Multitechnique characterization of dealuminated mordenites
Mordenite zeolites were altered both physically and catalytically by dry thermal treatments, acid leaching at mild temperatures, sequential thermal/acid treatments, and hydrothermal steaming. Good agreement was demonstrated between four diverse analytical procedures, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), /sup 29/Si and /sup 27/Al nuclear magnetic resonance (NMR), and NH/sub 3/ temperature-programmed desorption (TPD) and the extent of dealumination. Both XRD and NMR showed that dry heat treatments alone expelled as much as 70% of the aluminum from the framework of the fresh mordenite, but XPS showed no change in the surface aluminum concentration. Strong zeolite acidity as measured by TPD of NH/sub 3/ above 290/sup 0/C was nearly completely destroyed or made inaccessible by dry thermal treatment. This acidity was restored by acid leaching which removed the detrital aluminum, making the remaining tetrahedral aluminum sites accessible to NH/sub 3/. Roughly 40% of the remaining tetrahedral aluminum is lost from the structure upon steaming at 500/sup 0/C for 70 h. Here, XPS detects modest increases in surface aluminum concentration which were not observed for the heat-treated samples. This shows that steam is required for expelled aluminum to migrate to the zeolite surface. Acid dealumination of these mordenites was shown by N/sub 2/ adsorption to develop maximum micropore volume and to minimize external zeolite surface area. The changes observed do not fully explain the aging characteristics during methanol conversion exhibited by deeply dealuminated mordenites; however, changes in catalyst selectivity toward higher-molecular-weight products can be explained by increases in the micropore volume following acid dealumination.
- Research Organization:
- Amoco Research Center, Naperville, IL (USA)
- OSTI ID:
- 5287084
- Journal Information:
- J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 110:1; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020400 -- Petroleum-- Processing
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALCOHOLS
ALUMINIUM
ALUMINIUM 27
ALUMINIUM ISOTOPES
AMMONIA
AROMATICS
CATALYSTS
CATALYTIC CRACKING
CATALYTIC EFFECTS
CATALYTIC REFORMING
CHEMICAL PREPARATION
CHEMICAL PROPERTIES
CHEMICAL REACTIONS
COHERENT SCATTERING
CRACKING
CUMENE
DECOMPOSITION
DESORPTION
DIFFRACTION
DISSOLUTION
ELECTRON SPECTROSCOPY
ELEMENTS
EVEN-ODD NUCLEI
HEAT TREATMENTS
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOTOPES
LEACHING
LIGHT NUCLEI
MAGNETIC RESONANCE
MATERIALS
METALS
METHANOL
MINERALS
MORDENITE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUCLEAR MAGNETIC RESONANCE
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
PYROLYSIS
REFORMER PROCESSES
REMOVAL
RESONANCE
SCATTERING
SEPARATION PROCESSES
SILICATE MINERALS
SILICON 29
SILICON ISOTOPES
SPECTROSCOPY
STABLE ISOTOPES
STEAM
SYNTHESIS
THERMOCHEMICAL PROCESSES
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY
ZEOLITES