Acid strength of silica-supported oxide catalysts studied by microcalorimetric measurements of pyridine adsorption

Journal Article · Fri Feb 01 00:00:00 EST 1991 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(91)90193-8· OSTI ID:5485940

Cardona-Martinez, N; Dumesic, J A ^[1]

---

1. Univ. of Wisconsin, Madison (USA)

Microcalorimetric measurements of the differential heat of pyridine adsorption were used to probe the distribution of acid strength on a series of silica-supported oxide catalysts. Depositing oxides of the following cations onto silica increased the acid strength of the catalyst: Ga{sup 3{plus}}, Zn{sup 2{plus}}, Al{sup 3{plus}}, Fe{sup 3{plus}}, Fe{sup 2{plus}}, Mg{sup 2{plus}}, and Sc{sup 3{plus}}. The acid strength distribution curves for the supported oxide samples showed either two or three regions of constant heat of adsorption while silica had an energetically homogeneous surface. The Ga, Al, and Sc samples were found to have both Bronsted and Lewis acidity while the remaining samples showed only Lewis acidity. Incremental adsorption of pyridine indicated that the initial region of highest heat corresponds to strong Lewis acidity while intermediate heats seemed to be due to weaker Lewis acid sites or a combination of Lewis and Bronsted acid sites. The final region of lowest heat was due to H-bonded pyridine on silica. Estimates of the entropies of adsorption were determined, providing information about the mobility of the adsorbed pyridine molecules. The initial differential heat of adsorption increases proportionally to the Sanderson electronegativity of the added oxide.

• DOE Contract Number: FG02-84ER13183
• OSTI ID: 5485940
• Journal Information: Journal of Catalysis; (USA), Vol. 127:2; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
02 PETROLEUM
CATALYSTS
PH VALUE
PYRIDINE
ADSORPTION
ADSORPTION HEAT
ALUMINIUM OXIDES
BROENSTED ACIDS
CALORIMETRY
CATALYST SUPPORTS
CATALYTIC EFFECTS
ENTROPY
GALLIUM OXIDES
IRON OXIDES
LEWIS ACIDS
MAGNESIUM OXIDES
SCANDIUM OXIDES
SILICON OXIDES
ZINC OXIDES
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
AZINES
CHALCOGENIDES
ENTHALPY
GALLIUM COMPOUNDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
IRON COMPOUNDS
MAGNESIUM COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PYRIDINES
SCANDIUM COMPOUNDS
SILICON COMPOUNDS
SORPTION
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
ZINC COMPOUNDS
400201* - Chemical & Physicochemical Properties
020400 - Petroleum- Processing