Steric aspects in methylamine and dimethylether synthesis over acidic mordenites

Shape-selective synthesis of methylamines over the RRO zeolite Al-RUB-41

“…Similar phenomena have been observed when it was attempted to selectivate a medium pore zeolite like ZSM-5 by silylation [26]. Mordenite with its larger pores is hardly or even not at all sensitive to such pore blocking upon silylation [25].…”

“…Besides methylamines, methane and dimethylether were formed as side products. Dimethylether (DME) formation has previously been ascribed to weak acid sites [25]. As part of the methanol is used for DME formation, the actual ratio of NH 3 versus available methanol is increased, and this explains the relatively high preference for MMA within the methylamine fraction.…”

“…No dimethylether was detected, which is in agreement with the availability of strong acid sites on this sample with Si/ Al = 163. In Table 2, the catalytic data for a silylated H-Mordenite sample are included for comparison [25]. Due to the silylation treatment, the pores of mordenite are narrowed, and this results in a high selectivity for MMA and DMA, with TMA selectivity as low as 6% even at a NH 3 /MeOH ratio of 1 and at high methanol conversion.…”

“…A large body of further work focused on the shape-selective properties of small pore zeolites containing typically cages that can be accessed via 8-membered ring pore windows [12][13][14][15][16][17][18][19]. Active and selective amination catalysts are for instance H-Rho, H-chabazite, and H-levyne zeolites.…”

Amination Reactions

“…In the synthesis of methylamines from methanol and ammonia, the formation of trimethylamine (TMA) is favored thermodynamically at high methanol conversion, although mainly dimethylamine (DMA) is needed commercially. However, TMA is the bulkiest product and its formation can be suppressed by steric hindrance in the channels of the properly chosen zeolite [32,[39][40][41][42], as illustrated in Table 1. The selectivity to TMA of larger pore size zeolites can be modified by ion exchange or surface passivation/pore mouth narrowing [34].…”