## 1 Introduction  
Metal nanoparticles (MNPs) have received much attention for years due to their peculiar properties, which are appealing to basic sciences and innovative technologies. The complex interplay of several features provides them with unique electric, optical, magnetic, and chemical behaviors, which are determined by their composition, shape, and interaction with their local environment [1]. However, their high surface energy makes them unstable and highly reactive so that they easily oxidize and/or coalesce. To preserve their properties, their surface energy must be lowered; hence, the control of the preparation of MNPs is of the utmost importance to get reproducible materials. For this purpose, a wide range of chemical methods (bottom-up approach) is available, which generally require the aggregation of metal atoms obtained upon reduction under controlled conditions [2]. One way to stabilize MNPs against oxidation and/or coalescence is to use agents of both a molecular and macromolecular nature (capping agents and organic polymers, respectively) [3]. Among the latter ones, some have recently shown that gel-type cross-linked functional polymers (gel-type resins) are effective in the multi-gram scale preparation of MNPs [4]. In fact, on the basis of the nanometer size porosity of gel-type resins in the swollen state, we can control both the size and the size distribution of metal and metal oxide NPs through the template controlled synthesis (TCS) [5; 6; 7; 8], thus showing that TCS is a reliable method for the preparation of very small metal particles (\(<\)10 nm) entangled within the polymer framework. Most importantly, this framework, apart from providing an efficient and reliable size and dispersion control, stabilizes the MNPs against coalescence, oxidation, and early ageing while preserving a remarkable chemical activity [9]. As a matter of fact, resins proved to be useful scaffolds for the preparation of nanostructured inorganic phases both in catalysis and material science (see, for example, [10; 11; 12; 13; 14]) and the knowledge of their morphology is important in this respect [9; 15]. The great challenge in the frame of MNPs-based materials is the ability to understand and employ bimetallic systems in which the specific properties and characteristics of two different kinds of metals can be used and modulated. In several cases, bimetallic systems outperform the monometallic ones; however, very often, the specific reasons for this better behavior are not yet unequivocally understood [16; 17; 18]. In this regard, Au-Pd MNPs are exploited as catalysts for many reactions, such as, for example, the photoinduced generation of hydrogen molecules from water [19], oxidation of CO to CO\({}_{2}\)[20], hydrogenation reactions [21; 22], oxidation of alcohols and polyols with dioxygen [23], and direct synthesis of hydrogen peroxide (DS reaction) [24]. In several cases, Au-Pd catalysts perform better than monometallic Pd and their behavior has been widely investigated in the literature. It has been proposed that it is affected by the nature of the particles (alloys, eutectic-like, core-shell [25]) and several other experimental parameters, such as the synthetic procedure, and the composition and size of the MNPs [26; 27], but the complexity of these systems prevented a single explanation for their behaviors. In particular, bimetallic Au-Pd catalysts supported on gel-type resin are promising systems both for the oxidation of aliphatic alcohols [5] and for the DS reaction [14; 28; 29], but a general in-depth understanding of the beneficial effect of gold has not yet been achieved. The difficulty in the characterization of supported MNPs is multiple and arises from the presence of very small aggregates (usually less than 5 nm) embedded in an amorphous or crystalline matrix. The matrix, beneficial from the point of view of MNPs' stabilization and size/dispersion control, heavily complicates their characterization.