173 research outputs found
Vapor phase Beckmann rearrangement using high silica zeolite catalyst
Vapor phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam has been studied using high
silica zeolite catalysts. Catalysts with different crystal sizes and gel-ageing times have been activated by ionic
exchange in different conditions by means of a highly basic solution and a nearly neutral solution both
containing ammonium salts. Samples have been calcined at different temperatures in order modify the number
of defective sites. We observed that samples exchanged by means of a highly basic solution (pH > 10)1,2 and
calcined at a relatively lower temperature (450 C) show the most interesting catalytic results. X-ray powder
diffraction patterns of these samples show2 retention of the unit cell symmetry (orthorhombic cell) if compared
to the dried sample. NH3-TPD confirms the low acidity of high silica zeolites, however a higher amount of
desorbed ammonia is observed for the samples exchanged at higher pH and calcined at 450 C. Due to silanol
nests the IR spectra of the same samples show the formation of Si\u2013NH2 bonds which are absent in the
same material exchanged by other methods. Such sites seem to promote the high stability of the high silica
zeolite catalysts also to the regeneration which is needed to remove the heavy carbonaceous compounds
from the catalyst surface
The control of catalytic performance of rutile-type Sn/V/Nb/Sb mixed oxides, catalysts for propane ammoxidation to acrylonitrile
This paper describes the effect of the composition of rutile-type Sn/V/Nb/Sb mixed oxides catalysts on the
catalytic performance in the gas-phase ammoxidation of propane to acrylonitrile. The variation in the
atomic ratio between components in catalysts is the key for the control of activity and selectivity. In
samples with atomic composition Sn/V/Nb/Sb 1/0.2/1/x (0 x 5) and 1/0.2/y/3 (0 y 3) several
compounds formed, i.e., SnO2, Sb/Nbmixed oxide, Sb6O13 and non-stoichiometric rutile-type V/Nb/Sb/O;
the latter segregated preferentially at the surface of the catalyst. Tin oxide provided the rutile matrix for
the dispersion of the mixed oxides. The main role of Sb was shown to generate mixed oxides containing
specific sites for the allylic ammoxidation of propylene intermediately formed. The presence of Nb
enhanced the activity and selectivity of these sites
Aree industriale ad alto rischio chimico: loro eventuale riconversione e aspetti di sicurezza industriale
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