ANS:A - Co-Mo

Cobalt-Molybdenum (Co-Mo) catalysts are widely used in the petroleum refining industry for various processes, including the desulfurization of naphtha. Here's an explanation of Co-Mo catalysts and their role in desulfurization:

1. Composition: Co-Mo catalysts consist of two main active components: cobalt (Co) and molybdenum (Mo). These elements are typically supported on a high-surface-area substrate, such as alumina (Al2O3) or silica-alumina, to increase the catalyst's surface area and maximize its catalytic activity.
2. Catalytic Activity: Co-Mo catalysts are effective in promoting the hydrodesulfurization (HDS) reaction, which is the primary mechanism for removing sulfur compounds from petroleum feedstocks such as naphtha. In the HDS process, sulfur-containing compounds present in the naphtha, such as thiols, sulfides, and thiophenes, undergo catalytic hydrodesulfurization to form hydrogen sulfide (H2S) and hydrocarbons. The Co-Mo catalyst facilitates this reaction by providing active sites for the adsorption and dissociation of sulfur compounds, as well as promoting hydrogenation reactions to remove sulfur atoms from the molecules.
3. Selective Desulfurization: Co-Mo catalysts are known for their selective desulfurization properties, meaning they can effectively remove sulfur compounds from the naphtha feedstock while minimizing undesirable side reactions, such as hydrocracking or hydrogenation of unsaturated hydrocarbons. This selectivity is crucial for maintaining the desired product quality and meeting regulatory specifications for sulfur content in gasoline and other refined petroleum products.
4. Regeneration: Co-Mo catalysts can undergo deactivation over time due to factors such as fouling by coke deposits or poisoning by contaminants in the feedstock. However, these catalysts are often designed for regeneration through processes such as thermal or chemical treatment to restore their catalytic activity and extend their operational lifespan.
5. Application: Co-Mo catalysts are used in fixed-bed reactors or trickle-bed reactors in industrial desulfurization units within petroleum refineries. These catalysts are typically employed in combination with hydrogen gas under elevated temperature and pressure conditions to maximize the efficiency of the desulfurization process.

Overall, Co-Mo catalysts play a vital role in the desulfurization of naphtha and other petroleum feedstocks, helping to produce cleaner-burning fuels with reduced sulfur content and meeting environmental regulations for emissions control. Their effectiveness, selectivity, and regenerability make them essential components of modern petroleum refining processes.