Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

Abstract

In order to elucidate phosphorus-zeolite H-ZSM-5 interactions, a variety of phosphorus-modified zeolite H-ZSM-5 materials were studied in a multi-spectroscopic manner. By deploying single pulse 27 Al, 31 P MAS NMR, 2D heteronuclear 27 Al-31 P correlation (HETCOR), 27 Al MQ MAS NMR spectroscopy, TPD of pyridine monitored by FT-IR spectroscopy, and Scanning Transmission X-ray Microscopy (STXM) the interplay and influence of acidity, thermal treatment and phosphorus on the structure and acidity of H-ZSM-5 were established. It was found that while acid treatment did not affect the zeolite structure, thermal treatment leads to the breaking of Si-OH-Al bonds, a decrease in the strong acid site number and the formation of terminal Al-OH groups. No extra-framework aluminium species was observed. Phosphorus precursors interact with the zeolitic framework through hydrogen bonds and physical coordination, as phosphorus species can be simply washed out with hot water. After phosphatation and thermal treatment two effects occur simultaneously, namely (i) phosphorus species transform into water insoluble condensed poly-phosphoric acid and (ii) phosphoric acid binds irreversibly to the terminal Al-OH groups of partially dislodged four-coordinated framework aluminium, forming local silico-aluminophosphate interfaces.These interfaces are potentially the promoters of hydrothermal stability in phosphated zeolite H-ZSM-5.

Phosphorous Modified ZSM-5 Zeolites: Impact on Methanol Conversion into Olefins

“…The presence of this shoulder has been ascribed previously to the fermi resonance of the m(OH) stretch with the 3d(OH) modes of bridging hydroxyls [27]. However, phosphanol groups (P-OH), usually vibrate in the 3200-3500 cm -1 region [18]. Though, their latter presence cannot be ascertained, the raise in the amount of Brønsted acid sites in ZSM-5FP with respect to pristine ZSM-5F (TPD measurements) might support the presence of such species.…”

“…In contrast, a post-modification of pristine zeolite with phosphoric acid led to a 30 % decrease in the number of Brønsted acid sites (entry 2). The effect of acid treatment during phosphatation has been recently shown to induce a decrease in the number of strong acid sites [18]. However, an increase in the number of weaker acid sites has also been observed by Lercher et al [19,20].…”

“…Indeed, HF was substituted by phosphoric acid which is not toxic and may induce the formation of P-containing ZSM-5 zeolite [16,17]. A double strategy was followed (Scheme 1) to prepare P-ZSM-5 zeolites: either via phosphoric acid addition directly in the synthesis gel, or by a post-treatment of the zeolite with phosphoric acid according to the literature [18][19][20].…”

Effect of Feedstock and Catalyst Impurities on the Methanol‐to‐Olefin Reaction over H‐SAPO‐34

“…Over time, great efforts have been made towards decreasing deactivation rates and increasing catalyst activity. Critical improvements have been made by modification of the catalyst crystal size and acidity; and an increased catalyst lifetime is reported for smaller crystal size and lower acidity 5, 6, 7, 8, 9, 10, 11…”

New micro and mesoporous materials for the reaction of methanol to olefins

“…The introduction of phosphorus to modify ZSM-5 is one of the ways to improve the propylene selectivity and reduce the aromatics product in the expense of the decrease of acidity [103][104][105][106], and with the washing of hot water, additional Brønsted acidity can be recovered [107,108]. Since it was firstly reported, the phosphorus modification of ZSM-5 has been applied to different reactions such as fluid catalytic cracking, toluene alkylation, and also methanol to hydrocarbons [108].…”