Synthesis of stable ECR-18 zeolite and its catalytic properties in methanol amination

Abstract

ECR-18 is the synthetic analog of paulingite (framework type PAU), a naturally-occurring cage-based, small-pore zeolite. Because of its high framework Al content (Si/Al ∼ 3), this third generation of the RHO family of embedded isoreticular zeolites is structurally unstable, thereby hampering any catalytic application. Here we present the synthesis of ECR-18 with Si/Al ratios up to 4.4 using N-methyltropinium as an organic structure-directing agent and Na+ and/or K+ as inorganic structure-directing agents. The proton form of ECR-18 with Si/Al = 4.4 was found to retain the structural integrity. The catalytic properties of this ECR-18 for methylamines synthesis from ammonia and methanol have been compared with those of H-rho and H-PST-29, the two most selective catalysts for this reaction. Despite the similarity in acidity, H-ECR-18 showed a low sum yield of monomethylamine and dimethylamine compared to H-PST-29, mainly due to the lower ratio of scaffold (i.e., lta, pau, d8r, and t-plg) cages to embedded (i.e., t-oto, t-gsm, and t-phi) cages per unit cell of the former zeolite catalyst.