Novel silicoaluminophosphate molecular sieves with CHA/GME intergrowth structures: synthesis, structural elucidation and catalytic application

Abstract

Two novel SAPO molecular sieves, designated as DNL-8 and DNL-9, were synthesized via an aminothermal co-templating strategy. This approach employed diisopropanolamine (DIPA) as both the solvent and the primary organic structure-directing agent (OSDA), with benzyltrimethylammonium chloride (BTACl) or trimethylamine (TMA) serving as a co-OSDA. ¹³C MAS NMR results demonstrate that the organics occluded in the crystals are a combination of TMA and DIPA for both samples. Three-dimensional (3D) rotation electron diffraction (RED) was used to elucidate their structures, revealing that both DNL-8 and DNL-9 are the intergrowths of the CHA/GME framework. In combination with the simulated XRD patterns of the intergrowths, the GME/CHA ratio is estimated to be 80% GME/20% CHA for DNL-8 and 20% GME/80% CHA for DNL-9. Interestingly, DNL-9 exhibits good catalytic performance in the methanol amination reaction with an ultrahigh selectivity toward monomethylamine (MMA) and dimethylamine (DMA) (∼96 wt%), suggesting its potential application for the synthesis of MMA and DMA.