Metal-containing molecular sieves as catalysts for the selective oxidation of cyclohexane by oxygen

Abstract

Three types of metal-containing molecular sieves with AFI, AEL and CHA structures were hydrothermally synthesized. Metals (Co, Mn, Cr, V) were incorporated into the molecular sieve framework and induced the appearance of charge centres, as evidenced by TG and NH 3 -TPD. TPR studies revealed that cobalt and manganese in the framework were not reducible before the collapse of molecular sieve structure. The catalytic behaviours of these catalysts in cyclohexane oxidation at 403 K and 1.1 MPa O 2 were investigated. CoAPO-11 exhibited best activity and good selectivity of monofunctional oxidation products (88.5%). Cyclohexanol was the preferable product on most catalysts, whereas for CrAPO-5, -11, high selectivity of cyclohexanone was observed. Experimental results indicated that the decomposition of cyclohexyl hydroperoxide (CHHP), the intermediate in cyclohexane oxidation, followed the pathway: cyclohexanone←CHHP→cyclohexanol (then cyclohexanol→cyclohexanone).