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New non-zeolitic Nb-based catalysts for the gas-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam

“…The catalytic activity relationship to the acidity of the catalyst materials was intensively studied previously. Some of the authors claimed that strong acid sites were responsible for high catalytic activity [46]. In contrast, Hoelderich et al [3,[15][16][17][18]33] reported that weakly acidic vicinol silanol groups and nest silanol sites are favorable for high activity and excellent catalytic performance in the gas-phase Beckmann rearrangement.…”

Deactivation and regeneration of the BO/TiO-ZrO catalyst in the vapor phase Beckmann rearrangement of cyclohexanone oxime

“…Then the catalytic behavior is mainly determined by acidity: the conversion of cyclohexanone oxime is closely correlated with the number of acid sites of medium strength, which are characterized by desorption of adsorbed ammonia between 200 and 350 • C [44]. It should be emphasized here that the acidity requirement for the vapor-phase rearrangement reaction on zeolites and supported catalysts, such as B 2 O 3 [3,8], Ta 2 O 5 [9] and WO 3 [10] is quite different. For these supported catalysts, it has been well demonstrated that the acid sites of intermediate strength are responsible for selective formation of caprolactam [3,8,9,37].…”

“…A preferable alternative is to perform the Beckmann rearrangement reaction in the vapor phase using solid acid instead of sulfuric acid as a catalyst. In the past two decades, a large number of solid acid catalysts have been studied such as boria supported on various carriers [1][2][3][4][5][6][7][8], silicasupported tantalum oxide and tungsten oxide [9,10], alumina pillared montmorillonite [11], tantalum pillared ilerite and magadiite [12][13][14], boron hydrotalcite-like compounds [15], SiMCM-41-supported phosphotungstic acid [16], anionic clays [17] and a wide variety of zeolites, such as USY [18], ZSM-5 [19][20][21][22][23][24][25], ZSM-11 [26], SAPO-11 [27], Beta [28,29], LTL [30], ferrierite [31] and MCM-22 [32], and mesoporous molecular sieves such as MCM-41, MCM-48, FSM-16 and SBA-15 [33][34][35][36][37][38][39].…”

“…It is very important to note that the calcination temperature for the preparation of the supported B 2 O 3 catalysts in which loss or structural modification of B 2 O 3 occurred in the regeneration process was relatively low, i.e. 350 • C[2,3,10,62,63] or 500 • C[4]. Nevertheless, those boria catalysts in which no loss or structural modification of B 2 O 3 occurred during the regeneration process were all prepared by calcining at a high temperature, i.e.…”

Nanosized and delayered zeolitic materials for the liquid-phase Beckmann rearrangement of cyclododecanone oxime

“…Rapid catalyst deactivation is observed, however, with conversion on dropping to <50% after 4 h TOS. According to studies carried out for the Beckmann rearrangement with other oximes [35][36][37][38][39], significant lactam adsorption can occur, leading to polymerization and eventually to coke. We studied the chloroform-extracted catalyst by 13 C CP-MAS-NMR spectroscopy and found that the organic deposit is formed mainly of LRL and/or its higher isomers.…”