Selective synthesis of dimethylamine over small-pore zeolites: II. Effects of impurities on catalytic properties of H-RHO

• Published in: Journal of catalysis 1988, Vol.114 (1), p.8-16
• Main Authors: Shannon, R.D., Keane, M., Abrams, L., Staley, R.H., Gier, T.E., Corbin, D.R., Sonnichsen, G.C.
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts: preparations and properties; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; General. Nomenclature, chemical documentation, computer chemistry; Theory of reactions, general kinetics; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(88)90003-6

Typical RHO preparations can contain impurities such as unreacted gel, chabazite, P c, and pollucite. These impurities were synthesized in pure form to investigate their effects on the behavior of RHO as a dimethylamine (DMA)-selective catalyst in the methanol-ammonia reaction. Gel and p c, after exchange and calcination, were amorphous and inactive at typical reaction temperatures of 300–325 °C. Chabazite, always present in RHO preparations at 5–10% levels, is active and DMA selective after deep-bed calcination. After shallow-bed calcination, it loses much of its crystallinity and becomes inactive. Pollucite, appearing in the later stages of RHO crystallization, loses activity at 325 °C after shallow-bed calcination. However, after deep-bed calcination, it is an active and nonselective methylamine catalyst. Thus, the presence of pollucite can be a primary cause of lower DMA selectivity of deep-bed calcined RHO catalysts. Steaming, one of the most effective methods of reducing the activities of impurities, destroys pollucite crystallinity and/or nonselective Surface sites.