Interplay between nanoscale reactivity and bulk performance of H-ZSM-5 catalysts during the methanol-to-hydrocarbons reaction

• Steaming leads to mesoporosity as well as to a decrease in acid site density and strength.
• Deactivation of H-ZSM-5 catalyst during MTH is governed by the formation of coke precursor species.
• Upon steaming changes in acidity are more pronounced in the external regions of the catalyst.
• STXM reveals a relation between coke precursor species and the distribution of acid sites.

H-ZSM-5 catalyst powders before and after a steaming post-treatment have been investigated during the Methanol-To-Hydrocarbons (MTH) process at 350 °C. Bulk and surface characterization techniques have been combined with in situ Scanning Transmission X-ray Microscopy (STXM) at the aluminum and carbon K-edge to study the changes in acidity, porosity, reactivity, and aluminum distribution upon steaming. It was found that steaming post-treatment has a positive impact on the stability of H-ZSM-5 without inducing important changes in the MTH activity and selectivity. The lower MTH stability of non-steamed H-ZSM-5 catalyst powder is related to the formation of poly-aromatic compounds in the outer regions of the catalyst particles, as probed with in situ STXM. In contrast, a limited amount of poly-aromatics was found in the outer rim of steamed H-ZSM-5 catalyst particles. These differences occur as a result of the generation of mesoporosity as well as the reduction in the number and strength of acid sites after steaming, as evidenced by the nanoscale imaging of adsorbed pyridine with STXM.

The reduced formation of poly-aromatic species in the outer regions of mildly steamed H-ZSM-5 zeolite powders leads to an improved methanol-to-hydrocarbons reaction stability.Figure optionsDownload high-quality image (62 K)Download as PowerPoint slide