## 1 Introduction  
Cerium oxide or ceria (CeO\({}_{2}\)) is considered one of the most promising metal oxides for numerous catalytic applications, such as catalytic oxidation of CO [1; 2; 3], NO reduction [4; 5; 6], water-gas shift reaction [7; 8; 9; 10], reforming reactions [11; 12] and soot combustion [13; 14; 15]. In particular, CeO\({}_{2}\) has attracted extensive interest due to its abundant oxygen vacancies, interchangeability between Ce\({}^{3+}\) and Ce\({}^{4+}\) oxidation states and high oxygen storage capacity (OSC) [16; 17; 18]. During the past few decades, nanotechnology has made remarkable progress toward the development of ceria nanocomposites with distinct physical and chemical properties, greatly expanding their potential applications in energy and environmental catalysis [19; 20]. In this perspective, we recently showed that among ceria nanocomposites of different shape, ceria nanorods possess enhanced reducibility that is linked to their high population in intrinsic defects and oxygen vacancies. The latter is considered responsible for their superior CO oxidation performance [21].  
More importantly, ceria-based mixed oxides have recently gained increasing attention in the fields of materials science and heterogeneous catalysis, due to their unique surface, structural and electronic properties, which are completely different to those of parent counterparts. The combination of various transition metals with CeO\({}_{2}\) nanoparticles leads to enhanced surface and redox properties due to the \"synergistic\" interactions between the oxide phases. Accordingly, various CeO\({}_{2}\)-based transition metals (M/CeO\({}_{2}\), M = Mn, Fe, Co, Ni, Cu) have been widely employed in heterogeneous catalysis [22; 23].  
Among the different transition metal oxides, zinc oxide (ZnO) is a wide and direct band gap semiconductor, which has been used in many fields, due to its low cost and environmental sustainability [24; 25; 26]. Zinc is not a critical raw material, thus no direct impact on the environmental resources is considered. Moreover, it is abundant in the steel industry as one of the main recovered products in the metal scrap recycling process [27]. In view of this fact, the potential of a low-cost metal, able to further enhance the catalytic performance of CeO\({}_{2}\), is of particular importance both from an environmental and economic point of view.  
Although CeO\({}_{2}\)-ZnO composites have been extensively used in photocatalysis [28; 29; 30; 31; 32], only a few studies have been devoted to their catalytic applications. [PERSON] et al. [33] reported on the enhanced CO oxidation activity of CeO\({}_{2}\)-ZnO composites, which is ascribed to the synergistic interaction between ZnO hollow microspheres and commercial CeO\({}_{2}\) powders. In a similar manner, the synergistic interaction between ZnO and CeO\({}_{2}\) is considered responsible for the enhanced CO oxidation performance of three-dimensional ordered macroporous CeO\({}_{2}\)-ZnO [34].  
In light of the above aspects, the present work aims for a first time at investigating the impact of ZnO as modifier for ceria nanorods (NR), in an attempt to further adjusting their surface/redox properties. To this end, a series of pure CeO\({}_{2}\) and ZnO along with CeO\({}_{2}\)/ZnO mixed oxides of different Zn:Ce atomic ratios (0.2, 0.4, 0.6) were prepared by the hydrothermal method. The as-prepared materials were thoroughly characterized by X-ray diffraction (XRD), N\({}_{2}\) adsorption at -196 \({}^{\circ}\)C (Brunauer-Emmett-Teller (BET) method), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM) and H\({}_{2}\) temperature-programmed reduction (H\({}_{2}\)-TPR). The oxidation of CO was used as a probe reaction to disclose structure-activity relationships.