Epoxidation of 1-octene under harsh tail-end conditions in a flow reactor II: impact of delaminated-zeolite catalyst surface area and structural integrity on catalytic performance†
Building on our previous study of delaminated-zeolite catalysts for harsh tail-end conditions in an epoxidation flow reactor employing organic hydroperoxide as oxidant, this manuscript compares approaches for delamination in catalyst prepration. In one, a mild method of delamination is used for synthesis of Ti-UCB-4, in which fluoride in organic solvent is used as a mineralizing agent to affect delamination, while in another, catalyst Ti-SSZ-70-DEL-HIGHPH is synthesized by delamination under high-pH conditions and results in the highest external surface area, similar to that previously reported for ITQ-2. We also compare both materials to the calcined 3-D zeolite consisting of Ti-SSZ-70, a control which underwent no delamination treatment. Results of long-term flow reactor catalytic testing demonstrate a distinct 2.5-fold increase in reaction-rate constant k′ on a mass basis for Ti-UCB-4 relative to 3-D Ti-SSZ-70, and a lack of long-term deactivation for both catalysts. In contrast, for Ti-SSZ-70-DEL-HIGHPH, due to deactivation, no steady-state behavior is observed for either conversion or selectivity with increasing times on stream. A combination of data from powder X-ray diffraction (PXRD), nitrogen physisorption at 77 K, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and UV-visible (UV-vis) spectroscopy demonstrate Ti-SSZ-70-DEL-HIGHPH to be comprised of a combination of crystalline and amorphous phases. Control experiments demonstrate a negative synergy on catalysis when both phases are combined in a single catalyst, which leads to decreased conversion, at levels below values predicted based on the linear combination of the two phases present.