Molybdenum-oxo species deposited on alumina by adsorption. III. Advances in the mechanism of Mo[sup (VI)] deposition

Journal Article · Sun May 01 04:00:00 EDT 1994 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1994.1114· OSTI ID:7288132

Spanos, N; Lycourghiotis, A ^[1]

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1. Univ. Campus, Patras (Greece)

It was established that both the adsorption of Mo[sub 7]O[sup 6[minus]][sub 24] and MoO[sup 2[minus]][sub 4] ions and the deposition of MoO[sup 2[minus]][sub 4] ions by surface reaction with two neutral hydroxyls of the support take place, but the contribution of each of these processes depends on the impregnating conditions. Specifically, in the pH range 8.5-6.1 the deposition practically occurs through the reaction of MoO[sup 2[minus]][sub 4] ions with neutral surface hydroxyls of the support resulting in the formation of the surface complex Al[sub 2]O[sub 3]MoO[sub 2] whereas at pH = 5 the adsorption of Mo[sub 7]O[sup 6[minus]][sub 24] and MoO[sup 2[minus]][sub 4] ions is predominant and at pH = 4.1 the adsorption of Mo[sub 7]O[sup 6[minus]][sub 24] ions prevails. Increasing the impregnating temperature, at pH = 5, from 25 to 50[degrees]C increases considerably the adsorption of Mo[sub 7]O[sup 6[minus]][sub 24] ions and decreases further the deposition of MoO[sup 2[minus]][sub 4] ions by surface reaction, whereas it does not change considerably the extent of adsorption of MoO[sup 2[minus]][sub 4] ions. Finally, the doping with Li[sup +] and Na[sup +] ions increases both the extent of adsorption of Mo[sub 7]O[sup 6[minus]][sub 24] ions and the extent of MoO[sup 2[minus]][sub 4] deposition by surface reaction, where it does not change considerably the extent of adsorption of MoO[sup 2[minus]][sub 4] ions. Moreover, it was demonstrated that each protonated surface hydroxyl creates one adsorption site and that strong lateral interactions are exerted between the deposited species, mainly between the adsorbed MoO[sup 2[minus]][sub 4] and Mo[sub 7]O[sup 6[minus]][sub 24] ions, through water molecules located at the IHP. 34 refs., 17 figs., 3 tabs.

• OSTI ID: 7288132
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 147:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360201 -- Ceramics
Cermets
& Refractories-- Preparation & Fabrication
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
DEPOSITION
MOLYBDENUM COMPOUNDS
MOLYBDENUM OXIDES
OXIDES
OXYGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
TRANSITION ELEMENT COMPOUNDS