Control of surface acidity and catalytic activity of γ-Al2O3 by adjusting the nanocrystalline contact interface

Grain boundaries in nanocrystalline catalytic materials as a source of surface chemical functionality

“…This was confirmed by 27 Al solid state NMR spectra ( Figure 16B) indicating a strong increase of the concentration of tetrahedral aluminum ions (peaks at 68.7-68.9 ppm) and shifting their center position (inset in Figure 16B) reflecting increased distortion in GB areas. A strong increase of Lewis acidity of γ-Al 2 O 3 after densification was confirmed by FTIR spectra of chemisorbed pyridine and NH 3 -TPD spectra (Vidruk et al 2011). The γ-Al 2 O 3 materials with different consolidation degree of nanocrystals having a similar size were tested in dehydration of iso-propanol at 523 K. Increasing θ from 1.7 to 3.3 increased the reaction rate per surface area by a factor of 4.4 (Vidruk et al 2011).…”

“…Increasing of consolidation degree of primary nanocrystals in γ-Al 2 O 3 aerogel due to thermal densification at 1073 K increased the specific surface acidity (A) measured by indicator titration by a factor of 7 where θ increased from 1.7 to 3.3 ( Figure 16A) (Vidruk et al 2011). The typical S-shaped curve may be explained by accelerated formation of novel acid sites on the surface at higher θ values.…”

“…The approach was successfully applied to magnesia aerogel where three consecutive fillings of meso-macropores with MgO nanocrystalls increased θ from 1.3 to 1.5÷3.5 at crystal size of 5 nm. Filling the pores of γ-alumina aerogel with additional γ-Al 2 O 3 nanocrystals increased θ from 1.7 to 3.1 and the crystal size from 2 to 4 nm after 2 h calcination at 1073 K (Vidruk et al 2011).…”

“…This can be done for materials with relatively low rate of surface diffusion of ions, reducing sintering and crystal growth like in metal oxides (mixed oxides) (Chaim et al 2008, Fang andWang 2008). The thermal densification was successfully applied to γ-alumina aerogel with primary crystal size of 2 nm (Vidruk et al 2011). Prolonged thermal treatment at 1073 K for periods 2, 6, 10 and 14 h reduced the nanocrystal aggregates and micropore volume/surface area due to reduction of slit-shaped voids between nanocrystals (Figure 8).…”

Gas-phase dehydration of glycerol over commercial Pt/γ-Al2O3 catalysts

“…phase. This oxy-hydroxide phase AlO(OH) commonly termed as pseudoboehmite is generally the precursor to γ-Al 2 O 3 phase and completely conversts to the alumina phase at higher temperatures [60,61]. X-ray diffraction pattern of the used AP-64 catalyst sample is very similar…”