## 3 Results
### Structural properties  
TEM images of the Au/MnO\({}_{2}\)-MF, Au/MnO\({}_{2}\)-NW and Au/MnO\({}_{2}\)-Comm materials obtained by this route are shown in Figure 1. The Au NPs deposited on the different supports were monodispersed, and had very small sizes of about 2.6 nm (\(\pm\)0.8 nm) in all cases. Moreover, as could be seen, Au nanoparticles were uniformly dispersed onto the MnO\({}_{2}\) surfaces. In addition, no significant agglomeration of gold nanoparticles was detected. Figure 1: TEM images of the Au/MnO\({}_{2}\)-NF catalysts (**B,C**), Au/MnO\({}_{2}\)-NW (**E,F**) and Au/MnO\({}_{2}\)-Comm (**H,I**) catalysts. Images (**A,D,G**) represent MnO\({}_{2}\)-NF, MnO\({}_{2}\)-NW and MnO\({}_{2}\)-Comm bare supports, respectively. Images (**C,H,I**) represent HAADF-STEM images. The different morphologies of the three different MnO\({}_{2}\) supports used were clearly observed in the TEM images. Moreover, significant differences were also observed in the specific surface areas of these materials, as can be seen in Table 1.  
The specific surface areas of both homemade MnO\({}_{2}\) supports (MnO\({}_{2}\)-NF and MnO\({}_{2}\)-NW) are roughly ten times as high as that of the commercial oxide (MnO\({}_{2}\)-Comm). The nanoflowers MnO\({}_{2}\) presented the highest surface, and also pore volume (Table 1). These characteristics could strongly influence the activity of this material. Moreover, the modification of the MnO\({}_{2}\) materials with gold nanoparticles did not change the structural and morphological properties of the bare support. Indeed, as could be expected, high dispersion of the gold nanoparticles permitted a slight increase in the overall specific surface areas of the prepared catalysts. It is interesting to note that the huge differences in the surface areas of the commercial support and the homemade samples did not impact the average particle size of the gold nanoparticles (Table 1). Indeed, this was one of the objectives of this work, and it is due to the method of preparation of the Au particles using PVP as a stabilizer. Taking into account the same average Au particle size and metal loading, it seems that the catalytic performances should be governed mostly by the structure and the morphology of the support. Interesting results were obtained from H\({}_{2}\)-TPR studies (Figure 2). The reducibility of the MnO\({}_{2}\) support represents an important parameter in the context of catalytic applications. This is because Au NPs (active phase) can strongly interact with metal oxides and change their redox properties. This, in turn, can affect catalytic activity. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Catalyst** & **Au (wt \%)** & **Particle size (nm)** & **Surface Area (m\({}^{2}\)/g)** & **Pore Volume (cm\({}^{3}\)/g)** & **Pore Diameter (Å)** \\ \hline Au/MnO\({}_{2}\)-NF & 1.3 & 2.6 & 196 & 0.42 & 6.1 \\ MnO\({}_{2}\) NF & - & - & 194 & 0.41 & 6.1 \\ Au/MnO\({}_{2}\)-NW & 1.3 & 3.2 & 125 & 0.16 & 6.9 \\ MnO\({}_{2}\)-NW & - & - & 122 & 0.16 & 6.8 \\ Au/MnO\({}_{2}\)-Comm & 1.4 & 2.6 & 15 & 0.05 & 17.8 \\ MnO\({}_{2}\)-Comm & - & - & 14 & 0.05 & 17.8 \\ \hline \end{tabular}
\end{table} 
Table 1: Au wt %, Au gold particle size, BET surface area, pore volume and pore diameter determined by FAAS, TEM and BET - N\({}_{2}\) adsorption, respectively. Figure 2: Temperature programmed reduction (TPR) profiles for MnO\({}_{2}\) nanoflowers (in blue), nanowires (in red), and commercial MnO\({}_{2}\) (in black) before and after the deposition of Au nanoparticles on their surfaces. The TPR profile for MnO\({}_{2}\) nanoflowers displayed two peaks, centred at 284 and 323 \({}^{\circ}\)C, assigned to the reduction of MnO\({}_{2}\) to Mn\({}_{x}\)O\({}_{y}\) (displaying lower oxidation states) [24]. After the deposition of the ultra-small Au NPs at the nanoflowers' surface, a marked change in the TPR profile was observed.