Synthesis of nano-sized porous γ-alumina powder via a precipitation/digestion route Original Research Article

As a part of a study for the preparation of nano-sized γ-Al2O3 powder with controlled porosity and pore size distribution, a precipitation/digestion route was exploited to generate a boehmite precursor having a narrow size distribution of spherical nano-sized particles: size 3.5 nm with surface area ∼261 m2/g, average pore diameter of 4.86 nm, and pore volume ∼0.377 cm3/g. In this route, aqueous solution of aluminum nitrate and sodium carbonate were added simultaneously drop by drop to a well-stirred 200 ml volume of deionized water (taken in a round-bottom flask) at 70 °C to precipitate boehmite precursor in the pH range of 7.5–8.5 after digestion at the same temperature for 3 h. The boehmite precursor thus obtained is further washed with deionized water first to avoid ‘Na’ contamination and then by ethanol/acetone. The digested precipitate was finally air dried at room temperature. The calcinations of as-dried boehmite precursor at 550 °C/5 h in air produced porous nano-sized γ-Al2O3 powder particles having spherical shape with size of 4.5 nm. These powder particles showed BET surface surface area ∼220 m2/g with average pore diameter of 7.0 nm and pore volume ∼0.487 cm3/g. However, room temperature precipitation/digestion produces non-crystalline boehmite that gave poorly crystallized γ-Al2O3 powder particles with lower surface area ∼133.90 m2/g; these had higher average pore diameter of 26.67 nm with pore volume of 1.02 cm3/g. In methanol conversion to DME reaction, γ-Al2O3 catalyst made from precipitation/digestion at 70 °C gave a similar yield of DME when compared with the yield for γ-Al2O3 prepared from commercial Catapal-B boehmite sample.