Functional mother liquor reversed titanium species for the green synthesis of anatase-free hollow TS-1 with tunable titanium micro-environment via a kinetic-thermodynamic co-regulatory pathway

Abstract

Realizing anatase-free hollow TS-1 with a controllable titanium micro-environment via dissolution-recrystallization for diverse catalytic reactions remains a great challenge due to the insufficient comprehension of dissolution-recrystallization mechanism, high cost and environmental issues. Here, anatase-free hollow TS-1 was economically synthesized via mother-liquor-induced dissolution-recrystallization, realizing the controllable micro-environment and spatial distribution of titanium. A novel kinetic-thermodynamic co-regulatory pathway was unveiled for the first time to describe the magical reversible varying of titanium micro-environment during the dissolution-recrystallization process (dissolution-reinsertion-secondary dissolution). Thermodynamically, temperature and liquid-to-solid ratio cause the formation of anatase and unsaturated silicon, and the unsaturated silicon species (Q¹ and Q²) determine the subsequent capture and re-insertion of anatase. Original unsaturated silicon species in the mother liquor endow it with a unique function to further facilitate the elimination of anatase. Kinetically, temperature determines the dynamic progress of the reversible process such as evolution speed and deposition priority of titanium and silicon species. Multi-factor dynamic constraints directly determine the micro-environment, spatial distribution and content of titanium. This provides a new perspective for predicting and synthesizing hollow heteroatomic zeolites with ideal heteroatom micro-environments. Unique surface properties and diverse titanium micro-environments endow hollow TS-1 with superior mass-transfer abilities to exhibit different activities in 1-hexene epoxidation and phenol hydroxylation.