Temperature-programmed reduction and oxidation of nickel supported on WO3–Al2O3composite oxides
Southmayd, D. W.; Contescu, Cr.; Schwarz, J. A.
Журнал:
Journal of the Chemical Society, Faraday Transactions
Дата:
1993
Аннотация:
A series of Ni/WO3â Al2O3 catalysts have been prepared by systematically varying the weight loading of WO3â Al2O3 and the pH during adsorption/impregnation. The catalysts developed an increased interaction between the impregnated nickel and the supported metal oxide; the charge on the mixed oxide resulted in the impregnated nickel cation to be preferentially adsorbed onto tungsten sites of the composite supports. The amount of nickel associated with tungsten oxide was found to be a function of both the tungsten oxide weight loading and the impregnation pH. An increase in the negative charge due to hydrolysis of the tungsten oxide phase in the aqueous impregnant is proposed to result in a tungsten oxide associated nickel that is twice as large for the catalysts prepared at pH 6 than that at pH 4. The Ni/support interaction formed during adsorption/impregnation and drying were studied by temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO). The tungsten oxide and associated nickel were found to form a nickel tungstate compound which reacted with H2 at ca. 1050 K but could be regenerated by TPO. An Ni/Al2O4 type surface compound was also formed that was reduced at ca. 1150 K.
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