Dealumination of zeolites III. Effect of extra-framework aluminum species on the activity, selectivity, and stability of Y zeolites in n-heptane cracking
- Univ. de Poitiers (France)
A series of dealuminated Y samples with between 12 and 48 framework aluminum species per unit cell (N{sub Al}) were prepared by steaming of a NH{sub 4}NaY zeolite. A treatment with dilute HCl solution was applied to the samples in order to eliminate, without modifying the framework composition, the extra-framework aluminum species (EFAL) created by steaming. The activity, stability, and the selectivity in n-heptane cracking at 350 C of the two series of samples were compared. For high values of N{sub Al}, EFAL species have a promoting effect on the rates of isomerization, cracking, hydrogen transfer, and coking but increase the deactivating effect of coke. An inductive influence of their Lewis acid sites on the protonic sites of the zeolite (superacid sites) would be responsible for these effects. For N{sub Al} < 15 the reaction rates do not depend on the EFAL species probably because they are too far from the protonic sites. With all the reactions the activities of the dealuminated samples pass through a maximum for N{sub Al} between 35 and 40. The cracking activity of the highly dealuminated samples of the series containing few EFAL species is proportional to the number of the framework acid sites whereas for hydrogen transfer and for coking the activity depends also on the acid site density. This is attributed to the fact that these two reactions require many bimolecular steps and therefore demand the participation of several acid sites in their catalysis.
- OSTI ID:
- 5543232
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 130:2; ISSN 0021-9517; 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
ALKANES
ALUMINIUM
CARBONIZATION
CATALYSTS
CATALYTIC CRACKING
CATALYTIC EFFECTS
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COKING
CRACKING
DEACTIVATION
DECOMPOSITION
DEMETALLIZATION
ELEMENTS
HEPTANE
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGEN TRANSFER
INORGANIC ACIDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOMERIZATION
KINETICS
LEWIS ACIDS
MATERIALS
METALS
MINERALS
ORGANIC COMPOUNDS
PYROLYSIS
REACTION KINETICS
REMOVAL
SEPARATION PROCESSES
SILICATE MINERALS
STABILITY
STEAM
SURFACE PROPERTIES
SYNTHESIS
THERMOCHEMICAL PROCESSES
ZEOLITES