# Nanosized Ni/SBA-15 Catalysts for CO\({}_{2}\) Reforming of CH\({}_{4}\)
## 3 Results and Discussion  
Table 1 summarizes the catalyst surface areas under investigation, measured using N\({}_{2}\) adsorption. The bare support, S15, had the highest surface area of 819.3 m\({}^{2}\)/g. The surface area loss on supporting Ni, Co, and Co-Ni with and without the modifiers was in the range of 33-35%. The results denote that the surface areas of all the catalysts were comparable, irrespective of the catalyst composition. The high surface area of the catalysts is attributed to the high area of the support, S15, as shown in Table 1.  
The XRD of the fresh calcined catalyst samples are displayed in Figure 1. The XRD pattern of the bare S15 carrier showed the amorphous nature of the mesoporous silica nanoparticles which is clearly in the 20 range of 20-30\({}^{\circ}\) (Figure 1a). Upon loading with 5 wt % Ni oxide (Figure 1b), the characteristic peaks matching to the (1 1 1), (2 0 0), and (2 2 0) planes of face-centered-cubic NiO appeared at 20 = 37.3, 43.3, and 62.9\({}^{\circ}\)[32; 33]. On the other hand, loading 5 wt % Co oxide into S15 (Figure 1c) produced peaks at 20 = 36.8, 44.8, 55.6, 59.4, and 65.2\({}^{\circ}\), corresponding to the (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), and (4 4 0) planes of the cubic phase of Co\({}_{3}\)O\({}_{4}\) spinel [33]. Upon doping with a mixture of 2.5 wt % of both Ni and Co oxide, characteristic peaks of Co and Ni oxide were detected, similar to what was observed with samples doped with Ce and Zn (Figure 1d,e, respectively). However, no characteristic peaks were observed for Ce and Zn as they might be highly dispersed, or the Ce and Zn species may have been included into the mesoporous framework of S15 [34]. The peak intensity of the modified supports is slightly higher compared to the non-modified, due to their being calcined two times. The catalysts were characterized using NH\({}_{3}\) desorption to examine the surface acidity of the prepared solids. Figure 2 illustrates the NH\({}_{3}\)-TPD profiles of the different catalysts. A major peak was observed at 100 \({}^{\circ}\)C for Co-Ni/S15, Co-Ni/Ce-S15, and Co-Ni/Zn-S15, and a minor peak was found at 100 \({}^{\circ}\)C for Ni/S15 and Co/S15. In the 260-350 \({}^{\circ}\)C range, minor peaks were detected for all catalysts. The two peaks observed for each catalyst in the range of 25-500 \({}^{\circ}\)C are attributed to the weak acidic sites. In the 600-700 \({}^{\circ}\)C range, peaks were detected for Co-Ni/S15, Co-Ni/Ce-S15, and Co-Ni/Zn-S15, which can be attributed to the strong acidic sites. The NH\({}_{3}\)-TPD profiles indicate that the modified support bimetallic catalysts showed stronger acidic sites compared to the non-modified samples. The acidic sites, especially the strong acidic sites, are expected to have a negative effect on CO\({}_{2}\) adsorption and to reduce the CO\({}_{2}\)/CH\({}_{4}\) conversion rate and the completion of CO\({}_{2}\) reforming of methane [7; 33; 35]. The lower CO\({}_{2}\) adsorption rate may facilitate other reaction pathways, thus reducing the catalyst selectivity. Overall, the NH\({}_{3}\)-TPD profiles suggest that the catalysts doped with Ce/Zn should exhibit lower activity than the non-doped catalyst. \begin{table}
\begin{tabular}{c c} \hline
**Catalyst** & **Surface Area (m\({}^{2}\)/g)** \\ \hline S15 & 819 \\ Ni/S15 & 547 \\ Co/S15 & 532 \\ Co–Ni/S15 & 549 \\ Co–Ni/Ce–S15 & 551 \\ Co–Ni/Zn–S15 & 548 \\ \hline \end{tabular}
\end{table} 
Table 1: Surface area of catalysts under study. Figure 3 shows the elucidated TPR profiles of the catalysts under study. The decreasing temperature is a sign of the presence of a certain species and indicates the degree of interaction with the support [35]. Two peaks were observed at 300 and 530 \({}^{\circ}\)C for Ni/S15, respectively, corresponding to two different  
Figure 1: XRD patterns of calcined samples: (a) S15, (b) 5% Ni/S15, (c) 5% Co/S15, (d) 2.5% Ni + 2.5% Co/Ce + S15, (e) 2.5% Ni + 2.5% Co/Zn + S15. Figure 2: NH\({}_{3}\) temperature-programmed desorption profiles of catalysts. NiO species.