Heterogeneous strong base catalysis in supercritical carbon dioxide by mesoporous alumina and sulfated mesoporous alumina

Abstract

The development of solid strong base catalysts utilizable in green but acidic medium of scCO 2 is reviewed. The strong base sites on mesoporous alumina and sulfated mesoporous alumina that had been generated by severe treatment at 773 K under vacuum (10 )4 Torr) were not neutralized by the compressed Lewis acidic molecules of CO 2 , promoting a representative strong basecatalyzed reaction of the Tishchenko reaction as well as a typical base-catalyzed reaction of the Knoevenagel reaction in scCO 2 . Infrared spectroscopy of the adsorbed pyrrole, temperature-programmed desorption of CO 2 , and the poisoning by a very weak Bro¨nsted acid of methanol have revealed that the average strengths of the base sites on mesoporous alumina and sulfated mesoporous alumina are weaker than that on conventional c-alumina like JRC-ALO-4, but that they have a small number of strong base sites which function even in scCO 2 medium. It was found that the addition of a slight amount of THF cosolvent into scCO 2 remarkably accelerates the Tishchenko reaction over sulfated mesoporous alumina; the reaction rate in the scCO 2 -THF medium was 1.5-fold and 2-fold faster than those in ordinary organic solvents such as benzene and THF and that in pure scCO 2 , respectively. The unique structures of mesoporous alumina and sulfated mesoporous alumina have been fully characterized by N 2 adsorption-desorption measurements and XRD analyses.

Design and fabrication of mesoporous heterogeneous basic catalysts

“…251 Although MgO could yield the Knoevenagel product under solvent-free conditions, the yield did not increase after supercritical CO 2 was introduced. Normally, the Knoevenagel reactions are performed under solvent-free conditions or in traditional organic View Article Online solvents such as toluene and methanol, while acidic supercritical CO 2 medium was used.…”

“…251 Non-mesoporous g-Al 2 O 3 and MgO were also employed for comparison. Basicity of pure mesoporous alumina.…”

Synthesis, Characterization and Catalytic Applications of Organized Mesoporous Aluminas

“…These results on preparation, characterization and catalytic testing of base catalysts originating from organized mesoporous aluminas were reviewed in ref. (117). properties with respect to catalytic data but it is more than evident that further and deep investigations are needed.…”

Poly(ethylene oxide)–Poly(butylene oxide)–Poly(ethylene oxide)-Templated Synthesis of Mesoporous Alumina: Effect of Triblock Copolymer and Acid Concentration

“…Alumina is commonly used in a variety of applications such as catalysis, − optical and biomedical purposes, ceramics, , and adsorption. − The addition of supplementary metal oxides, such as titania (used extensively in catalysis and photocatalysis , ), brings further applications to these materials. Titania-alumina materials can be used in automotives and aeronautics, dental implants and orthopedics, and the decontamination of chemical warfare agents .…”