From Al-SBA-15 to Ga-SBA-15: Morphology and acidity evolution in the acid-free synthesis

Tuning the morphological and acidic properties of mesoporous molecular sieve materials is highly valuable for catalyst design towards the reactions involving large molecules. In this work, a series of Ga-containing SBA-15 ordered mesoporous materials (OMMs) were synthesized following the acid-free strategy. Ga-SBA-15 exhibits an acid amount of 0.48 mmol/g, comparable to the Al-SBA-15 (0.45 mmol/g). In addition, it is found that the straight short stick particles of Al-SBA-15 integrally bended upon a replacement of Al with Ga and the tendency continuous with the incremental addition of gallium, until fully transforms into the highly dispersed isolated bending particles of Ga-SBA-15. Owing to the improved interparticle-type mesoporosity derived from the dispersed bending particles, the active sites on external surface are highly accessible for large molecules. As for the acidic property, the Brönsted-type acidic property of Al-SBA-15 changed to the Lewis-type acidity with the replacement of gallium. In the Ga-SBA-15 case, more than 93% of strong acid sites were confirmed as Lewis characteristic. On the other hand, Low Density Polyethylene (LDPE) exhibits a faster decomposition rate over Ga-SBA-15 than Al-SBA-15 and Al–Ga bimetallic doped SBA-15 (galloaluminosilicate) catalysts. • Ga-containing SBA-15 mesoporous materials were synthesized following the acid-free strategy. • Replacement of Al with Ga induces a morphological evolution from the straight short stick to a bending shape. • Ga-SBA-15 exhibits strong Lewis acidity and hierarchical pore structure solely composed of interparticle-type mesopores.