Abstract:

Pristine ETS-10 and AM-6 and their Co²⁺-exchanged forms were prepared, and their catalytic activities toward the oxidation of styrene in oxygen atmosphere were studied in dimethylformamide. The catalysts were denoted as Co-E10-n (n = 0, 9, 26, 68, 81) and Co-A6-m (m = 0, 8, 23, 63, 79), where n and m denote the degree of Co²⁺ exchange. The products of the oxidation process were identified as styrene epoxide (E) and benzaldehyde (B). Both the pristine forms, ETS-10 (Co-E10-0) and AM-6 (Co-A6-0), and Co²⁺-exchanged forms displayed catalytic activities. With increasing n or m, the conversion, and hence the rate, increased. Specifically, the rates varied from 6.1 to 12.5 mmol·g^-1·h^-1 with increasing n (Co-E10-n catalysts) and from 5.4 to 12.4 mmol·g^-1·h^-1 with increasing m (Co-A6-m catalysts). In contrast, the E/B ratio decreased with increasing n or m. More specifically, the E/B ratio decreased from 2.1 to 0.1 with increasing n from 0 to 81 (Co-E10-n catalysts) and from 1.3 to 0.1 with increasing m from 0 to 79 (Co-A6-m catalysts). Co-E10-9 displayed the highest E yield and Co-A6-79 generated the highest B yield. The highest turnover frequency obtained was 36.3 Co^-1·h^-1, which was the highest one obtained among those obtained for the Co²⁺-exchanged zeolites and mesoporous silica reference materials studied in this work.

Key words: Heterogeneous catalysis, Epoxidation, Cobalt, C=C activation, Zeolite