Recent advances in the unsupported catalysts for the hydrodesulfurization of fuel

With the increasingly prominent concerns on the environmental pollution from vehicles, the sulfur content in fuels must be limited to < 10 ppm around the world. The hydrodesulfurization (HDS) technology still is the dominant hydrorefining process of fuels. Traditional supported HDS catalysts usually refer to the Co(Ni)Mo/Al 2 O 3 with the shortages of low loading of active metals and strong metal-support interaction. Thus, the unsupported (or bulk) HDS catalysts without support have received increasing attention both from academia and industry in recent years. This review provides the research progress of unsupported catalysts for the HDS of fuel. Firstly, the overview of the HDS process was introduced, followed by the developments of template-free methods and template methods for preparing unsupported HDS catalysts. Finally, some crucial issues and the perspective of future development of unsupported HDS catalysts were summarized to achieve the goal of the production of ultra-low sulfur fuels. • The theory of the HDS process and the composition of unsupported catalysts were introduced. • The template-free and template methods for preparing unsupported HDS catalysts were summarized. • The analysis of structure-activity relationship over unsupported HDS catalysts was conducted.