Abstract
Zeolite SAPO-34 has been widely used in the industry because of its special pore structure and wide distribution of acid sites in the pore channel. However, traditional SAPO-34 with a small pore size suffers from carbon deposition and deactivation in catalytic reactions, and its inability to catalytically convert bulky organic molecules limits its industrial application. Meanwhile, impurities of SAPO-5, which have weak acidity leading to rapid catalyst deactivation, appear in SAPO-34 zeolite. Therefore, it is of great significance to synthesize SAPO-34 zeolite with a mesoporous pore structure, which can significantly improve the transfer of molecules in zeolites. In this paper, SAPO-34 zeolite with a hierarchical pore structure was synthesized, and its hydrodesulfurization performance for 4,6-dimethyldibenzothiophene (4,6-DMDBT) was studied in a fixed bed reactor. The characteristic results show that BET-specific surface area, micropore volume, and mesoporous volume of synthesized SAPO-34 are 754 m2 g−1, 0.25, and 0.23 cm3 g−1 respectively, and the pore size is mainly concentrated at 4 nm. The catalytic conversion of 4,6-DMDMT with Co- and Mo-supported SAPO-34 is about 83%, which is much higher than the catalytic performance of Al2O3.
Highlights
Aluminophosphate (AlPO) zeolite is composed of alternating AlO4 and PO4 tetrahedrons (Wilson et al, 1982), and has no Bronsted acidity due to the absence of exchangeable electric charge in its framework
Fu Ye et al studied SAPO-34 prepared with different silicon and aluminum sources and found that the zeolite synthesized with inorganic silicon and aluminum sources has the highest crystallinity, while the zeolite synthesized with organic silicon and aluminum sources has the lowest crystallinity, and the effect of silicon source on crystallinity is smaller than that of the aluminum source (Fu et al, 2001)
The better crystallization condition is 200°C–48 h (SAPO-34-M13). Given all of those above, the conditions for synthesizing SAPO-34 zeolite with a mesoporous structure are as follows: silica sol and pseudo boehmite are used as inorganic silicon and aluminum sources, phosphoric acid is used as phosphorus source, DEA is used as microporous template, and organosilane DM3010 is used as mesoporous structure directing agent (SDA)
Summary
Aluminophosphate (AlPO) zeolite is composed of alternating AlO4 and PO4 tetrahedrons (Wilson et al, 1982), and has no Bronsted acidity due to the absence of exchangeable electric charge in its framework. Traditional SAPO-34 has a small pore size and is prone to carbon deposition and deactivation in catalytic reaction of bulky organic molecules, which cannot meet the needs of the development of the chemical industry (Zhong et al, 2017; Kim et al, 2021; Zhang et al, 2021) To cope with these shortcomings, several strategies have been developed to improve the diffusion limitation of SAPO-34, such as synthesis of nano-sized mesopore-containing SAPO-34 (Yang et al, 2014; Sun et al, 2018; Mi et al, 2021). Hierarchical porous SAPO34 was synthesized by using diethylamine (DEA) and morpholine as SDA, silicone quaternary ammonium salt {[(C2H5O)3SiC3H6N+(CH3)2C18H37]Br} as mesoporous SDA, and phosphoric acid, pseudo boehmite, and silica sol as phosphorus source, aluminum source, and silicon source, respectively. Γ-Al2O3 was used as the catalyst support for the same catalytic reaction
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