## 3 Results and Discussion  
### Characterisation of the Fresh Catalysts  
XRD analysis was used to identify the crystal phases of the catalysts. The XRD patterns of the Ni/ZrO\({}_{2}\) and Co/ZrO\({}_{2}\) catalysts after reduction at 600 \({}^{\circ}\)C are displayed in Figure 2. The XRD spectrum was characterized by several intense peaks between the diffraction angles of 20\({}^{\circ}\) and 80\({}^{\circ}\). The XRD pattern of the Ni/ZrO\({}_{2}\) and Co/ZrO\({}_{2}\) catalysts contains Bragg peaks at around 20 = 44.52\({}^{\circ}\), which corresponds to metallic Ni. This can be attributed to the presence of the cubic [JCPDS 45-1027] structure of Ni and is in agreement with previous research [6; 35; 36; 37]. The diffraction peaks at 20 = 44.37\({}^{\circ}\) correspond to metallic Co [JCPDS 01-1254], similar to reports from previous works [38; 39]. It can be inferred that nickel oxide (NiO) and cobalt oxide (CoO) were reduced at 600 \({}^{\circ}\)C to metallic Ni [40; 41] and metallic Co [42], respectively. The relative intensity of XRD peaks of the supported catalysts depends on the nature of the metal oxide precursors formed during the calcination step [43]. The XRD patterns of the ZrO\({}_{2}\) support resulted in a number of peaks located at 20 of 24.47\({}^{\circ}\), 28.19\({}^{\circ}\), 31.48\({}^{\circ}\), 34.45\({}^{\circ}\), 40.73\({}^{\circ}\), 50.61\({}^{\circ}\), 55.62\({}^{\circ}\), 58.3\({}^{\circ}\), 60.02\({}^{\circ}\), 62.83\({}^{\circ}\), 69.67\({}^{\circ}\), and 71.29\({}^{\circ}\) corresponding to the (111), (200), (211), (300), (320), (400), (410), (411), (331), (332), and (422) crystal planes, which can be attributed to the monoclinic ZrO\({}_{2}\) (m-ZrO\({}_{2}\)) and tetragonal ZrO\({}_{2}\) (t-ZrO\({}_{2}\)) [JCPDS 83-0943] structure of the ZrO\({}_{2}\). This conforms with previous research [44; 45; 46; 47].  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Runs** & \(A\) (\({}^{\circ}\)C) & \(B\) (mL/min) & \(C\) (g) & \(D\) & \(E\) (wt \%) & **Phenol Conversion** & \(\mathbf{H_{2}}\) & **CO** & \(\mathbf{CO_{2}}\) \\ \hline
23 & 800 & 0.16 & 0.3 & 0 & 10 & 96.8 & 72.4 & 16.1 & 11.5 \\
24 & 800 & 0.46 & 0.1 & 1 & 2 & 9.7 & 25.2 & 7.4 & 67.4 \\
25 & 500 & 0.16 & 0.1 & 0 & 10 & 57.4 & 45.9 & 13.5 & 40.6 \\
26 & 500 & 0.16 & 0.3 & 0 & 10 & 58.1 & 51.5 & 14.8 & 33.7 \\
27 & 500 & 0.46 & 0.1 & 0 & 2 & 2.7 & 21.4 & 5.8 & 72.8 \\
28 & 500 & 0.46 & 0.3 & 1 & 2 & 5.7 & 22.4 & 6.2 & 71.4 \\
29 & 800 & 0.16 & 0.3 & 1 & 10 & 76.3 & 55.7 & 15.7 & 28.6 \\
30 & 800 & 0.46 & 0.3 & 0 & 10 & 77.9 & 56.8 & 15.8 & 27.4 \\
31 & 500 & 0.16 & 0.3 & 1 & 2 & 10.6 & 26.7 & 7.7 & 65.6 \\
32 & 800 & 0.46 & 0.3 & 0 & 2 & 19.5 & 30.1 & 9.7 & 60.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._  
Figure 2: XRD pattern for Ni/ZrO\({}_{2}\) and Co/ZrO\({}_{2}\) catalysts after reduction at 600 \({}^{\circ}\)C; (\(\bullet\)) peaks correspond to metallic Ni, (\(\blacksquare\)) peaks correspond to metallic Co, (\(\circ\)) peaks correspond to monoclinic phase of ZrO\({}_{2}\) (m-ZrO\({}_{2}\)) and (\(\circ\)) peaks correspond to tetragonal phase of ZrO\({}_{2}\) (t-ZrO\({}_{2}\)).  
To have better insights into the nature of the cobalt and nickel phases, TPR-H\({}_{2}\) of the calcined catalysts was carried out. This helped to explore the level of reduction of the Co and Ni oxides' species. Figure 3 shows that only single reduction zones were observed. This corresponds to the area below 400 \({}^{\circ}\)C (\(\sim\)280-450 \({}^{\circ}\)C), corresponding to the reduction of NiO [48; 49] and CoO [50; 51; 52] particles with weak metal-support interaction. Thus, the reduction of the NiO and CoO to metallic Ni and Co agrees with the XRD analysis. In particular, the reductions were peaks shifted to higher temperatures as the Co/ZrO\({}_{2}\) catalyst. This suggests that higher temperatures are needed in order to reduce the cobalt oxides (\(>\)452 \({}^{\circ}\)C) completely, as compared to nickel oxides [53]. Therefore, these catalysts were reduced at 600 \({}^{\circ}\)C.