# Influence of CeO\({}_{2}\) Addition to Ni-Cu/HZSM-5 Catalysts on Hydrodeoxygenation of Bio-Oil
## 1 Introduction  
Biomass is one of the most promising renewable energy sources for supplementing traditional fossil fuels; at present, biomass energy accounts for 10-14% of the world's energy supply [1]. A promising method for producing alternative fuel is to convert biomass into bio-oil. However, bio-oil composition is complex, its chemical properties are unstable, and it requires further modification and upgrades to become a high-quality liquid fuel. Presently, one of the most effective means of upgrading is the catalytic hydrogenation of bio-oil, in which catalyst selection plays a key role. In recent years, increasing attention has been paid to Ni-based catalysts with a relatively high activity. [PERSON] et al. [2] prepared a series of catalysts by loading Ni onto molecular sieves (HZSM-5 and Al\({}_{2}\)O\({}_{3}\)). Phenol was selected as a model compound to observe the hydrogenation activity of the catalysts. Their results showed that when the Ni loading was 10 wt% and the reaction temperature was 240 \({}^{\circ}\)C, the activity of the catalyst was the highest and the conversion efficiency of phenol reachedthe highest value (91.8%). [PERSON] et al. [3] used the impregnation method to load different Ni contents on the mixed carriers of Al\({}_{2}\)O\({}_{3}\)-SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\)-TiO\({}_{2}\), TiO\({}_{2}\)-SiO\({}_{2}\), and TiO\({}_{2}\)-ZrO\({}_{2}\). The catalyst was tested in reaction with guaiacum, a model compound of bio-oil. The experimental results showed that Ni/TiO\({}_{2}\)-ZrO\({}_{2}\) catalysts exhibited a better hydrodeoxygenation (HDO) activity. The conversion of bio-oil was 19.3%, the pH changed from 2.4 to 4.2, and the water content decreased remarkably from 51.4% to 1.5%. In addition, the Ni-Cu bimetallic catalyst was prepared by considering the advantages and disadvantages of various catalysts. The experimental results also showed that the HDO effect of the Ni-Cu bimetallic catalyst was significantly improved. [PERSON] and [PERSON] [4] loaded Cu onto Ni metal (with hydrogen atoms) and applied the temperature-rising desorption method for catalyst characterization. They found that the hydrogen atoms adsorbed on Ni metal overflowed onto the surface of the Cu atoms, which provided a new idea for the design of catalysts. In particular, a small amount of active metals (i.e., Cu) was added to the transition metals (i.e., Ni) to produce Ni-Cu alloys, which not only improved the dispersion of the active metal Ni but also reduced the binding energy between the active metals and the hydrogen atom. The method allowed the activated hydrogen to easily be desorbed from the catalyst surface and to enter the reaction system, thus effectively improving the hydrogenation activity of the catalyst. A small amount of Cu can serve as hydrogen storage, and it can also decrease the reduction temperature of the metal, thereby laying a foundation for the preparation of an anti-coke catalyst in the hydrogenation and deoxidation of bio-oil. [PERSON] et al. [5] prepared a series of bimetallic catalysts by impregnating different Ni-Cu contents onto \(\delta\)-Al\({}_{2}\)O\({}_{3}\), in which the total metal content was 20 wt%. The effects of different catalysts on bio-oil HDO were studied in the Ni/Cu mass ratio range of 0.32-8.1. Their results showed that the content of aliphatic hydrocarbons in the products of Ni-Cu bimetallic catalysts was significantly higher than that of single-metal Ni catalysts. When the Ni/Cu ratio reached 8, the yield of the oil phase was 40%, the oxygen removal efficiency was 57%, and the hydrogen consumption of the catalyst was the highest. The catalytic activity was optimal in the process of bio-oil catalytic hydrogenation. However, although Ni-Cu-based catalysts can significantly improve the HDO of bio-oil, the coke deposition on the catalysts remains a difficult problem. Coke deposition is the main cause of catalyst deactivation [6; 7; 8; 9; 10].