Vapor phase Beckmann rearrangement using high silica zeolite catalyst

Abstract

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 show 2 retention of the unit cell symmetry (orthorhombic cell) if compared to the dried sample. NH 3-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-NH 2 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.

Enhanced propene/ethene selectivity for methanol conversion over pure silica zeolite: Role of hydrogen-bonded silanol groups

“…S5). Two broad resonance signals are observed with chemical shifts at −113 and −103 ppm, which belong to SiO 4 groups and nest of silanols or bridged silanols, respectively [22].…”

Substrate inhibition in the heterogeneous catalyzed aldol condensation: A mechanistic study of supported organocatalysts

“…Indeed, the weakly acidic silanol groups on the surface of silica have been previously recognized as capable of assisting various reactions. [23,[45][46][47][48][49] To test the participation of silanol groups in the catalytic process, we treated MAP-MSN-3.5 with hexamethyldisilazane (HMDS). 29 Si NMR showed that this reduced the number of silanols by 39% (from 3.8 to 2.3 mmol/g, Figure 4).…”

Influence of Na+ on the synthesis of silicalite-1 catalysts for use in the vapor phase Beckmann rearrangement of cyclohexanone oxime

“…No peaks corresponding to Na-containing phases were detected. All samples show reflections at 2θ = 24.4°, indicating that the typical structures of S-1-Na-x have monoclinic symmetry [8,14]. The relative crystallinity of the base treated S-1-Na-x samples were calculated by comparing the total intensity values for the peaks at 2θ = 7.9°, 8.9°, 23.0°, 23.2°, 23.7°a nd 24.0° [39] and assuming that those of S-1-Na-0 represent 100%.…”

“…Molecular sieves have also been widely investigated for this reaction [3,. Among these, MFI-type zeolites [8][9][10][11][12][13][14][15][18][19][20][21][23][24][25]28,32] with high Si/Al ratios and silicalite-1 (S-1) have been found to be active and selective for this reaction. Sumitomo Chemical Co., Ltd. has commercialized the vapor phase Beckmann rearrangement of cyclohexanone oxime using S-1 as the catalyst [23].…”