Thermal Stability of Aluminum-Rich ZSM-5 Zeolites and Consequences on Aromatization Reactions

Abstract

The thermal stability and unique shape selectivity of the ZSM-5 structure have made this zeolite a popular choice for gas-phase petrochemical and biorenewable conversions. However, with processes such as catalytic fast pyrolysis and methane aromatization being studied at temperatures between 500 and 800 °C, it is imperative to better understand the dynamic changes that may occur under these conditions. Here, we study the chemistry of high aluminum content commercial ZSM-5 zeolites in the high-temperature regime. Our results suggest these catalysts thermally degrade within hours above 600 °C, emphasizing the importance of operating conditions on long-term catalyst performance. Detailed characterization of the thermally treated zeolites indicates that they retained the desired MFI crystallographic structure but displayed significant changes in Brønsted and Lewis acid site densities due to extensive dealumination. Depending on temperature, up to 50% of the aluminum initially present in the zeolite structure was lost to form extra-framework species that restrict the diffusion of reactants and products inside the catalyst particles. These alterations led to a 70% drop in performance for the catalyzed fast pyrolysis of cellulose. Low aluminum content ZSM-5 zeolites were more stable, suggesting a compromise must be found between reaction temperature and catalyst features to achieve high activity and long-term stability.

Spatial Confinement Effects of Microcapsule Catalyst for Improved Coking‐ and Sintering‐Resistant Behaviors Toward CO2 Reforming of Methane Reaction

“…However, the SiO 2 gives better sintering‐resistant property to coated catalysts by further restricting Ni particle mobility in relation to the supported catalysts. Although the mordenite framework inverted (MFI) structure for ZSM‐5 was maintained, a mild dealumination of the MFI structure was observed for all spent catalysts in the 2 θ range of 23°–25° which is in accordance with the reported literature . No diffraction peaks of SiO 2 were observed in all catalysts because SiO 2 remains amorphous.…”

Development of ZSM-22/Polyethersulfone Membrane for Effective Salt Rejection

“…Zeolites are alumina silicates materials widely used in ion exchanging, hydrocracking, adsorption and catalysis [42,43]. Recently, they have gained much consideration in the derivation of composite membrane materials owing to their external surface properties such as silinol, their negatively charged framework, shape selectivity and pore size exclusion [44][45][46][47]. These features promote high interaction between the polymer and additive as well with the solute cations and anions.…”

A strategy to convert propane to aromatics (BTX) using TiNp4 grafted at the periphery of ZSM-5 by surface organometallic chemistry

“…Most of the reported studies indicate that the yield of aromatics can be increased mainly by using a doping metal. [10][11][12] Several metals have been added to zeolites such as Ga, Mo, and Zn. The results indicate that Ga modified zeolites are the most efficient catalysts for light alkane aromatization.…”

“…The results indicate that Ga modified zeolites are the most efficient catalysts for light alkane aromatization. 10,[13][14][15][16] An industrial process has been successfully developed by BP and UOP and is known as the Cyclar™ process. 2,17 There is a consensus that Ga + is involved in the dehydrogenation step leading to olefins by an oxidative addition step and that the acid sites of zeolites facilitate catalysis, oligomerization, cyclization and aromatization steps.…”