[Title] Synthesis and characterization of composites of MgAl-Based layered double hydroxide and Nb oxide clusters
[Authors] H. Kawasoko, K. Takahashi, S. Hongpuek, S. Kikkawa, S. Yamazoe
[Journal] J. Jpn. Petrol. Inst. accepted.
[Abstract] Polyoxometalates (POMs), called as metal oxide clusters, show unique properties including superacidity and superbasicity. Among them, Nb- and Ta-based POMs have attracted attention as homogeneous catalysts due to their water-resistant superbasicity and catalytic activity in CO2 fixation. To utilize these POMs as solid base catalysts, compositing of POMs with layered double hydroxides (LDHs) is a promising approach. In this study, composites of Lindqvist-type [Nb6O19]8− (Nb6) and MgAl-based LDH were synthesized using the reconstruction method. Various structural analysis confirmed the successful intercalation of Nb6 into the LDH while Nb6 maintained its Lindqvist-type structure. X-ray diffraction showed an increased interlayer distance consistent with the size of Nb6, and energy dispersive X-ray spectroscopy confirmed the high dispersion of the Nb6 within the LDH. Knoevenagel condensation reaction showed that the Nb6-LDH composite achieved yields of 33% and 30% for substrates with pKa of 19.5 and 21.9, respectively, which was significantly higher than bare LDH without Nb6 (3%), indicating that Nb6 retains its basic catalytic activity after intercalation. These results suggest the Nb6-LDH is a promising solid base catalyst.