conditions, i.e., with 10% n-butane and 17% oxygen in feed. As shown in Figure 1 (left), there
Doping vanadyl pyrophosphate with NbV: improved efficiency of
was only a minor effect on n-butane conversion, but the yield to maleic anhydride was higher with the Nb-doped system, especially at temperatures higher than 400°C. The higher selectivity
the catalyst for n-butane oxidation to maleic anhydride
did correspond to the decrease of selectivity to both COx and phthalic anhydride. It is worth
noting that the formation of phthalic anhydride, a minor compound under hydrocarbon-lean
Aurora Caldarelli1, Francesca Pierelli1, FabrizioCavani1*, Carlotta Cortelli2, and Federico
conditions, but an important one at hydrocarbon-rich conditions, derives from the Diels-Alder
type reaction between maleic anhydride and butadiene, the latter being an intermediate
1Diaprtimento di Chimica Industriale e dei Materiali, Viale Risorgimento 4, ALMA MATER STUDIORUM Università di Bologna, 40136 Bologna, Italy
In order to explain the better efficiency of the Nb-doped catalyst in maleic anhydride formation,
2Polynt SpA, Via E. Fermi 51, 20097 Scanzorosciate (BG), Italy
we carried out in-situ Raman experiments on the V/P/O catalysts. We found that the Nb-doped
VPP developed the desired δ-VOPO4 during heating in air at 380°C (Figure 1, right); on the opposite, the undoped VPP developed the desired oxidized phase only after treatment in an
Introduction
air/steam flow, an environment that favoured the transformation of the VPP to δ-VOPO4 via
Vanadyl pyrophosphate is the main component of the industrial catalyst for the selective
hydrolysis to VOPO4.2H2O. We concluded that the enhanced formation of the desired δ-
oxidation of n-butane to maleic anhydride. Various structural and morphological characteristics
VOPO4 was the reason for the better selectivity shown by the Nb-doped catalyst; in fact, the
affect the catalytic behavior of the V/P/O system, but the most important one is the presence of
transformation of the intermediately formed butadiene into maleic anhydride turned out to be
a slight excess P with respect to the stoichiometric amount required for the vanadyl
more favoured, because of the higher concentration of the selective δ-VOPO4 compound.
pyrophosphate formation. In this regard, we recently reported that the key point to obtain a
moderately active but highly selective catalyst is the in-situ generation, under reaction
conditions, of discrete amounts of δ-VOPO
4 on the vanadyl pyrophosphate surface, and that the
generation of this VV phosphate is favoured in the presence of the forementioned P excess [1,2].
In order to further improve the catalytic performance of the industrial catalyst, we doped the
Sel MA, Nb-doped VPP
vanadyl pyrophosphate with controlled amounts of a NbV compound, precursor for the
o, Mnnio 40 1083
generation of Nb or mixed Nb/VV phosphate [3]. The latter compound might facilitate the
1013 1039 Nb-doped VPP C4 conv, VPP Experimental
The V/P/O catalyst was prepared according to the procedure described in refs [1,2]; the Nb-
Sel MA, VPP
doped V/P/O were prepared by addying the desired amount of NbCl
2O5, H3PO4 and isobutanol, raw materials for the the synthesis of the vanadyl pyrophosphate
precursor. Catalysts were prepared with atomic V/Nb ratio equal to 44. Catalysts were
characterized by means of X-ray Diffraction, Raman Spectroscopy and UV-Vis Diffuse
Figure 1. Left: n-butane conversion and selectivity
Reflectance. Catalytic experiments were carried out in a continuous flow reactor; different inlet
to MA of Nb-doped VPP and undoped VPP under
feed compositions were used, either n-butane lean (1% n-butane, 17% oxygen, remainder He),
hydrocarbon reach conditions. Right: in-situ Raman 1
or n-butane-rich (10% n-butane, 17% oxygen, remainder He).
spectra of Nb-doped VPP recorded in function of T
Results/Discussion References
Doping the V/P/O catalyst with Nb had important implications on the catalytic behavior. Under
F. Cavani, S. Luciani, E. Degli Esposti, C. Cortelli, and R. Leanza, Chem. Eur. J., 16,
hydrocarbon-lean conditions, e.g., with 1.7% n-butane in feed, the improvement was that of an
increase of n-butane conversion, with respect to the undoped system. Since the selectivity to
F. Cavani, D. De Santi, S. Luciani, A. Lofberg, E. Bordes-Richard, C. Cortelli, and R.
maleic anhydride did not decrease, the activity increase led to an higher yield to the desired
Leanza, Appl. Catal. A, 376, 66 (2010).
compound. Even more remarkable was the effect of Nb doping under hydrocarbon-rich
F. Cavani, F. Pierelli, F. Ghelfi, G. Mazzoni, and C. Fumagalli, EP 1514598 (2003).
Innovation, Education, Quality Assessment, Continual Improvement P l e ur al fl ui d : Stre pt oc oc cu s pne u mo n i a e –multi re sistan t strain “susceptible” by 12/15 reference labs. Given that vancomycin reporting may depend on the This sample simulated a pleural fluid from a 1 penicillin and/or cephalosporin results, where Virtually all labs isolated and year old patient wi