2 5
with La leads to a less crystalline and defect-rich V O lattice
which seems to be the best suited for this reaction. These
results are in accordance to the XPS investigations showing a
V-enriched surface offering the best catalytic performance.
In addition, the long-term behaviour of this catalyst was
also tested for a period of 10 h on-stream. The conversion of
MP is almost constant at 100% throughout. However, the
yield of CP is slightly increased on-stream and then remained
constant at around 86%, which indicates that the catalyst
attained steady state conditions. Furthermore, it can be noticed
that there is no deactivation over a period of 10 h.
In conclusion, it can be stated that different metal cations in
the vanadates lead to different enrichment of V in the near
surface region. Such variation of the surface composition
clearly offered the possibility of enhancing the catalytic
performance of the vanadates in terms of conversion and
selectivity in the ammoxidation of MP. After proper optimiza-
tion, very high yields of CP (86%) with remarkably high
Fig. 2 Correlation between surface V/Me ratios and catalytic perfor-
mance (X-MP: conversion of 2-methylpyrazine; S-CP: selectivity of
2-cyanopyrazine) and temperature at total conversion.
À1
À1
À1
space-time-yields (ca. 525 gCP kgcat
h ) at almost total
conversion of MP could be successfully obtained, which is
to our knowledge the best STY value reported so far for this
reaction. The systematic optimization of the solids shows that
2 5
La doped V O is the best suitable system.
We thank M. Schneider and W. Winkler for the XRD results.
Notes and references
1
2
G. Ertl, Reactions at Solid Surfaces, Wiley & Sons, 2009.
D. D. Suresh, M. S. Friedrich and M. J. Seely, (Standard Oil Co.
Ohio), US 5212137, 1993; F. Cavani, G. Centi and P. Marion,
in Metal Oxide Catalysis, ed. S. D. Jackson and S. J. Hargreaves,
Wiley-VCH, Weinheim, 2009, vol 2, p. 771; A. Martin and
V. N. Kalevaru, ChemCatChem, 2010, 2, 1504; V. N. Kalevaru,
¨
B. Lucke and A. Martin, Catal. Today, 2009, 142, 158.
3
4
5
A. D. Kagarlitskii, L. A. Krichevskii and A. K. Amirkhanova,
Pharm. Chem. J., 1999, 33, 381.
Fig. 3 Catalytic results of the ammoxidation of 2-methylpyrazine
using various LaVO catalysts with varying La/V ratios; X-MP =
conversion of 2-methylpyrazine; Y-CP = yield of 2-cyanopyrazine;
Y-COx = yields of CO and CO ; STY = space-time-yield.
L. Forni, Appl. Catal., 1986, 20, 219; L. Forni, C. Oliva and
C. Rebuscini, J. Chem. Soc., Faraday Trans. 1, 1988, 84, 2397.
V. B. Bondareva, T. V. Andrushkevich, E. A. Paukshtis,
N. A. Paukshtis, A. A. Budneva and V. N. Parmon, J. Mol. Catal.
A: Chem., 2007, 269, 240; V. M. Bondareva, T. V. Andrushkevich,
O. B. Lapina, D. F. Khabibulin, A. A. Vlasov, L. S. Dovlitova and
E. B. Burgina, Kinet. Catal., 2004, 45, 104.
x
2
0.7 x
and reached almost 100% on La0.3V O catalysts. Afterwards,
the conversion remained unaltered, while the yield of CP has been
substantially increased further with increase in the vanadium
content of the catalyst up to 0.1 : 0.9 La : V mole ratio.
6 V. M. Bondareva, T. V. Andrushkevich, L. G. Detusheva and
G. S. Litvak, Catal. Lett., 1996, 42, 113; K. N. Rao, K. M. Reddy,
N. Lingaiah, I. Suryanarayana and P. S. Sai Prasad, Appl. Catal.,
A, 2006, 300, 139; N. Lingaiah, K. Mohan Reddy, P. Nagaraju,
P. S. Sai Prasad and I. E. Wachs, J. Phys. Chem. C, 2008,
112, 8294; K. Mohan reddy, N. Lingaiah, P. S. N. Rao,
P. Nagaraju, P. S. Sai Prasad and I. Suryanarayana, Catal. Lett.,
However, further increase in the vanadium content causes a
a b x
decrease in the yield of CP. Among different La V O solids,
the catalyst with 0.1 : 0.9 La : V mole ratio (i.e. La0.1V0.9Ox)
exhibited the superior performance. The best yield of CP
is found to be 86% at almost total conversion of MP.
Additionally, the best space-time-yield (STY) of CP of ca.
2
009, 130, 154.
7
P. Nagaraju, N. Lingaiah, M. Balaraju and P. S. Sai Prasad, Appl.
Catal., A, 2008, 339, 99; P. Nagaraju, Ch. Srilakshmi, N. Pasha,
N. Lingaiah, I. Suryanarayana and P. S. Sai Prasad, Appl. Catal.,
A, 2008, 334, 10.
B. P. Barbero and L. E. Cadus, Appl. Catal., A, 2003, 244, 235;
S. Sugiyama, T. Hashimoto, Y. Morishita, N. Shigemoto and
H. Hiyashi, Appl. Catal., A, 2004, 270, 253.
À1
À1 À1
5
25 gCP kgcat
h
was obtained for the first time. This is the
highest value obtained so far compared to all other existing
À1 À1
h ,
8
9
1
3
7
À1
literature on this reaction (e.g. 300 and 140 gCP kgcat
respectively). Pyrazine, pyrazinamide, CO and CO
2
were
L. E. Briand, J.-M. Jehng, L. Cornaglia, A. M. Hirt and
I. E. Wachs, Catal. Today, 2003, 78, 257.
0 N. Dhachapally, V. N. Kalevaru and A. Martin, EP 10175734, 2011.
observed as by-products. Pyrazine formation is from the
demethylation of MP occurring usually on stronger acidic
sites. Pyrazinamide formation is expected from hydrolysis of
1
11 O. S. Owen and H. H. Kung, J. Mol. Catal., 1993, 79, 265;
M. C. Kung and H. H. Kung, J. Catal., 1992, 134, 668.
CP. CO and CO are a result of unavoidable total oxidation.
2
1
2 S. V. Merzlikin, N. N. Tolkachev, L. E. Briand, T. Strunskus,
C. Woll, I. E. Wachs and W. Grunert, Angew. Chem., Int. Ed.,
2010, 49, 8037.
13 US 4,496,729 (1985) Degussa AG.
The XRD of this catalyst (i.e. La0.1V0.9O ) shows only the
x
¨
¨
reflections typical for V O (Fig. S2, ESIw), but less intense
2
5
and sharp compared with pure V O . The doping of V O
5
2
5
2
8
396 Chem. Commun., 2011, 47, 8394–8396
This journal is c The Royal Society of Chemistry 2011