## 3 Nanocomposite Catalysts
### In Situ Synthesis Approach
Based on the detailed equilibrium studies, including analyses performed using Fourier-Transformation Infrared Spectroscopy (FT-IR) and X-Ray Powder Diffractograms (XRD) techniques, the appearance of Au and Pd micro- and nanostructures was not only confirmed but also linked with the changes of chemical structures of the anion exchange resins. A significant observation has been made that the reduction-coupled adsorption of Au(III), Pt(VI), and Pd(II) was followed by the decrease of pH of a solution and generation of oxygen in the mixture, indicating that the noble metals' ions indeed reduced in the structure of polymers [46; 47]. These, linked with the FT-IR spectra of the materials, recorded before and after reduction, allowed us to propose a mechanism that is displayed in Figure 5.  
Figure 4: Anion exchange resin (**A**) before and (**B**) after adsorption of Au(III). Figure reproduced from Reference [46], with the permission of Elsevier. Figure 5: Mechanism of reduction-coupled adsorption of Au(III) on amino-functionalized anion exchange resins. Figure reproduced from Reference [47], with permission of Elsevier. Based on the carried-out research, and a few of the literature reports [48], it was stated that the reduction of Au(III) began after excessive electron located on N atom transferred onto AuCl4-chlorocomplex. Then, observed changes of pH and O/O2 concentration suggested auto-oxidation of water molecules that generated electrons being able to regenerate amino functionality to reduce next AuCl4-. The process was very intensive, and the reduction was completed within a few hours, quantitively reducing Au(III). However, because of that, the resultant metallic Au and Pd were characterized by very wide distribution of their particles size, from nano- to micrometers. Moreover, larger particles were precipitated directly into the solution instead of the polymeric matrix, resulting in non-sufficient immobilization. Because reduction was carried out simultaneously with adsorption, it was concluded that the phenomenon was caused by the irregularities in concentration gradient at the solid-liquid interface. At the beginning of the reduction, the concentration gradient was high and decreased with time. As a result, more Au(III) was reduced. The solution for synthesizing Au, Pt, and PdNPs of defined granulometric properties was found, knowing the role of H2O in the reduction process. As displayed in Figure 6, the adsorption step was carried out in 1 mol L-1 HCl that suppressed the reduction [46; 49]. Then, the resins saturated with Au(III), Pt(VI), and Pd(II) were transferred to H2O, where the reduction began. Because the concentration gradient was defined by the number of moles of adsorbed Au, Pt, and Pd, it was possible to be controlled. As it was concluded, the greatest concentration gradient was observed near the surface of a resin's grain, while the smallest one was deep in the center thereof. Therefore, to obtain smallest in-size NPs, it was necessary to fully saturate a resin first. Then, reduction resulted in the fabrication of AuNPs from 4 to 21 nm in size. The smallest of them are displayed in Figure 7.  
Figure 6: Procedure for preparation of polymeric nanocomposites with noble metals’ nanoparticles. Figure reproduced from Reference [46], with permission from Elsevier. Figure 7: High-Resolution Transmission Electron Microscopy photomicrographs of AuNPs synthesized and stabilized in anion exchange resins. Figure reproduced from Reference [49], with permission from Elsevier. Within the carried-out research, a link between an applied amino functionality, acting as a molecular reactor, and the size and shape, as well as concentration, of Au, Pt, and PdNPs was found. Based on the results, it was stated that the smallest in-size NPs can be derived by using anion exchange resins bearing compounds revealing bis-amino functionality (such as 1,2-diaminoethane), while the greatest concentration thereof, was observed by applying amines of a heterocyclic nature [49].