Effect Of Na~+in Synthesis Of Titanium Silicalite-1on Its Catalytic Performance In Cyclohexanone Ammoximation And Regeneration Of Deactivated Catalyst

Titanium silicalite-1(TS-1) catalyzed ammoximation of cyclohexanone withH2O2to cyclohexanone oxime can be carried out under mild conditions with highconversion and high selectivity, which is an environmentally friendly process. It hasbeen intensively studied in recent years. This process has the potentiality to replacethe traditional processes to become the main technology for the cyclohexanone oximeproduction.In this work, TS-1was synthesized by using tetrapropylammonium hydroxide(TPAOH) as template and tetrabutyorthotitanate (TBOT) and tetraethylorthosilicate(TEOS) as Ti and Si sources, respectively. The effects of sodium ions in the synthesisof TS-1on the catalytic properties in the ammoximation of cyclohexanone wereinvestigated in a continuous slurry-bed reactor. The experimental results indicated thatthe addition of Na+below3molar percentage of TPAOH in the synthesis did notinfluence the catalytic properties. The catalyst shows a stability of16h on streamunder drastic conditions. However, when the addition of Na+in the synthesis increasesto3molar percentage of TPAOH, the catalyst life is shortened to12h. And thecatalytic stability decreases further when the concentrations of Na+was increased inthe synthesis. In order to investigate the effects of sodium ions in the synthesis ofTS-1on the catalytic properties, TS-1synthesized with different concentrations ofNa+were characterized by XRD, SEM, XPS, ICP, FT-IR, UV-Vis and TGA. Theresults suggested that the framework structure of samples was not destroyed, but withthe increase of Na+concentrations, the crystal sizes of TS-1increased, extraframework Ti increased, while the framework Ti decreased. So the effects of Na+canbe attributed to the increase of TS-1crystal sizes, the decrease of the frameworktitanium and the increase of extra framework titanium. In the synthesis of the catalystsfor the cyclohexanone ammoximation, Na+should be kept at below3mol.%relativeto TPAOH.The regeneration of the deactivated TS-1in the cyclohexanone ammoximationwas also studied. The fresh, deactivated and regenerated catalysts were characterizedby XRD, FT-IR and TGA. The results suggested that the catalyst deactivation was notdue to the collapse of the zeolite framework or the loss of titanium from the framework. The main reason was the blockage of the channels of the catalyst bybulky organic compounds formed by cyclohexanone oxime and by-products, whichcovered the active centers of titanium in the catalyst. Then, the selectivity tocyclohexanone oxime decreased and catalyst deactivated. The deposited materials onthe deactivated catalyst can be effectly removed by treatment with H2O2/HNO3solution at high temperatures, and the higher the regeneration temperature and thehigher the H2O2concentrations in methanol were, the better the revovery of thecatalyst activity was.