钛硅分子筛固定床催化环己酮肟的绿色合成

Three representative extruded titanosilicate catalysts, Ti-MOR, TS-1 and Ti-MWW, were prepared from corresponding titanosilicate powders by adding a pore-forming agent (sesbania powder), 30 wt.% alkaline silica sol as a binder, and water. The performance of the ground powder catalysts in the liquid-phase ammoximation of cyclohexanone in a batch reactor was first investigated, giving the order of catalytic activity of Ti-MOR > TS-1 > Ti-MWW. The extruded catalysts were then used in a green process to produce cyclohexanone oxime in a fixed-bed reactor with hydrogen peroxide as the oxidant. When the ammoximation was performed in the fixed-bed reactor, where the products and catalyst were easily separated, Ti-MOR proved to be more efficient than conventional TS-1 and Ti-MWW, consistent with the results obtained for the batch reaction. The reaction parameters for the shaped Ti-MOR catalyst in a continuous fixed-bed reactor were then optimized systematically. Ti-MOR gave a cyclohexanone conversion of >95% and oxime selectivity of >99% under the optimized reaction conditions. The lifetime of the shaped Ti-MOR catalyst in the ammoximation of cyclohexanone in the continuous fixed-bed reactor reached 360 h while maintaining a cyclohexanone conversion of over 95%, oxime selectivity exceeding 99%, and residue of unconverted H₂O₂ of about 3%. Catalyst deactivation was elucidated to be caused by coke deposition and partial loss of Ti active sites. The deactivated Ti-MOR catalyst was regenerated effectively by removing the organic species occluded within the zeolite pores by air calcination at 823 K. The catalytic activity of the regenerated Ti-MOR was about 80% that of the fresh one, but it still provided an oxime selectivity of >99%.