Microwave and ultrasonic synthesis of vanadium-containing oxidative
catalyst precursors
V.Sydorchuk1, S.Khalameida1, J.Skubiszewska-Zięba2 , R.Leboda2, V.Zazhigalov1
1
Institute for Soption and Problems of Endoecology NAS of Ukraine, 13 Naumova Str., 03164
Kyiv, Ukraine
2
Faculty of Chemistry, Maria Curie-Skłodowska University, pl. Marii Curie-Skłodowskiej 3,
2-031 Lublin, Poland
e-mail: bilychi@ukr.net
The hydrothermal treatment (HTT) assisted microwave heating named microwave
technique (MWT) and ultrasonic treatment (UST) belong to non-conventional methods of
green chemistry which are used for synthesis of organic and inorganic substances. MWT has
some significant advantages in comparison with usual HTT: i) acceleration of reaction rate
(i.e. lowering time and energy usage), ii) mild reaction conditions, iii) uniform distribution of
heat on whole reaction volume. In UST method the solid phase subjects additional intensive
dynamical influence of local and impact temperature elevation. Both presented approaches
were applied sufficiently for the catalysts preparation.
The study of influence of MWT (and HTT – for comparison) and UST on synthesis
and properties of some vanadium-containing catalyst precursors presented in this
communication. Bulk and deposited samples of V-Mo-O, V-Mo-Nb-O and V-P-O systems
were synthesized by MWT method in aqueous medium at temperature 150-250˚C and
pressure 3-10 MPa for 0,5-1 h from oxides and ammonium salts. UST method was realized in
aqueous medium at 20KHz and 80˚C for 1-2 h. Prepared precursors and products of their
calcinations were investigated by means of XRD, DTA-TG, FTIR, nitrogen adsorption
measuring, mercury porosimetry, SEM methods.
The obtained results show a significant acceleration (in the 5-10 times) of precursor
structure formation at MWT in comparison to traditional solid state interaction and even HTT.
It was established that owing to decrease of time for re-crystallization (Ostwald ripening)
MWT synthesized samples posses higher value (on 30-40 %) of specific surface area. Well
developed hierarchically built porosity presented by meso- and macro-pores, which is very
important for catalysts, formed in samples prepared via MWT. Thus pore volume for V-Mo-O
and V-Mo-Nb-O compositions after MWT achieves 1,0-1,5 ml/g while after HTT synthesis
this parameter as a rule does not exceed 0,5 ml/g. The following calcinations of prepared by
MWT (HTT) precursors under 300-500˚C accompanied by formation of active phase of the
catalysts. For example, the phase V2MoO8, which is base of some oxidation catalysts, was
generated under lower temperature in comparison to solid state reaction in V-Mo-O system.
Besides it was established that calcined samples retain developed porosity – pore volume
equals 0,8-1,0 ml/g. So the use of MWT method permits to regulate in wide ranges the
parameters of porous and crystal structure (crystallite size, primary surface orientation of
crystal planes) of the catalysts. Microwave deposition of VPO-phase on silica and carbon
supports results to formation on their surface of vanadylhydrophosphate hemyhydrate phase
(precursor of catalyst) composed from crystallites with various size, morphology and surface
content of planes. These catalysts can be used in oxidation or oxidative dehydrogenation
processes depending on value of the latter parameter.
The peculiarity of UST method at synthesis of mixed V-Mo oxides is formation of
mesoporous samples with pore volume 0,30-0,40 ml/g from initial coarsely dispersed
nonporous powders.
Acknowledgment. This work was partly supported by International Visegrad Fund
(Contract No 50810086).