M. Agunaou et al., Effect of the Gd substitution by Bi in the BixGd1-xVO4 catalysts on the catalytic behaviour of methanol oxidation, APP CATAL A, 196(1), 2000, pp. 87-92
A series of Bi-x Gd1-x VO4 mixed oxide has been prepared by coprecipitation
and characterised by XPS, IR spectroscopy and by the reaction of methanol
oxidation used as a catalytic surface probe. Within the tetragonal phase do
main (0 less than or equal to x less than or equal to 0.64), zircon-type an
d scheelite-type structures are observed for x less than 0.3 or higher than
0.3, respectively. The zircon-type phase shows higher selectivities in met
hyl formate and carbon dioxide than the scheelite-type phase which mainly f
orms formaldehyde. The selectivities in methyl formate and carbon dioxide i
ncrease with the bismuth content in the zircon-type phase domain. Whatever
these structures, the gadolinium substitution by the larger size bismuth ca
tion induces an effect similar to that of the external pressure, leading to
a shortening of the Bi-O and Gd-O distances which tends to increase the el
ectronic density on these cations. However, a Bi --> VO4 charge transfer wh
ich occurs in the Bi-O-V group partly compensates the preceding effect. (C)
2000 Elsevier Science B.V. All rights reserved.