Synthesis of Pt/Al2O3 catalyst using mesoporous alumina prepared with a cationic surfactant

Abstract

Pt on alumina catalysts were studied when the texture of the alumina change by addition of a cationic surfactant cetyl-trimethyl ammonium bromide (CTAB). The mesoporous alumina was prepared using CTAB from 0.01 to 0.1M. The surface area and pore volume increased as CTAB concentration increased passing through a maximum. After calcination at 300°C, and 550°C boehmite and γ-Al2O3 were found by XRD. After calcination at 800°C, the transition between γ- and θ-Al2O3 was observed together with an increase of pore volume and pore diameter respect to the alumina without surfactant. The alumina prepared with the lowest concentration of CTAB showed the highest thermal stability. Brønsted and Lewis acidities were found on alumina samples having CTAB concentrations from 0 to 0.075M. The sample of alumina with the highest CTAB concentration showed the highest population of pentahedral aluminum (AlV), Lewis acidity and a dense network of wormlike particles by SEM. After H2 reduction of these catalysts, sulfur that came from the alumina support weakened the function of Pt particles to hydrogenolysis reaction whereas the CTAB introduced Brønsted acid sites in the alumina increasing the isomerization reaction.