Molybdenum-oxo species deposited on titania by adsorption: Mechanism of the adsorption and characterization of the calcined samples

Journal Article · Sat Aug 01 04:00:00 EDT 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90074-R· OSTI ID:7241514

Spanos, N; Matralis, H K; Kordulis, Ch; Lycourghiotis, A ^[1]

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1. Inst. of Chemical Engineering, Patras (Greece)

The mechanism of the adsorption of molybdates on the titania surface has been investigated using adsorption equilibrium experiments, potentiometric titrations, and microelectrophoretic mobility measurements. Comparison of adsorption data with the surface change of titania, regulated by changing the pH of the impregnating solution, demonstrated that the groups responsible for the creation of the adsorption sites are mainly the protonated surface hydroxyls of titania in addition to the neutral sites. Moreover, results suggested that the MoO{sub 4}{sup 1{minus}} ions are adsorbed on the Inner Helmholtz Plane (IHP) of the electrical double layer, which is developed between the surface of the titania particles and the impregnating solution. Finally, from the analysis of the isotherms obtained it was concluded that the adsorbed MoO{sub 4}{sup 2{minus}} ions are located on energetically equivalent sites of the IHP and that relatively weak lateral interactions are exerted. An explanation of the dependence of the sorptive capacity of titania on the pH on the impregnating solution is provided. The combined use of NO and CO{sub 2} adsorption, as well as XPS, RAMAN spectroscopy, and temperature programmed reduction measurements, showed that at pH 7.3, corresponding to about 2 wt% MoO{sub 3}, the titania surface is completely covered and the active surface reaches its maximum value. At pH values lower than 7.3, a second molybdena layer starts to form until the MoO{sub 3} content reaches the 5.4 wt% MoO{sub 3}, a point at which MoO{sub 3} crystallites are formed.

• OSTI ID: 7241514
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 136:2; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ADSORPTION
CALCINATION
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CATALYSTS
CHALCOGENIDES
CHEMICAL REACTIONS
CONTROL
CRYSTALLIZATION
DECOMPOSITION
ELECTRON SPECTROSCOPY
ELECTROPHORESIS
IMPREGNATION
KINETICS
LASER SPECTROSCOPY
LAYERS
MOLYBDATES
MOLYBDENUM COMPOUNDS
MOLYBDENUM OXIDES
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
PH VALUE
PHASE TRANSFORMATIONS
PHOTOELECTRON SPECTROSCOPY
POTENTIALS
POTENTIOMETRY
PYROLYSIS
RAMAN SPECTROSCOPY
REDUCTION
REFRACTORY METAL COMPOUNDS
SORPTION
SORPTIVE PROPERTIES
SPECTROSCOPY
SURFACE POTENTIAL
SURFACE PROPERTIES
TEMPERATURE CONTROL
THERMOCHEMICAL PROCESSES
TITANIUM COMPOUNDS
TITANIUM OXIDES
TITRATION
TRANSITION ELEMENT COMPOUNDS
X-RAY SPECTROSCOPY