A facile synthesis strategy for structural property control of mesoporous alumina and its effect on catalysis for biodiesel production

Abstract

A facile synthesis route for the production of mesoporous alumina (MA) with tuneable structural properties including BET surface area, pore volume and pore size was systematically investigated by tailoring the amount of template P123 used in the synthesis. The general synthesis strategy was based on a sol–gel process by hydrolysis of aluminium isopropoxide associated with nonionic block copolymer (P123) as the template in a water system. The results showed that the addition of P123 played a crucial role in the synthesis process, leading to very regular variations in the surface area (146.6–261.6m2/g), pore volume (0.164–2.152cm3/g) and pore size (3.5–29.9nm). MA-supported K species (MA-K) were prepared using KNO3 as the potassium precursor and adopted as the catalysts for biodiesel production. The introduction of K species to MA caused a reduction in the BET surface area and pore volume, but gave rise to a significant increase in pore size, especially when the K species was higher than 10%. K incorporation resulted in the formation of disordered, but significantly larger mesopores. In catalysis, by introducing 20% molar fraction of K species to MA, very high yield of biodiesel was achieved (92.2%) and further increased to 94.4% with 25% K. Based on the control of structural properties of MA, a series of MA-20K catalysts with the same K loading (20%) but different structural properties were prepared by varying P123 addition and were further tested in biodiesel synthesis. Higher biodiesel yields were obtained over the MAs with higher surface area, pore volume and bigger pore size, which were attributed to the reduced mass transfer limitation in catalysis.