Three tetra-n-butylammonium
(TBA) salts of polyvanadotungstates,
[n-Bu4N]6[PW9V3O40] (PW
9
V
3
), [n-Bu4N]5H2PW8V4O40 (PW
8
V
4
), and [n-Bu4N]4H5PW6V6O40·20H2O (PW
6
V
6
), have been synthesized and shown to be effective
catalysts for the aerobic oxidation of formaldehyde to formic acid
under ambient conditions. These complexes, characterized by elemental
analysis, Fourier transform infrared spectroscopy, UV–vis spectroscopy,
and thermogravimetric analysis, exhibit a catalytic activity for this
reaction comparable to those of other polyoxometalates. Importantly,
they are more effective in the presence of water than the metal oxide-supported
Pt and/or Au nanoparticles traditionally used as catalysts for formaldehyde
oxidation in the gas phase. The polyvanadotungstate-catalyzed oxidation
reactions are first-order in formaldehyde, parabolic-order (slow,
fast, and slow again) in catalyst, and zero-order in O2. Under optimized conditions, a turnover number of ∼57 has
been obtained. These catalysts can be recycled and reused without
a significant loss of catalytic activity.