Abstract
Hollow silica nanospheres with ultra-high acid density were fabricated successfully via sulfonation of phenyl-functionalized hollow silica nanospheres, which were synthesized through a single micelle (F127 (EO106PO70EO106))-templated method, with phenyltrimethoxysilane and tetramethoxysilane (TMOS) as silane precursors under neutral conditions. The density of sulfonic acid reached as high as 1.97 mmol/g. The characterization results of 31P-NMR using triethylphosphine oxide as a probe molecule suggested that the acid strength of hybrid solid acids could be systematically tuned by tuning the content of sulfonic acid and higher acid density results in stronger acid strength. Attributed to the unique hollow structure and high-acid density, the sulfonic acid-functionalized hollow silica nanospheres exhibited good catalytic performance in the condensation reaction of benzaldehyde with ethylene glycol. Notably, this study found that the catalytic activity was significantly influenced by the acid density and the ultra-high acid loading was beneficial for the activity due to the enhanced acid strength. This novel solid-acid catalyst also showed good recyclability and could be reused for at least 11 runs.
Highlights
Replacing hazardous and corrosive mineral liquid acids with solid acids is meaningful for the industrial production of fine chemicals with environmental and safety considerations [1,2,3,4]
We report the construction of hollow silica nanospheres with ultra-high acid loading (1.97 mmol/g, denoted as SO3 H-Ph-HNS-x) via sulfonation of phenyl-functionalized hollow silica nanospheres, which were fabricated by a one-pot hydrothermal method with phenyltrimethoxysilane and tetramethoxysilane (TMOS) as precursors (x is the mass ratio of added phenyltrimethoxysilane with TMOS) and F127 (EO106 PO70 EO106 ) as a single micelle template under neutral conditions
The solid-acid catalyst SO3 H-Ph-HNS-x was obtained by sulfonation of phenyl-functionalized hollow nanospheres with a commonly used chlorosulfonic acid
Summary
Replacing hazardous and corrosive mineral liquid acids with solid acids is meaningful for the industrial production of fine chemicals with environmental and safety considerations [1,2,3,4]. [5,6,7,8,9,10,11,12,13,14] Among these solid acid catalysts, sulfonic acid-functionalized mesoporous silica have attracted much research interest owing to their superior advantages, such as high surface area and pore volume, large pore size, and good thermal stability [15,16,17,18,19,20]. These features make them promising alternatives to commercial sulfonated polymer resins (like Amberlyst-15, Nafion-H) which suffer from the drawbacks of low surface area. Systematic study of the relationship of the acid loading, acid strength, and catalytic performance was conducted
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