One-pot synthesis of novel hierarchical bifunctional Ga/HZSM-5 nanosheets for propane aromatization

Abstract

Hierarchical galloaluminosilicate nanosheets with the MFI structure have been successfully prepared by a one-pot hydrothermal process. Tetrabutylphosphonium hydroxide (TBPOH), a dual structure-directing agent (SDA), was used to simultaneously produce the MFI structure and the self-assemblies of nanolayers. The as-synthesized samples were characterized by means of XRD, TEM, SEM, EDS, ICP, ²⁷Al MAS NMR, H₂-TPR, NH₃-TPD and N₂ physisorption. The galloaluminosilicate nanosheets exhibit outstanding properties, such as an extremely high meso/macroporosity (one to two orders of magnitude higher compared with the conventional zeolite), a uniform Si, Al and Ga distribution, along with the appropriate acidic properties. The galloaluminosilicate nanosheets can greatly enhance the catalytic performances in terms of activity (60 and 20% for propane conversion over the hierarchical Ga/HZSM-5 and the conventional zeolite, respectively), BTX selectivity (almost three times higher compared with the conventional zeolite), and significant reduction of deposited coke (approximately by 70%) for conversion of propane at 823 K under atmospheric pressure without any special pretreatments of catalysts. This first example demonstrates a simple and low-cost approach for the synthesis of hierarchical bifunctional zeolite nanosheets and the challenge for the development of heterogeneous catalysts.