Preparation Of TS-1 Containing New And Highly Active Sites For Propylene Epoxidation

Titanium silicalite-1(TS-1)is a milestone catalyst in zeolite catalysis due to its environmental friendly oxidation ability.Combined with hydrogen peroxide(H2O2),many processes including alkenes epoxidation,ketones ammoximation and aromatics hydroxylation are studied.Among them,hydroxylation of phenol,ammoximation of cyclohexanone,epoxidation of propylene and ammoxidation of methyl ethyl ketone are successfully commercialized.Epoxidation of propylene to produce propylene oxide is attractive in recent years and the key of this process is a high-performance TS-1 catalyst.To further enhance the catalytic performance of TS-1,extensive researches have been conducted on the understanding and controlling of Ti species,and decreasing particle sizes and creating hierarchical structures in TS-1.However,the effect of Ti species on the catalytic activity of the catalyst is not widely studied and true catalytically active Ti species in industrial TS-1 are often illusive.Therefore,further researches on Ti states and their effects on catalytic performance are studied by UV resonance Raman spectroscopy and it is significant to prepare high-perfromance TS-1.This thesis work develops methods to identify and quantify Ti species,and then quantify their catalytic activity in propylene epoxidation.Then it produces hierarchical TS-1 nanocrystalline catalysts containing only highly active Ti species.Finally,this work improves commercial TS-1 production process by consecutive use of mother liquor and implementing new discoveries mentioned before so as to enhance catalytic performance and decrease waste water.The research work has achieved the following main outcomes.UV resonance Raman spectroscopy and DFT calculations were used to identify new Ti species and their coordination structures in TS-1.In additional to the "TiO4",Ti-? and"TiO6" in TS-1,two new active Ti species including Ti-? and Ti-? were identified.The Ti-? was found to be most catalytically active among the five species and a new concept"active Ti species grouping" was proposed.Several Ti groupings exclusive for propylene epoxidation were created by hydrothermal modification of single active "TiO4" species.The catalytic activity of these groupings was found to be higher than the single "TiO4" species and followed the order of{Ti-?+Ti-?+Ti-?}>{"TiO4"+Ti-?}>{Ti-?+Ti-?+"TiO6"}>{Ti-?+Ti-?}.Hierarchical H-S-1@TS-1 and 3M-TS-1(ML)containing TS-1 nanocrystallines were hydrothermally prepared without the need of multiple structure-directing agents.Their pore structures and Ti states were determined by the sequence of hydrothermal synthesis and hydrothermal modification.H-S-1@TS-1 contained hollow structure with single active"TiO4" species whereas 3M-TS-1(ML)contained macro-meso-micro structure with sole{Ti-?+Ti-?+Ti-?} grouping.They exhibited good catalytic performance and 3M-TS-1(ML)delivered superior propylene oxide yield than the current industrial TS-1 of 6.2 percentage points.Our commercial process to produce industrial TS-1 was improved by application of mother liquor in TS-1 synthesis and post-treatment.As a result,high-perfromance TS-1 catalysts were prepared and generation amount of waste water was dramatically decreased.The propylene oxide yield of new TS-1 catalysts increased by 18.0-25.6 percentage points than industrial TS-1 because their active Ti groupings were {Ti-?+Ti-?+Ti-?},but the active Ti grouping in our industrial TS-1 was {Ti-?+Ti-?}.