## 2 Fundamentals of Heterogeneous Catalysis
In 1813, [PERSON] discovered that ammonia decomposes into nitrogen and hydrogen when passed over various burning metals. In 1823, [PERSON] found that the activity of different metals such as iron, copper, silver, gold, and platinum for decomposing ammonia decreased in that order. Meanwhile, in 1814, [PERSON] reported that acids facilitate the hydrolysis of starch to glucose. In 1817, [PERSON] and [PERSON] noted hydrogen oxidation by air over platinum, and [PERSON] studied why platinum facilitates oxidation reactions [41; 42]. With these initial researchers, heterogeneous catalysis evolved into a crucial aspect of the chemical industry. This is because catalysts, usually solid, are at a different phase than reactants and products, thereby making their separation more cost-effective. Key characteristics of an effective catalyst include activity, selectivity, reproducibility, thermal and mechanical stability, and ease of regeneration. Additionally, catalyst activity is influenced by the nature, quantity, strength, and spatial arrangement of the chemical bonds formed temporarily between the reactants and the catalyst surface, which depends on the solid catalyst's composition, structure, and morphology [35; 43]. As we know, the catalyst activity is highly dependent on the active component(s) included in its surface structure and composition. In the specific case of heterogeneous catalysis, catalyst activity is composed of a main active component, the proportion of which exceeds that of other components and secondary components, which are included to improve the catalyst's activity, called additives or, sometimes, promoters or modifiers. The promoter is a substance that does not have catalytic properties by itself; however, when added to the catalyst, it improves its properties, for instance, by stabilizing the catalyst structure or by modifying the chemical properties of the catalyst surface [35; 44]. Heterogeneous systems offer several advantages compared to conventional homogeneous catalysis, such as the following:Solid catalysts can be easily separated from the reaction products, and this is very important, allowing the recovery of the catalyst for future reuse in the reaction medium; Separation simplifies and reduces product purification washing steps; In the same way that the volume of water for washing and purifying the organic phase is reduced, it is a very important advantage from an environmental point of view due to reduced wastewater discharges; The possibility of using raw materials of lower quality and consequently lower cost. Recent advancements in heterogeneous catalysis have focused on increasing efficiency, selectivity, and durability. Tailored synthesis of ceramic materials facilitates the creation of catalysts with optimized properties. Additionally, sustainable and green catalysis is an emerging area, aiming to create environmentally friendly catalytic processes that reduce waste and energy consumption [45; 46]. Heterogeneous catalysts are crucial in many industrial applications, such as the production of high-purity biodiesel and glycerol [47; 48], degradation of environmental contaminants [49], and catalytic support [50], among many other uses. [PERSON] [39] categorizes heterogeneous catalysts into seven groups: metal oxides, mixed and doped metal oxides, supported catalysts, zeolites, lamellar double hydroxides, organic bases, and anionic resins. Supported catalysts, which disperse active catalytic materials onto high surface area solid supports, are of great industrial interest [51]. These supports are chosen for their porosity, mechanical resistance, and ability to prevent active metal particle sintering, which can be catalytically active or inactive [52]. Nanometric metal particles dispersed on these supports (such as alumina, silica, and/or zeolites) enhance catalytic efficiency, reduce costs through lower metal usage, offer adjustable selectivity, and enable catalyst reuse [53].