Deactivation of Hybrid Cobalt Catalyst Based on Hierarchical Porous Zeolite in Fischer–Tropsch Synthesis

Bifunctional Fischer–Tropsch synthesis catalysts open the way to more environmentally friendly technologies for producing a wide range of products, including motor fuels with desired properties in a single reactor. The development of new and improvement of existing catalysts is very important for the selective formation of fuel fractions. The use of bifunctional catalysts based on microporous zeolites is often accompanied by relatively rapid deactivation of acid sites, which leads to a decrease in the yield of fuel fractions and selectivity for branched hydrocarbons, thereby adversely affecting the octane number of gasoline and low-temperature characteristics of diesel fractions. One of the solutions to this problem is the use of zeolites with a hierarchical porous structure containing both micro- and mesopores. In the present work, a new hybrid catalyst for Fischer–Tropsch synthesis was synthesized based on a mixture of Co–Al2O3/SiO2 catalyst, HZSM-5 zeolite with a hierarchical porous structure, and boehmite. By forming pores of 2–8 nm size in the zeolite, an increase in the overall acidity of the zeolite and the number of Lewis acid centers due to its alkaline modification was achieved leading to an increase in the selectivity of the synthesis of hydrocarbons with a branched structure. By carrying out the long-term continuous tests for 2000 h of the synthesized hybrid catalyst, it was established that the rates of deactivation of the cobalt and zeolite components of the synthesized hybrid cobalt catalyst are comparable. The results of the physicochemical studies pointed out toward the agglomeration of cobalt particles and the formation of amorphous carbon as the primary reasons for the deactivation of the hybrid cobalt catalyst. The newly synthesized catalyst can be potentially used in modular units for producing motor fuels from natural and associated petroleum gases.