Insights into coke location of catalyst deactivation during in-situ catalytic reforming of lignite pyrolysis volatiles over cobalt-modified zeolites

Simultaneous Enhancement of Aromatic Products and Catalytic Lifetime for Catalytic Re-forming of Lignite Pyrolysis Volatiles over a Self-Assembled Hierarchical Core–Shell ZSM-5@Silicalite-1 Zeolite

“…However, the newly formed thin silicalite-1 shell can passivate part of the surface acid sites of the zeolite, thus inhibiting the occurrence of polymerization reactions, which generate coke species on the outer surface of the catalyst. In addition, the reduced content of BAS is also responsible for inhibiting the formation of coke species, which has been demonstrated in a previous report . On the basis of the above discussion, a proposed location of coke formation over the core–shell zeolite and over the conversional ZSM-5 zeolite during the upgrading of lignite pyrolysis volatiles to produce BTEXN is presented in Scheme .…”

“…In addition, the reduced content of BAS is also responsible for inhibiting the formation of coke species, which has been demonstrated in a previous report. 8 On the basis of the above discussion, a proposed location of coke formation over the core−shell zeolite and over the conversional ZSM-5 zeolite during the upgrading of lignite Scheme 1. Fabrication Mechanism of the Hierarchical Core−Shell of ZSM-5@Silicalite-1 Using TPAOH and TEAOH Solutions for Different Hydrothermal Times ) (Figure 8).…”

“…However, for the catalytic re-forming of lignite volatiles, mass transfer limitations will reduce the access of the large molecular components to the active sites, resulting in a low utilization efficiency and a rapid formation of coke precursors. 8,9 On the one hand, the narrow channels in the conventional ZSM-5 zeolite confine the diffusion of reactants and coke precursors, leading to secondary reactions and rapid deactivation. On the other hand, both the strong Brønsted acid site (BAS) generated by the framework aluminum and the Lewis acid site (LAS) formed by external surface acid sites also accelerate the rate of coke formation by polycondensation of macromolecular compounds.…”

“…In situ catalytic re-forming of lignite pyrolysis volatiles to light aromatics has been proven to be a promising alternative method to enrich light aromatics, such as benzene (B), toluene (T), ethylbenzene (E), xylene (X), naphthalene (N), and methylnaphthalene (MN) products. , It is well-known that the pore structure and acidity of a zeolite, such as Y, ZSM-22, Al/SBA-15, and ZSM-5 can significantly control the composition and distribution of light aromatic products. − Among these diverse zeolites employed in the catalytic re-forming of lignite pyrolysis volatiles, ZSM-5 is considered to be the most promising candidate for the catalytic upgrading pyrolysis of biomass/coal tar because of its high hydrothermal stability, tunable acid sites, and well-defined shape selectivity to BTEXN. However, for the catalytic re-forming of lignite volatiles, mass transfer limitations will reduce the access of the large molecular components to the active sites, resulting in a low utilization efficiency and a rapid formation of coke precursors. , On the one hand, the narrow channels in the conventional ZSM-5 zeolite confine the diffusion of reactants and coke precursors, leading to secondary reactions and rapid deactivation. On the other hand, both the strong Brønsted acid site (BAS) generated by the framework aluminum and the Lewis acid site (LAS) formed by external surface acid sites also accelerate the rate of coke formation by polycondensation of macromolecular compounds. , Therefore, designing a zeolite with abundant mesopore pores and appropriate acid distribution and concentration will improve the conversion of lignite to light aromatics by catalytic re-forming reactions.…”

Formation of Light Aromatics and Coke during Catalytic Reforming of Biopolymer-Derived Volatiles over HZSM-5

“…The pore size distribution as shown in Figure a also suggested the increased porosity in SHZSM-5-C. A low coking tendency was observed for SHZSM-5-L, although the same HZSM-5 was used for the upgrading of the volatiles. The pore accessibility of the spent catalysts was much more than that of the fresh ones, which revealed that the coke growth caused the aggregation of the deposited species on the surface of the catalyst, as concluded by other works. , A great variety can be observed for the deposited species as the coke precursors on the spent HZSM-5 because the biomass structure in terms of the three components has great differences. In addition, Jia et al indicated that the coke growth is associated with a high acidity of HZSM-5.…”