Silica waste with different surface properties for solvent-free synthesis of TS-1 and its efficient epoxidation of chloropropene

Utilizing silica-rich wastes for synthesis of zeolite can realize a green production protocol and make best use of solid waste. However, industrial solid wastes usually require a complicated pretreatment process and their surface properties are underestimated for the final products. In this study, silica wastes with different acid or basic surface properties are directly used for the solvent-free synthesis of TS-1 zeolites. The states of Ti species, Si/Ti molar ratios, and morphology of final TS-1 zeolites can be controlled by the pristine surface properties and additional ammonium carbonate. TS-1 zeolite synthesized from acid silica waste exhibits lower crystallinity, abundant highly coordinating titanium species, and an elongated c-axis compared to that from basic silica waste. More importantly, TS-1 zeolite (nSi/nTi=30) synthesized from silica with acid property possesses excellent performance in the epoxidation of chloropropene with 66.2% conversion and 98.5% selectivity to epichlorohydrin, which is attributed to the presence of abundant high-coordination Ti species of mononuclear TiO6. Our strategy provides a novel idea for totally green synthesis of zeolite by utilizing solid wastes.