The effect of nonframework aluminum on acidity in dealuminated mordenite

Journal Article · Sat Oct 31 23:00:00 EST 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90011-6· OSTI ID:5602707

Miller, J T; Hopkins, P D ^[1]; Meyers, B L; Ray, G J; Roginski, R T; Zajac, G W; Rosenbaum, N H ^[2]

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1. Amoco Oil Co., Naperville, IL (United States)
2. Amoco Corp., Naperville, IL (United States)

Despite its high crystalline stability, mordenite (MOR) is relatively easily dealuminated. Calcination of NH[sub 4]-MOR to H-MOR at 500[degrees]C results in 20% dealumination with the production of octahedral, nonstructural aluminum located within the zeolite pores. The octahedral aluminum is nonacidic and does not affect the acid strength of the remaining structural aluminum ions. Calcination at 735[degrees]C results in over 50% dealumination, creating internal, nonacidic pentacoordinate aluminum. In H-MOR (735), 60% of the acid sites are equivalent in strength to H-MOR (500); however, the remaining acid sites are reduced in strength. Pentacoordinated aluminum may interact with the portion of structural aluminum: the aluminum is completely removed from the mordenite, leaving no nonframework species. Strong acid creates many SiOH defect sites; however, the SiOH defects did not affect the acid strength. High-temperature steam produces extensive dealumination. In the presence of steam, nonstructural aluminum migrates to the crystalline surface and restricts the pore aperture. Eventually, the pore aperture becomes sufficiently restricted that large molecules, e.g., n-hexane or pyridine, cannot diffuse to the zeolite interior. In steam-dealuminated mordenite, pentacoordinate aluminum also reduces the acid strength of 40% of the remaining acid sites. Qualitatively, the catalysts' activities for hexane cracking could be correctly ordered by either the number of strong acid sites (independent of the maximum acid strength) measured by NH[sub 3]TPD or infrared spectroscopy. 54 refs., 7 figs., 6 tabs.

• OSTI ID: 5602707
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 138:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTROSCOPY
ALKANES
AZINES
BROENSTED ACIDS
CALCINATION
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
CRACKING
DECOMPOSITION
DEFECTS
HETEROCYCLIC COMPOUNDS
HETEROGENEOUS CATALYSIS
HEXANE
HYDROCARBONS
HYDROGEN COMPOUNDS
ICP MASS SPECTROSCOPY
INORGANIC ACIDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MASS SPECTROSCOPY
MATERIALS
MINERALS
MOLECULAR STRUCTURE
MORDENITE
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PH VALUE
PYRIDINE
PYRIDINES
PYROLYSIS
SILICATE MINERALS
SPECTROSCOPY
THERMOCHEMICAL PROCESSES
ZEOLITES