## 3 Results and Discussion  
### Characterization of the Cu/SiO\({}_{2}\) Catalysts  
Table 1 summarizes the CuNP particle sizes obtained by the different protocols and final metal loadings on the silica supports before and after the catalytic test, determined by ICP-AES. Quantitatively similar metal loadings were observed, for the fresh and used catalysts, confirming the absence of leaching phenomena under catalytic testing conditions. Figures S1 and S2 in Supplementary Materials show both TEM micrographs and histograms of the size distribution of copper nanoparticles before impregnation onto the silica. The CuCTAB/SiO\({}_{2}\) presented a turquoise-blue final color, while the CuOB/SiO\({}_{2}\) and CuAsc/SiO\({}_{2}\) resulted in brown solids (Figure S3 in Supplementary Materials). The specific surface area and the N\({}_{2}\) adsorption isotherms of the fresh and used materials are detailed in Table 2 and Figure 3, respectively. Both CuOB/SiO\({}_{2}\) and CuCTAB/SiO\({}_{2}\) displayed an approximate decrease in specific surface area of 15%, with 12% losses observed for CuAsc/SiO\({}_{2}\). Consequently, the thermal process conducted during the catalytic tests did not significantly affect textural properties of the catalysts. This surface area reduction could be associated with partial sintering and intergrowth of a fraction of the spent CuAsc/SiO\({}_{2}\) catalyst, corroborated by STEM-EDX analysis  
DSC results (Figure S4 in the Supplementary Materials) showed that the organic components present in the CuNP suspensions (CuAsc and CuCTAB) were completely decomposed at the selected calcination temperature of 500 \({}^{\circ}\)C. X-ray diffraction analysis (Figure 4) of the calcined CuOB/SiO\({}_{2}\) catalyst revealed a CuO monoclinic structure of tenorite (2\(\theta\): 35.6\({}^{\circ}\) (111) and 38.7\({}^{\circ}\) (111) JCPDS 5-0661). In contrast, the same sample used under H\({}_{2}\)-SCR NO\({}_{\mathrm{X}}\) reaction conditions showed the presence of metallic particles of Cu\({}^{0}\) (20: 43\({}^{\circ}\) (111) JCPDS 4-0836), thereby indicating that copper species remain reduced after being under reaction. Raman spectra (Figure S5, in Supplementary Materials) further confirmed that CuO species were present in both fresh and used catalysts due to the presence of Cu-O features at 300 and 350 cm\({}^{-1}\)[37; 38]. The XRD pattern of the calcined CuAsc/SiO\({}_{2}\) catalyst pointed out the presence of CuO moieties. However, after reaction, no copper species signals were distinguished in the corresponding diffractogram, but CuO could be observed by Raman spectroscopy. This could be due to the presence of particle sized smaller than the DRX instrument limit detection or that the species were amorphous \begin{table}
\begin{tabular}{c c c c} \hline \hline
**CuNPs** & **Size (nm) 1** & **Catalyst** & **Cu Loading (\%) 2** & **Cu Loading (\%) 2** \\  & & & **Fresh Catalyst** & **Used Catalyst** \\ \hline CuO & - & CuOB/SiO\({}_{2}\) & 0.7 \(\pm\) 0.1 & 0.7 \(\pm\) 0.1 \\ CuAsc & 3.3 \(\pm\) 0.9 & CuAsc/SiO\({}_{2}\) & 0.9 \(\pm\) 0.1 & 0.9 \(\pm\) 0.1 \\ CuCTAB & 2.4 \(\pm\) 0.7 & CuCTAB/SiO\({}_{2}\) & 0.5 \(\pm\) 0.1 & 0.5 \(\pm\) 0.1 \\ \hline \hline \end{tabular} 1  
\end{table} 
Table 1: Particle size of the as prepared CuNPs and final Cu loading on the fresh and used catalysts. or atomically dispersed on the support [39]. No DRX patterns of copper species were detected for either fresh or used CuCTAB/SiO\({}_{2}\) catalysts. Nevertheless, CuO species could still be detected by Raman spectroscopy on the after-reaction sample (bands located at ca. 300 and 350 cm\({}^{-1}\) in Figure S5 in Supplementary Materials) [40]. The fresh sample CuAsc/SiO\({}_{2}\) (not shown) also exhibited fluorescence under Raman measurement conditions [41]. Figure 4: X-ray diffractograms of fresh and used catalysts. Figure 3: Nitrogen adsorption isotherms of the fresh and used catalysts.