Effect of the laser-synthesized γ-Al2O3 support on the activity of Fe/γ-Al2O3 nanopowders in dehydrogenation of isobutane

Abstract

The study shows that two types of the γ-Al2O3 supports synthesized using laser vaporization and precipitation methods essentially differ in their morphology and pore structure. The first type of support is represented by weakly agglomerated spherical particles with the diameter of 3–10 nm, whereas the second type consists of strongly aggregated and disordered nanocrystallites with the diameter of 10–15 nm. The indicated supports were used to obtain Fe/γ-Al2O3 catalysts with different Fe content by incipient wetness impregnation. In the catalyst supported on the laser-synthesized γ-Al2O3, the pore size distribution is narrow and pore sizes are close to the particle sizes. HAADF-STEM made it possible to observe highly dispersed locally isolated regions of iron oxide with the size of 0.5–2.0 nm in the maghemite (γ-Fe2O3) phase, which are not detected by XRD. On the contrary, according to XRD, the deposition of iron on the γ-Al2O3 obtained by precipitation leads to the distinct hematite (α-Fe2O3) phase with the crystallite size of ∼33 nm. Distinctive features of the catalysts were found also by H2-TPR and NH3-TPD. Comparative testing of the catalysts with the iron content of 5.0 wt.% revealed that the system obtained using the γ-Al2O3 synthesized by laser vaporization is by 6–10% more active in the fixed-bed dehydrogenation of isobutane.