## 2 Results and Discussion  
Two Au-Pd catalysts (P50: 2% Au: 2% Pd, _w/w_--1:1.85, mol/mol; P75: 3% Au: 3% Pd, _w/w_--1:5.57, mol/mol) were prepared with a two-step procedure (see Supporting Information) [5; 7]. With the very same procedure, we also prepared two Au and Pd monometallic specimens. The total Au-Pd weight fraction was set to 4% for both the bimetallic samples and to 3% for the monometallic ones. The metal content of the samples was calculated from the difference of the metal concentration in the metal solution before and after the metal uptake. These bimetallic materials were employed as catalysts in the DS reaction, under non-explosive, relatively mild conditions, without the addition of any selectivity enhancer (such as mineral acids and halide ions) [40]. Although the catalytic productivity was low, this ensures that the observed performance of the catalysts depends exclusively on their intrinsic properties. The productivity of P50 and P75 materials was 109 and 97 mmol\({}_{\rm H_{2}O_{2}}\)/mol\({}_{\rm H_{2}}\), respectively, better than a related monometallic Pd catalyst whose productivity was 64 mmol\({}_{\rm H_{2}O_{2}}\)/mol\({}_{\rm H_{2}}\). A-XRD measurements were performed at the BM08 beamline of the ESRF facility (Grenoble, France) [41] using an angle-dispersed set-up [42], based on a large area imaging plate detector (200 \(\times\) 100 mm\({}^{2}\)), which ensured high quality/high statistics XRD patterns [33]. Glass capillaries (diameter 0.5 mm) were used as specimen holders for the powdered P50 and P75 samples. During the collection of the data, specimens were kept under rotation and continuously flushed with N\({}_{2}\) to prevent any oxidation of the metal phases. The XRD patterns I\({}_{\mathrm{N}}\) and I\({}_{\mathrm{F}}\) were collected tuning the X-ray beam near (E\({}_{\mathrm{N}}\)\({}^{\mathrm{Au}}\) = 11,910 eV, E\({}_{\mathrm{N}}\)\({}^{\mathrm{Pd}}\) = 24,345 eV) and far (E\({}_{\mathrm{F}}\)\({}^{\mathrm{Au}}\) = 11,700 eV, E\({}_{\mathrm{F}}\)\({}^{\mathrm{Pd}}\) = 24,001 eV) from the Au L\({}_{\mathrm{III}}\) (E\({}_{\mathrm{Au}}\) = 11,919 eV) and Pd K (E\({}_{\mathrm{Pd}}\) = 24,350 eV) edges. The size distribution and morphology of the MNPs in P50 and P75 were preliminary characterized by TEM and high resolution (transmission) electron microscopy (HREM). TEM images of P50 and P75 specimens (see Supporting Information and Figure S1) revealed a bimodal size distribution (Figure 1) with small (d \(\sim\) 1-2 nm) and a few medium size (10-20 nm) particles, the latter being larger in the P75 sample. All the observed MNPs have the same crystalline fcc lattice, but the mismatch among the Au, Pd, and Au-Pd lattices is so small that TEM measurements did not provide any reliable information about the MNPs' phase composition (JCPDS card No 04-0784). Figure 2 shows the A-XRD patterns collected at the Au L\({}_{\mathrm{III}}\) edge and Pd K edge, panels (a) and (b), respectively, as a function of the energy independent abscissa, s = sin(\(\theta\))/\(\lambda\), for the two specimens P50 and P75. They show an intense background scattering coming from the polymer matrix and well defined peaks due to the MNPs. The abscissa values of the most intense peaks, calculated assuming a lattice parameter for Au a\({}_{\mathrm{Au}}\) = 4.079 A (JCPDS card No 46-1043), are in good agreement with the ones of pure Au (Figure 2a,b). The broad halo observable between the Au (111) and Au (200) lines is especially evident in the difference patterns, \(\Delta\)I = I\({}_{\mathrm{F}}\) - I\({}_{\mathrm{N}}\) (Figure 2, panels c and d), where the contribution of the polymer matrix was subtracted. Since the difference pattern obtained from the A-XRD is due only to  
Figure 1: Particle size distribution of P50 and P75 specimens. Very small nanoparticles (1–2 nm) and a few large clusters are present in both the specimens.