Synthesis of stable H-galloaluminosilicate MFI with hierarchical pore architecture by surfactant-mediated base hydrolysis, and their application in propane aromatization

The role of ordered hierarchical pore arrangements of H- galloaluminosilicate in the aromatization of propane was investigated. Stable ordered mesoporous H-galloaluminosilicate was formed via surfactant-mediated base hydrolysis of steamed H-galloaluminosilicate. It was observed that the resulting H-galloaluminosilicate with mesoporous/microporous hierarchical structure exhibited superior aromatization performance and stability, as compared with steamed H-galloaluminosilicate. The results showed that there were strong correlations between mesoporosity, distribution and dispersion of Ga species, Bronsted-Lewis acidity, and propane aromatization. The optimal ordered mesoporous (hierarchical) H-galloaluminosilicate zeolite (treated in 0.40 M NaOH in the presence of CTAB) had a mesopore surface area of 107 m²/g, highly dispersed-reducible Ga species, and preserved intrinsic zeolitic properties. This sample displayed remarkable catalytic performance in propane aromatization, with conversion of 56.3%, as compared to 30.8% provided by steamed H-galloaluminosilicate. At comparable conversion level (∼25%), the ordered mesoporous H-galloaluminosilicate was more selective to aromatics (BTX), with 58.3% as compared to 42.5% for conventional sample. The superior aromatization performance was tentatively attributed to the (gallination- degalliation-"re-gallination" of extracrystalline Ga₂O ₃) effect promoted by the combined effects of hydrothermal (in situ) synthesis and hierarchal pore arrangements. On the contrast, propane aromatization ability of HZSM-5 catalysts was not changed upon the hydrolysis under analogous hydrolytic conditions as those of H-galloaluminosilicate.