382
W. Piskorz and F. Zasada
where all the support is covered by dispersed oxide species and also some V 2 O 5
nanoparticles can be present [415, 416].
Such insights into the V 2 O 5 status in supported catalytic systems allow for identifying the active phases, thus enable the molecular engineering and tuning by controlling the number of catalytic active sites on the support and their specific activity
[417–419].
Catalytic Activity
The catalytic properties of vanadia and vanadia-based materials are mainly selective
oxidation reactions with the generally accepted “nucleophilic” mechanism in which
lattice oxygen participates in the reaction by being incorporated into the organic
species [420]. The resulting oxygen vacancies may be refilled by dioxygen following
the MvK mechanism, or the defect concentration exceeds a critical value, resulting
in the vanadia surface topology change [421, 422]. Thus, supported vanadium oxide
catalysts have found extensive applications as oxidation catalysts in the chemical,
petroleum, and environmental industries [415]. An SiO 2 -supported vanadia catalyse
the oxidation of sulphur dioxide to sulphur trioxide in the production of sulphuric
acid [423, 424]. Supported V 2 O 5 /TiO 2 system, consisting of a 2D surface vanadium oxide phase strongly interacting with the TiO 2 support, represents a new class
of catalytic materials [425, 426] with large number of applications. It is used for
selective oxidation of o-xylene to phthalic anhydride, selective oxidation of alkyl
pyridines to nicotinic acid and selective catalytic reduction (SCR) of NO x emissions
with ammonia or urea [426]. Commercial V 2 O 5 -WO 3 /TiO 2 shows good catalytic
activity because of its highly stable activity for NO x removal and low sensitivity to
SO 2 poisoning [427, 428]. It has also been found to activate oxidative destruction
of chlorinated hydrocarbons [429] and oxidation of elemental mercury to mercury
oxides that are easier to trap. The V 2 O 5 /Al 2 O 3 catalysts were applied for oxidative
dehydrogenation of propane to propene [430]. Vanadium-based catalysts supported
on sulphated or tungstated ZrO 2 were used for SCR of NO showing improved potassium poisoning resistance compared to traditional titania-supported system [431].
Thorough understanding of the catalyst active phase on the molecular level may be
achieved only by cooperation of surface science experiments and molecular modelling techniques.
Computational Issues
In the work of Kempf et al. [432], the periodic structure of V 2 O 5 has been optimised
with employment of Hartree–Fock method, with good agreement for the structural
parameters and for the vanadyl bond stretching force constant, but with much too low
binding energy calculated. The latter parameter may be improved by the employment
of the GGA-based DFT [433]. In the LDA calculation [434], the resulting bulk
structure was well reproduced—the atomic coordinates agree up to 0.01 Å, and the
W. Piskorz and F. Zasada
where all the support is covered by dispersed oxide species and also some V 2 O 5
nanoparticles can be present [415, 416].
Such insights into the V 2 O 5 status in supported catalytic systems allow for identifying the active phases, thus enable the molecular engineering and tuning by controlling the number of catalytic active sites on the support and their specific activity
[417–419].
Catalytic Activity
The catalytic properties of vanadia and vanadia-based materials are mainly selective
oxidation reactions with the generally accepted “nucleophilic” mechanism in which
lattice oxygen participates in the reaction by being incorporated into the organic
species [420]. The resulting oxygen vacancies may be refilled by dioxygen following
the MvK mechanism, or the defect concentration exceeds a critical value, resulting
in the vanadia surface topology change [421, 422]. Thus, supported vanadium oxide
catalysts have found extensive applications as oxidation catalysts in the chemical,
petroleum, and environmental industries [415]. An SiO 2 -supported vanadia catalyse
the oxidation of sulphur dioxide to sulphur trioxide in the production of sulphuric
acid [423, 424]. Supported V 2 O 5 /TiO 2 system, consisting of a 2D surface vanadium oxide phase strongly interacting with the TiO 2 support, represents a new class
of catalytic materials [425, 426] with large number of applications. It is used for
selective oxidation of o-xylene to phthalic anhydride, selective oxidation of alkyl
pyridines to nicotinic acid and selective catalytic reduction (SCR) of NO x emissions
with ammonia or urea [426]. Commercial V 2 O 5 -WO 3 /TiO 2 shows good catalytic
activity because of its highly stable activity for NO x removal and low sensitivity to
SO 2 poisoning [427, 428]. It has also been found to activate oxidative destruction
of chlorinated hydrocarbons [429] and oxidation of elemental mercury to mercury
oxides that are easier to trap. The V 2 O 5 /Al 2 O 3 catalysts were applied for oxidative
dehydrogenation of propane to propene [430]. Vanadium-based catalysts supported
on sulphated or tungstated ZrO 2 were used for SCR of NO showing improved potassium poisoning resistance compared to traditional titania-supported system [431].
Thorough understanding of the catalyst active phase on the molecular level may be
achieved only by cooperation of surface science experiments and molecular modelling techniques.
Computational Issues
In the work of Kempf et al. [432], the periodic structure of V 2 O 5 has been optimised
with employment of Hartree–Fock method, with good agreement for the structural
parameters and for the vanadyl bond stretching force constant, but with much too low
binding energy calculated. The latter parameter may be improved by the employment
of the GGA-based DFT [433]. In the LDA calculation [434], the resulting bulk
structure was well reproduced—the atomic coordinates agree up to 0.01 Å, and the