Effect of the Nano Size of the Particles on the Porous Structure of Alumina and its Role in Dehydrogenation Reactions

The present work aims at optimizing the nano size of the particles of γ-alumina to generate micro- and meso-porous structures and improve the efficiency of dehydrogenation catalysts. Following this trend, two different kinds of γ-alumina were prepared using low and high concentration of cetyl tri-methyl ammonium bromide surfactant (CTAB). Both kinds of alumina were characterized by XRD, TG, DTA, SEM and TEM in addition to surface characterization. SEM and TEM images showed that the alumina prepared with the low concentration of CTAB has groups of ultra fine nanoparticles with size ∼ 7 nm assembled into a strong agglomeration with creating micro- and meso-porous structures and high surface area (256.9 m2/g). With the high concentration of CTAB, the nano size of alumina increased to become ∼100 nm creating only meso-porous structure. These results indicated that the spherical particles of alumina with the nano size below 10 nm adhere to two or three other particles creating the cavities between the globules and providing micro- and mesoporous structures. On the other hand, the aggregates of the nanoparticles above 10 nm produce only mesoporous structures. Our results conclude that the size of the globules determines the specific surface area of the solids, its pore volume and the diameters of its pores. Development of the dehydrogenation catalyst was achieved by supporting 0.6 wt.% platinum metal over the micro-and mesoporous structure of the prepared γ-alumina. The results of catalytic activity concluded that the prepared nanocatalyst is selective toward cyclohexane dehydrogenation reaction with catalytic conversion of cyclohexane 87% at 450 °C.