Saminda Dharmarathna

Ordered mesoporous mixed metal oxides: remarkable effect of pore size on catalytic activity.

We report the synthesis of ordered mesoporous NiAl mixed metal oxides (MMOs) from NiAl-layered double hydroxides (LDHs) through a soft template method using pluronic-F127 as the structure-directing agent. Ordered mesopores were obtained by the thermal decomposition of as-synthesized LDHs at different temperatures. The effects of the pluronic-F127 amount and the calcination temperature on the pore size distribution of the MMO were investigated. NiAl MMOs exhibited excellent catalytic activity in the Knoevenagel condensation of benzaldehyde with acidic methylene group-containing malononitrile. Finally, the dependence of the catalytic activity on the surface properties of NiAl MMOs was investigated. The pore diameter and the pore volume of NiAl MMOs were well correlated with the performance of the catalysts. MMO obtained from the calcination of NiAl-F127(3%)LDH at 750 °C for 5 h gave the highest conversion (>99%) in the Knoevenagel condensation in 30 min. The optimum pore diameter for the model reaction described here was 7.7 nm, which gave rise to more than 99% conversion with 100% selectivity. Ethanol gave the best conversion at 60 °C. The regenerated catalyst showed 93.0 and 89.0% of the initial catalytic activity after the first and the second regeneration cycles, respectively.

Bimodification of Mesoporous Silicon Oxide by Coupled “In Situ Oxidation at the Interface and Ion Exchange” and its Catalytic Activity in the Gas-Phase Toluene Oxidation

A bimodification synthesis method—“in situ oxidation at the interface (IOI) coupled with an ion exchange”—has been developed for the internal surface modification of mesoporous silicon oxide (MPS) templates. First, manganese oxide was formed at the internal surface of the MPS template through IOI. In the IOI method, high‐valent oxo‐anions of manganese (MnO4−) were used for the selective oxidation of poly(ethylene oxide) (PEO) groups of the Pluronic P123 (PEO20PPO70PEO20; PPO=poly(propylene oxide)) surfactant and they formed manganese oxide at the organic–inorganic (corona) interface. The oxide formation was restricted at the corona interface by a positively charged CTA+ (cetyltrimethylammonium) head group of the cationic surfactant CTABr. Then, the second modification of the MPS template was also performed by introducing promoter cations (Cs+, K+, or H+) through an ion exchange reaction between the cations and CTA+. The bimodified MPSMnX (X=Cs, K, or H) samples preserved the mesoporosity and high surface area of the MPS template. The bimodified MPSMnX samples were found to be more active, selective, and stable than the singly modified MPSMn sample for the gas‐phase oxidation of toluene.