Size effects on χ- to α-Al2O3 phase transformation

Catalytic Ethanol Dehydration to Ethylene over Nanocrystalline χ- and γ-Al₂O₃ Catalysts

“…Hexagonal χ-alumina seems to possess a layer structure. The arrangement of anions inherited from gibbsite, whereas the aluminum cations occupy octahedral sites within the hexagonal oxygen layer 28 .…”

Effect of Milling on the Formation of Nanocrystalline χ‐Al2O3 from Gibbsite

“…For the micrometer sizes, both transition routes (Fig. 1) may possibly occur, which depends on the heat treatment conditions 28 . The decomposition of boehmite would occur at 300°C at atmospheric pressure.…”

“…In general, reducing the particle size would lead to an increasing surface energy of the particle, thereby resulting in the decreasing of activation energy for phase transformation and transformation temperature as shown in the DTA profile 28 . The XRD patterns also confirmed that the transformation temperature of gibbsite to χ‐alumina reduced from 450° to 350°C after milling for 24 h. It may be attributed to the fact that gibbsite grows to the critical size of phase transformation and then transform to χ‐alumina at a lower temperature 28,31 . Moreover, the milling of gibbsite for 12 and 24 h can be up to 28% and 67% of the activation energy compared with that of the unmilled gibbsite.…”

Influencia del Ce en la hidrodesulfuración de tiofeno utilizando precursores catalíticos de heteropolioxomolibdatos de níquel tipo Anderson soportados sobre alúmina/Influence of Ce in the thiophene hydrodesulfurization using catalytic precursor of alumina

“…La γ-alúmina es uno de los materiales cerámicos mesoporosos más importante y ampliamente utilizado en HDS [10][11][12], debido a que posee alta área específica, sitios ácidos de Brönsted y Lewis, y excelente distribución de volumen y tamaño de poros [13][14][15][16][17][18][19]. Estudios recientes, han demostrado que por medio de la inserción de átomos como el cerio (Ce) en el soporte del catalizador modifica sus características fisicoquímicas, dando lugar a mejoras en las propiedades catalíticas (actividad, estabilidad térmica y tiempo vida útil) [20,21].…”