Structure and density of active Zn species in Zn/H-ZSM5 propane aromatization catalysts

Journal Article · Thu Oct 01 04:00:00 EDT 1998 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1998.2177· OSTI ID:672467

Biscardi, J A; Iglesia, E ^[1]; Meitzner, G D ^[2]

---

1. Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering
2. Edge Analytical, Stanford, CA (United States)

Exchanged Zn cations increase propane conversion turnover rates, hydrogen formation rates, and selectivity to aromatics on H-ZSM5. In situ Zn K-edge X-ray absorption studies show that aqueous ion exchange with H-ZSM5 (Si/Al = 14.5) leads to isolated Zn{sup 2+} cations with tetrahedral symmetry. These Zn species reside at cation exchange sites as monomeric cations and form directly from nitrate solutions during ion exchange. X-ray absorption and temperature-programmed reduction studies show that Zn{sup 2+} cations in Zn/H-ZSM5 do not reduce to zero-valent species during propane reactions at 773 K. Extrazeolitic ZnO crystals form on samples prepared by impregnation techniques. In contrast to exchanges Zn{sup 2+} cations, these bulk ZnO crystals reduce to Zn metal and elute from the catalyst bed as Zn vapor under typical propane aromatization conditions. Condensation reactions of (Zn{sup 2+}OH){sup +} species with acidic OH groups appear to lead to the formation of the active Zn{sup 2+} cations interacting with two Al sites (O{sup {minus}}{single_bond}Zn{sup 2+}{single_bond}O{sup {minus}}). This active Zn species is supported by acid site density measurements from NH{sub 3} titration and isotopic titration of remaining Broensted acid sites with deuterium in Zn/H-ZSM5.

• Sponsoring Organization: National Science Foundation, Washington, DC (United States); California Univ., Berkeley, CA (United States); USDOE, Washington, DC (United States)
• DOE Contract Number: AC03-76SF00515
• OSTI ID: 672467
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 179; ISSN JCTLA5; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
36 MATERIALS SCIENCE
AROMATIZATION
CATALYTIC EFFECTS
CRYSTAL STRUCTURE
DEHYDROCYCLIZATION
POPULATION DENSITY
PROPANE
ZEOLITES
ZINC