Advanced Hydrodesulfurization Catalysts: A Review of Design and Synthesis

Proliferating energy consumption, particularly of fossil fuels, has led to an increasing generation of pollutants; many of these harmful products have been of serious environmental concern. While energy demand will continue to grow due to massive urbanization and industrialization, the ability to remove such pollutants has not yet been achieved. Therefore, policies are always being reviewed to accommodate the existing reality of minimizing the amount of pollutants released to the environment on a daily basis. Sulfur dioxide, a major environmental pollutant, gets to the environment through the combustion of sulfur-containing fuel in the engine of automobiles. Over the years, regulatory bodies such as the European Emission Standard have set limits to the amount of sulfur in transportation fuel to safeguard the environment. Lately, the limit for clean fuel specification with respect to sulfur content is set to nearly zero ppm. This policy came at a time when crude oil experienced a large decline in price, in addition to increased sulfur content and daily fluctuations of crude density. Compliance with this tight regulation will mean that refineries are expected to either modify their hydrotreating unit, which is capital intensive, or adopt robust catalysts, through research, that can work in tandem with the existing conventional hydrotreating catalysts to reduce the sulfur level to the required limit. This urgent demand has once more drawn the attention of the scientific community. Since there has been a great stock of research outcomes with respect to catalysts for hydrodesulfurization application in recent times, our aim is to collect and review those recent articles on hydrodesulfurization catalyst design and development. The tutorial review is therefore intended to cover a basic hydrodesulfurization overview, followed by detailed discussions on the recent development in the choice of active phases, their supports, and synthesis strategies. The work is expected to guide researchers, especially beginners that are interested in refinery hydrotreatment, on the recent development in hydrodesulfurization catalyst design and development.