## 1 Introduction  
Catalysis has gained ongoing attention from academic and industrial community, since it is massively involved in numerous energy and environmental processes, including, among others, the manufacture of value-added fuels and chemicals, hydrocarbons processing, fuel cell applications, photocatalytic degradation, abatement of hazardous substances, etc. To this end, the development of cost-efficient catalysts with improved activity and durability constitutes the main research pillar in the field of catalysis [1; 2; 3; 4; 5; 6; 7; 8]. Although, noble metals (NMs) hold an integral role in catalysis for chemical bond activation and formation, their scarcity and high cost constitutes a major and inherent drawback. In this regard, the development of catalysts by combining the low cost with the high activity is a major driving force in contemporary research [2; 3; 4; 5; 6; 8; 9; 10]. In this regard, however, a critical question arises: Is it feasible to adjust the surface chemistry of earth-abundant but relatively inactive materials in order to exhibit similar or ever superior performance to that of NMs? On account to the enormous progress so far accomplished on nano-synthesis, surface/interface functionalization and catalyst promotion fields, the answer to this question is definitely yes, as recently demonstrated [11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. Metal oxides, composed of earth-abundant transition metals (TMs) have gained particular attention towards replacing the rare and costly NMs, owing to their unique characteristics, such as improved redox properties and thermal stability [2; 3; 5; 6; 9; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46]. More importantly, through admixing different metal oxides (MOs) in an exact proportion, mixed metal oxides (MMOs) can be obtained with unique physicochemical properties, which are mainly linked to interfacial phenomena. In particular, MOs-based transition metals have received particular attention due to the distinctive chemisorption ability of TMs, related to their partially filled d-shells [47; 48]. Moreover, several reducible oxides (e.g., CeO\({}_{2}\), ZnO, and TiO\({}_{2}\)), could serve as TMs supporting carriers, exerting a beneficial impact on the inherent activity through peculiar metal-support interactions [49; 50; 51; 52; 53; 54; 16; 25; 54; 16; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46]. Among the different MOs, cerium oxide or ceria has gained tremendous interest in heterogeneous catalysis due to its exceptional redox properties driven by the high oxygen mobility and the rapid redox interplay between Ce\({}^{3+}\) and Ce\({}^{4+}\)[2; 9; 21; 23; 55; 56; 57]. In addition to these physicochemical advantages of cerium oxide, its average 2020 price stands at very low levels (ca. 1815 USD/metric ton), with a relative cost trend of ZrO\({}_{2}>\) ZnO \(>\) SiO\({}_{2}>\) TiO\({}_{2}>\) CeO\({}_{2}\), revealing the economic benefits of ceria-based catalytic materials [58]. Furthermore, the cost of base middle-late 3d metals, such as Cu, Ni, is about 3 to 4 orders of magnitude lower as compared to NMs, rendering extremely attractive, from a financial perspective, the development of ceria-based transition metal catalysts. More importantly, the combination of reducible oxides (e.g., CeO\({}_{2}\)) with TMs (e.g., Fe, Co, Ni, and Cu) could offer novel catalyst formulations with exceptional properties, arising mainly from the multifaceted electronic and geometric interactions amongst the different counterparts [49; 50; 51; 52; 53; 54; 16; 25; 55; 56; 14; 14; 15; 59; 60].