Preparation of metal/zeolite catalysts: Formation of palladium aquocomplexes in the precursor of palladium-mordenite catalysts
Previous research has revealed that the catalytic performance of metal/zeolite catalysts can be significantly modified by exposing the catalyst precursor to H[sub 2]O vapor during the period after calcination, but before reduction. For bimetallic PdCo/NaY catalysts used for CO hydrogenation, the selectivity was changed from predominant production of oxygenates to predominant production of higher hydrocarbons. For Pt/H-mordenite catalysts, this water treatment has been reported to improve the alkane isomerization activity. Although it is certain that Lewis sites are transformed to Bronsted sites by reaction with H[sub 2]O, the activity of the catalyst is affected most when the water is added after calcination, when the noble metal is present as ligand-free ions. This observation led to the hypothesis that complexation of transition metal ions with water might be instrumental for the observed effects. In zeolites containing cages, such as Y, the formation of metal-ligand complex ions appears to incite their migration from small to large cages. In cageless zeolites such as mordenite, however, it is not clear, a priori, whether hydration of transition metal ions will increase or decrease their reducibility and whether it will ultimately result in higher or lower metal dispersion. The authors have therefore undertaken research to clarify these issues. Palladium supported in H-mordenite (Pd/HMor) or Na-mordenite (Pd/Na-Mor) has been tested using methylcyclopentane as a probe reaction; temperature-programmed reduction (TPR), desorption (TPD), and extended X-ray absorption fine structure (EXAFS) spectroscopy have been used to characterize the effects of water treatment on the samples.
- OSTI ID:
- 5738295
- Journal Information:
- Journal of Catalysis; (United States), Vol. 143:1; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
02 PETROLEUM
MORDENITE
CATALYTIC EFFECTS
CHEMICAL PREPARATION
PALLADIUM COMPLEXES
ABSORPTION SPECTROSCOPY
CATALYST SUPPORTS
CATALYSTS
CYCLOALKANES
DESORPTION
HETEROGENEOUS CATALYSIS
PALLADIUM
REDUCTION
TEMPERATURE DEPENDENCE
X-RAY SPECTROSCOPY
ALKANES
CATALYSIS
CHEMICAL REACTIONS
COMPLEXES
ELEMENTS
HYDROCARBONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MATERIALS
METALS
MINERALS
ORGANIC COMPOUNDS
PLATINUM METALS
SILICATE MINERALS
SORPTION
SPECTROSCOPY
SYNTHESIS
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENTS
ZEOLITES
400201* - Chemical & Physicochemical Properties
020400 - Petroleum- Processing