Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime Over Rare Earth Pyrophosphates

Abstract

A new application of rare earth pyrophosphates in vapor phase Beckmann rearrangement of cyclohexanone oxime was investigated. The rare earth phosphates were characterized by means of XRD, FT-IR, NH 3 -TPD and water contact angle measurement. It was found that the weak surface acidity and appropriate surface hydrophobicity should be two key factors in the excellent performance of these catalysts.

Reinvestigation of the Phase Equilibria in the La2O3-P2O5 System

“…They assumed that the amorphous phase starts to crystalize at 260°C to form a-La 4 (P 2 O 7 ) 3 and it changes irreversibly into the hightemperature form, b-La 4 (P 2 O 7 ) 3 , at 684°C. Gao et al [37] and Zhang et al [38] also reported that they obtained La 4 (P 2 O 7 ) 3 by similar methods. Kropiwnicka [39] [21] obtained La 4 (P 2 O 7 ) 3 by solid state reaction between La 2 (CO 3 ) 3 AE8H 2 O and NH 4 H 2 PO 4 .…”

“…In addition, since the thermal effect at 684°C on heating is exothermic and irreversible, [35] the low-temperature form of La 4 (P 2 O 7 ) 3 is considered to be in a non-equilibrium (probably metastable) state. According to several reports, [21,35,38,39] it is supposed that La 4 (P 2 O 7 ) 3 can form through the dehydration of precursors on heating.…”

Rationalising the role of solid-acid sites in the design of versatile single-site heterogeneous catalysts for targeted acid-catalysed transformations

“…19,20 Furthermore, the heterogeneous nature of the solid-acid catalysts is an added advantage from the view point of costly separations associated with the Raschig method, and circumvents the need for the neutralisation step in the work-up process. In light of this, a wide-range of materials such as TiO 2 , 21 B 2 O 3 , 22 Nb oxides, 19 tungsten oxides 23 and rare earth pyrophosphates 24 have been reported as effective catalysts for this important transformation. In particular, the use of porous zeolitic materials has been prolic, as the combination of the crystalline structure and defect silanol groups render these materials as highly active catalysts for this process.…”

Identification of Vicinal Silanols and Promotion of Their Formation on MCM-41 via Ultrasonic Assisted One-Step Room-Temperature Synthesis for Beckmann Rearrangement

“…[7][8][9] Various zeolites and mesoporous silica-alumina materials have been applied for this purpose as solid catalysts. [10][11][12][13][14][15][16][17][18][19] Zeolites containing weak Brønsted acid sites have been observed to catalyze the Beckmann rearrangement of CHO, however, their industrial application suffered from the rapid catalyst deactivation and the high reaction temperature (> 573 K) for the CPL desorption. 20,21 Surface silanol groups (SiOH) having much weaker acid strength than bridging OH groups (Si(OH)Al) in zeolites are able to catalyze the Beckmann rearrangement of CHO.…”