Shape-selective methylamine synthesis over small-pore zeolite catalysts

Methylamine syntheses from methanol and ammonia on various zeolite catalysts have been studied over a temperature range of 573-673 K. The H-chabazite catalyst gives enhanced yield of monomethylamine at higher partial pressures of ammonia, while the formation of trimethylamine and dimethyl ether has been extremely retarded, Sorption-desorption experiments reveal nearly complete exclusion of TMA from the chabazite cages. Sorption and IR spectroscopic data provide evidence that the initial methylamine formation involves methanol and ammonia that are both bound to Bronsted acid sites and follows a Langmuir-Hinshelwood mechanism, in contrast to the Eley-Rideal mechanism that is observed with large pore zeolites or other solid catalysts. Transition state selectivity, rather than product selectivity, is invoked as the main cause for the preponderance of monomethylamine and dimethylamine and the almost complete suppression of trimethylamine. (C) 1996 Academic Press, Inc.