Synthesis of mesoporous alumina nanoparticle using agarose template for lewis acid catalyst

Abstract

Porous alumina with high surface areas and narrow pore size distribution has wide applications in catalysis, catalyst support, molecular separation and adsorbents. In this study, agarose gel having porous structure was used as template in the preparation of mesoporous alumina. This method was introduced in order to provide an alternative method to design the pore structure of metal oxide having nanosized grains. Four different amount of agarose gel template were used to synthesize this material, i.e. 0.5 wt%, 1.0 wt%, 2.0 wt% and 4.0 wt%. The agarose gel was coated with aluminium isopropoxide precursor. The XRD and FTIR results showed that the alumina has ?-phase structure. The alumina obtained from 2 wt% and 4 wt% of agarose gel template exhibits uniform mesopores alumina and the surface properties analyzed using nitrogen adsorption-desorption showed narrowest pore size distribution centered at 7.2 nm with the highest surface area obtained was 308 m2/g. The SEM images of agarose showed sponge-like pore structure while FESEM revealed that the size of granule-like nanoparticles mesoporous alumina decreased by increasing amount of agarose template. TEM proved that the mesoporous alumina particle was successfully obtained with rod-like morphology with average length of 5-7 nm. Lewis Acid site present in mesoporous alumina was confirmed by pyridine- FTIR and catalytic activity of alumina was evaluated in Knoevenagel condensation reaction of benzaldehyde with methyl cyanoacetate and dimethyl malonate separately. The percentage conversion of each reaction was 54% and 47%, respectively compared to uncatalyzed reaction which was 4.0% and 18%, respectively. The low conversion of dimethyl malonate was due to the bulky molecule product entrapped in the pore of alumina surface. The results obtained showed that synthesized mesoporous alumina is capable to catalyze Knoevenagel condensation reaction.