# Influence of CeO\({}_{2}\) Addition to Ni-Cu/HZSM-5 Catalysts on Hydrodeoxygenation of Bio-Oil
## 3 Results and Discussion
### Characterization of Catalysts
#### 3.2.6 Xps  
XPS was used to characterize the electronic state and distribution of elements on the surface of the catalysts. By comparing the XPS spectra of the 15% CeO\({}_{2}\)-Ni-Cu/HZSM-5 catalyst before and after the reaction, the change in the valence state of cerium before and after the reaction can be analyzed. Furthermore, by comparing the XPS spectra of different catalysts under the same reaction conditions, the morphology and distribution of the carbon deposited on the surface of the catalyst can be effectively analyzed. The binding energies near the peaks shown in Figures 8 and 9 were directly retrieved from the instrument. The XPS analyses for the catalyst before and after HDO exhibited peaks in the vicinity of  
Figure 7: The H\({}_{2}\)-Temperature-Programmed Reaction (TPR) profiles of catalysts with different CeO\({}_{2}\) contents. 884.5 and 905.4 eV (Figure 8a), which corresponded to the electron bonding energy of Ce3d\({}_{5/2}\) and Ce3d\({}_{3/2}\), respectively [24]. The electronic binding energy of 920.6 eV (Figure 8a) belongs to the position peak of Ce\({}^{4+}\)[25]. Figure 8b shows that the binding energy of Ce in the catalyst after the reaction exhibits approximately more than 2.5 eV of chemical shift of the Ce3d peaks, indicating a change in the valence state of Ce in the strong reduction atmosphere. According to the standard XPS spectra of Ce, the peak of Ce3d\({}_{5/2}\) (887.9 eV) in the catalyst before the reaction is attributable to CeO\({}_{2}\), whereas the peak of Ce3d\({}_{5/2}\) after the reaction (885.1 eV) is attributable to the low-valence Ce, indicating that the Ce\({}^{4+}\) content of the catalyst is reduced to Ce\({}^{3+}\) during the reaction. In addition, part of the Ce\({}^{4+}\) in CeO\({}_{2}\) is reduced to Ce\({}^{3+}\), oxygen vacancies are produced, and free electrons and lattice oxygen are released. The released electrons can be transferred to the active site of Ni\({}^{0}\), thereby adjusting the electronic state of Ni atom on the surface, improving the interaction between the carrier and the active component resulting in better dispersion of Ni [26; 27], and thus improving the catalyst's redox ability. The release of lattice oxygen is also beneficial in transferring active carbon species on the catalyst surface, thus promoting coke removal [27; 28]. Figure 8: The Ce3d XPS spectra of 15%CeO–Ni–Cu/HZSM-5 before (**a**) and after (**b**) the reaction. Figure 9: The Ni 2p XPS spectra of the deactivation catalyst after the reaction at 270 \({}^{\circ}\)C for 1 h.  
Figure 9 shows the Ni 2p XPS spectra of the used catalyst after the reaction at 270 \({}^{\circ}\)C for 1 h. The electron binding energies of Ni 2p in the Ni-based catalyst were approximately 856.5, 862, and 870 eV, corresponding to the Ni-O bond, the shakeup peaks, and the Ni\({}^{0}\) of the reduced state, respectively [29]. As seen from Figure 9, the peaks (865-869 eV) near 870 eV (Ni\({}^{0}\) of the reduced state) is the lowest in the catalyst without adding CeO\({}_{2}\), and correspondingly, the 856 eV peak (Ni-O) was relatively the highest. Thus, a small part of Ni\({}^{0}\) was translated into the Ni-O bond with the CeO\({}_{2}\) added catalysts resulting in a small amount of nickel oxidized, eventually leading to enhanced hydrogenolysis. In other words, the virgin catalyst limits the HDO reaction, and the catalyst becomes more conducive to carbon deposition [30]. The Ni\({}^{0}\) content in the catalyst with CeO\({}_{2}\) addition is higher than that without CeO\({}_{2}\), and a slightly negative shift in the electron bonding energy is observed, which proves that the addition of CeO\({}_{2}\) can increase the electron density of Ni\({}^{0}\), increase the electronegativity of Ni, and improve the reduction ability of Ni [30]. Moreover, the Ni\({}^{0}\) content and the electron binding energy of the catalysts with different CeO\({}_{2}\) contents were also significantly different.