Vol.:(0123456789)
Reaction Kinetics, Mechanisms and Catalysis
https://doi.org/10.1007/s11144-019-01653-2
1 3
Comparative study of physico‑chemical, acid–base
and catalytic properties of vanadium based catalysts
in the oxidehydrogenation of n‑butane: effect of the oxide
carrier
Samira Slyemi, et al. [full author details at the end of the article]
Received: 31 May 2019 / Accepted: 1 August 2019
© Akadémiai Kiadó, Budapest, Hungary 2019
Abstract
Vanadium based catalysts with the following compositions: 30%V
2
O
5
–70%MgO,
30%V
2
O
5
–70%SiO
2
and 30%V
2
O
5
–40%MgO–30%SiO
2
were prepared by the wet
impregnation method using MgO and/or SiO
2
as support. The structure, texture
and morphology of the active phase strongly depend on the choice of support: for
30%V
2
O
5
–70%MgO, thin particles of Mg
3
V
2
O
8
were identified with TEM (associ-
ated to EDS) together with MgO particles while large V
2
O
5
particles beside silica
particles bearing vanadium species on their surface (EDS) were observed in the case
of the 30%V
2
O
5
–70%SiO
2
. For the 30%V
2
O
5
–40%MgO–30%SiO
2
, three crystal-
line phases were detected by XRD: Mg
3
V
2
O
8
, Mg
2
SiO
4
and MgO. Mg
3
V
2
O
8
and
Mg
2
SiO
4
were also identified with TEM-EDS with a silica-rich phase corresponding
to the silica support bearing Mg and V species on its surface. The acid–base proper-
ties of the prepared materials were evaluated by the isopropanol decomposition test.
The 30%V
2
O
5
–70%SiO
2
displays only acidic properties (formation of propene) that
can be assigned to the V
2
O
5
phase and/or to the vanadium species dispersed on sil-
ica; the 30%V
2
O
5
–70%MgO presents mainly basic properties (formation of acetone)
while the 3-components catalyst (30%V
2
O
5
–40%MgO–30%SiO
2
) displays both acid
and basic properties. The catalytic activity was investigated in the oxidehydrogena-
tion of n-butane. The selectivity to reaction products (butenes, CO
x
, cracking, isobu-
tane) is affected by the nature of surface vanadium and oxygen species, acid–base
character and the operating conditions. The best selectivities to butenes (with low
CO
x
production) were obtained on the catalysts containing magnesium, probably a
consequence of basic properties of MgO and highly dispersed magnesium-vanadium
mixed phase. The decrease of contact time favors the dehydrogenation of n-butane
to butenes especially for the V
2
O
5
–SiO
2
catalyst.
Keywords Vanadium · MgO · SiO
2
· n-Butane · Oxidehydrogenation · Acid–base
properties