Review on Hydrodesulfurization over Zeolite-Based Catalysts

Abstract

Concerning the environmental and health problems related to SO x emission, the environmental protection agencies are incessantly tightening the permissible sulfur level in fuels such as gasoline and diesel. This gives a greater challenge for the traditional hydrodesulfurization (HDS), which is quite inefficient for removing refractory sulfur (RS) compounds (e.g., 4,6-dimethyldibenzothiophene). Consequently, the new efficient HDS catalysts for substituting the industrial HDS catalysts (Ni­(Co)­Mo/Al2O3) have received much attention. Zeolite-containing HDS catalysts are of particular importance because zeolites could alleviate the HDS of RS compounds via isomerization and cracking abilities of their Brønsted acid sites. The microporous zeolites slow down the diffusion of reactants and products, leading to uncontrolled cracking reactions that promote the coke formation and thus deactivate the HDS catalysts. Therefore, the application of zeolite-based catalysts was limited for HDS reactions in the early years. But, due to the introduction of hierarchical porous structure in zeolites, the cracking reactions catalyzed by strong Brønsted acid sites are controlled and uninterrupted molecular diffusion becomes highly possible. As a sequel, a better selectivity and improved HDS efficiency are attainable without any coke formation or with a reduced coke formation. Besides the porosity and acidity of zeolites, the synthetic methods and precursors of zeolite-based HDS catalysts and the mixing of zeolites with other supports like Al2O3 have impacts on the efficiency of zeolite-based HDS catalysts. In this review, all these factors are discussed along with the preparation methods of hierarchical zeolites and tuning methods of zeolite acidity. The process and catalyst details of traditional HDS are briefly explained at the outset. The types of metal active component present in various zeolite-based HDS catalysts and how their properties are influenced by zeolites are also summarized.

A 3D Extra-Large Pore Zeolite Enabled by 1D-to-3D Topotactic Condensation of a Chain Silicate

“…The uses of zeolites (1)(2)(3)(4) are limited by the size of their pores, so zeolites with larger pores are in demand (5). Natural and synthetic zeolites possess a fully connected three-dimensional network of corner-sharing SiO 4 tetrahedra (i.e.…”

“…1C). At the edge of the ZEO-2 chain, four silanols/silanolates form a single four-member ring (S4R) that faces, slightly displaced, an identical S4R from the next chain, with hydrogen bonding along the [110] and [1][2][3][4][5][6][7][8][9][10] directions providing connection between adjacent chains (Fig. 1B).…”

A 3D Extra-Large Pore Zeolite Enabled by 1D-to-3D Topotactic Condensation of a Chain Silicate

“…The uses of zeolites (1)(2)(3)(4) are limited by the size of their pores, so zeolites with larger pores are in demand (5). Natural and synthetic zeolites possess a fully connected three-dimensional network of corner-sharing SiO4 tetrahedra (i.e.…”

Porous liquids – the future is looking emptier

“…Microporous materials have widespread applications in gas capture, 1,2 molecular separations, 3,4 catalysis, 5,6 and energy storage. [7][8][9] Traditionally, these materials have been solid, but recently, permanent porosity has been translated into the liquid state.…”