literature reports highlights the interest in this family of catalysts for catalytic transformation, both in terms of reactivity and selectivity. There is potential for application of PGMs nanocatalysts for environmental decontamination, water treatment, antimicrobial and chemical transformation. Further studies are necessary to better understand parameters influencing the reactivity as well as enhancing the conversion rates and efficiencies.

## **Acknowledgements**

Appreciation towards funding received from the University of South Africa (UNISA), the National Research Fund (NRF) and support from the Nanotechnology and Water Sustainability and Research Unit (NanoWS) is highly expressed.

## **Conflict of interest**

The authors declare that there is no conflict of interests concerning the publication of this book chapter.
