Applied Catalysis A: General 245 (2003) 303–316
Characterization and reactivity of vanadium oxide
catalysts supported on niobia
Komandur V.R. Chary
a,∗
, Gurram Kishan
b
, Chinthala Praveen Kumar
a
,
Guggilla Vidya Sagar
a
, J.W. Niemantsverdriet
b
a
Catalysis Division, Indian Institute of Chemical Technology, Hyderabad 500007, India
b
Eindhoven University of Technology, Schuit Institute of Catalysis, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
Received 16 July 2002; received in revised form 8 October 2002; accepted 5 December 2002
Abstract
A series of V
2
O
5
/Nb
2
O
5
catalysts with vanadia loading varying from 2 to 12 wt.% were prepared and characterized by X-ray
diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), BET surface area and
oxygen chemisorption at 640 K. The catalytic properties have been evaluated for vapor phase ammoxidation of 3-picoline to
nicotinonitrile. XRD results suggest the formation of -(Nb,V)
2
O
5
phase at higher loadings. TPR profiles showed two peaks:
the low temperature peak is due to reduction of surface vanadia species and the high temperature peak is due to reduction
of Nb
2
O
5
. XPS results reveal that both vanadia and niobia are present in fully oxidized state (5+) in all the samples. The
intensity ratio V 2p
3/2
:Nb 3d
5/2
is found to increase with increase in vanadia loading up to 6 wt.% and to remain constant
at higher vanadia loadings. The oxygen uptake increases with increase of vanadia loading on niobia, whereas the dispersion
of vanadia decreases. The dispersion of vanadia measured by oxygen chemisorption method is in good agreement with the
dispersion determined from XPS. The ammoxidation activity increases with vanadia loading up to 6 wt.%, which corresponds
to monolayer coverage and remains constant at higher vanadia loadings. The catalytic properties during ammoxidation of
3-picoline are related to the oxygen chemisorption sites.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Vanadia–niobia catalysts; Dispersion; XPS; 3-Picoline ammoxidation
1. Introduction
Supported vanadia catalysts have been used exten-
sively for partial oxidation, ammoxidation of alkyl
aromatic compounds and selective catalytic reduction
(SCR) of NO with NH
3
[1–8]. The catalytic properties
of the active vanadia phase can be greatly influenced
by the nature of the supported oxide and the disper-
IICT communication number: 020301.
∗
Corresponding author. Fax: +91-40-27160921.
E-mail address: kvrchary@iict.ap.nic.in (K.V.R. Chary).
sion of active components. The most commonly used
supports are Al
2
O
3
, SiO
2
, TiO
2
and ZrO
2
. In recent
years, niobium-based materials have been employed
as catalysts in numerous catalytic applications [9–18].
Niobia can be used as a support, as a promoter and
as an unique solid acid. Smits et al. [16] emphasized
three reasons why niobia is an attractive support for
vanadia catalysts: (i) niobium is in the same group of
the periodic table as vanadium and is expected to have
similar properties. (ii) Niobium is much more diffi-
cult to reduce than vanadium (easy reduction often
causes low selectivity in selective oxidation reaction).
0926-860X/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0926-860X(02)00654-3