Hexane Cracking over Steamed Phosphated Zeolite H‐ZSM‐5: Promotional Effect on Catalyst Performance and Stability

Abstract

The nature behind the promotional effect of phosphorus on the catalytic performance and hydrothermal stability of zeolite H-ZSM-5 has been studied using a combination of (27) Al and (31) P MAS NMR spectroscopy, soft X-ray absorption tomography and n-hexane catalytic cracking, complemented with NH3 temperature-programmed desorption and N2 physisorption. Phosphated H-ZSM-5 retains more acid sites and catalytic cracking activity after steam treatment than its non-phosphated counterpart, while the selectivity towards propylene is improved. It was established that the stabilization effect is twofold. First, the local framework silico-aluminophosphate (SAPO) interfaces, which form after phosphatation, are not affected by steam and hold aluminum atoms fixed in the zeolite lattice, preserving the pore structure of zeolite H-ZSM-5. Second, the four-coordinate framework aluminum can be forced into a reversible sixfold coordination by phosphate. These species remain stationary in the framework under hydrothermal conditions as well. Removal of physically coordinated phosphate after steam-treatment leads to an increase in the number of strong acid sites and increased catalytic activity. We propose that the improved selectivity towards propylene during catalytic cracking can be attributed to local SAPO interfaces located at channel intersections, where they act as impediments in the formation of bulky carbenium ions and therefore suppress the bimolecular cracking mechanism.

Aluminum-Phosphate Binder Formation in Zeolites as Probed with X-ray Absorption Microscopy

“…Also, Zhuang et al obtained similar results for phosphated H-ZSM-5 after a steam treatment (800 °C, 10 h). It is interesting how this relates to the well-known promotional effect of phosphorus on the hydrothermal stability H-ZSM-5, but beyond the scope of this work 17,71,76. In the case of H-ferrierite, due to the inaccessible nature of the {Al} EF species, the formation of a crystalline AlPO 4 phase is unlikely to take place.…”

Probing the Location and Speciation of Elements in Zeolites with Correlated Atom Probe Tomography and Scanning Transmission X‐Ray Microscopy

“…[20,21] Both APT and STXM have been applied to zeolite-based catalysts by a number of research groups, resulting in a significant body of accumulated knowledge. [20,[24][25][26][27][28][29][30][31][32][33][34] However, to the best of our knowledge, there are no reports that correlate results of the two characterization techniques. Herein, we have applied APT and STXM in an integrated fashion to study the same single crystal of a laboratory aged (135,000 mile simulation) sample of copper-exchanged zeolite SSZ-13 (Cu-SSZ-13, CHA framework topology), which is the same sample as we previously studied with APT alone.…”

Visualizing Dealumination of a Single Zeolite Domain in a Real‐Life Catalytic Cracking Particle

“…[14,15] In order to understand zeolite activity in the context of FCC catalysis,w here matrix and binder materials play ak ey role,characterization techniques that possess both spatial and chemical information are required. [24][25][26][27][28] Here,wepresent afirst-of-its-kind study in which we used STXM to probe zeolite dealumination within real-life fresh and genuine,industrially deactivated FCC catalysts at the size regime of asingle zeolite domain. 10-30 nm) spatial resolution.…”