Physicochemical and Catalytic Properties of Sol−Gel Aluminas Aged under Hydrothermal Conditions

Abstract

Sol-gel boehmite was aged under hydrothermal conditions at 200 °C using water as mineralizer agent. Samples were characterized with X-ray powder diffraction, nitrogen adsorption, and transmission electron microscopy. Calcined solids were also studied by infrared spectroscopy of adsorbed pyridine. Their catalytic properties were determined in the 2-propanol decomposition. The hydrothermal treatment ordered the atoms of the sol-gel boehmite mainly in two dimensions forming thin crystallites, which grew as treatment time increased. Due to the pseudomorphic transformation of boehmite into γ-alumina, the arrangement of crystallites in the corresponding boehmite determined alumina particle morphology and porosity. The pore size distribution was narrow, and the pore size shifted to larger values as the time of hydrothermal treatment increased. The strength and number of acid sites depended also on the treatment time. The catalytic activity correlated well with the acidity and specific surface area.

Fractal Geometry Approach to Describe Mesostructured Boehmite and Gamma‐Alumina Nanorods

“…The hysteresis loop for the APECl [boehmite prepared with ethanol (E) and hydrochloric acid (Cl)] and APEClC [alumina prepared with ethanol (E) and hydrochloric acid (Cl), calcined (C) after drying] samples are of the H2 type, [44] which is in agreement with randomly folded boehmite sheets of solids. [45] But in the other samples {APES, APPS [boehmite prepared with 2-propanol (P) and sulfuric acid (S)], APBS [boehmite prepared with 2-butanol (B) and sulfuric acid (S)], APESC [alumina prepared with ethanol (E) and sulfuric acid (S), calcined (C) after drying], APPSC, and APBSC}, the hysteresis loops are of type H1, which is in agreement with uniformly folded boehmite sheets of solids, a homogeneous pore-size distribution, and a uniform particle size. Pore size plots of boehmite and alumina samples (Figures 4b and 5b) show that they are narrowly distributed.…”

Improving textural properties of γ-alumina by using second generation biomass in conventional hydrothermal method

“…The stacking of g-alumina matrix could be related to oxygen sub-lattice from boehmite. The arrangement of crystallites into corresponding boehmite determines g-alumina morphology and porosity due to the pseudomorphic transformation of one phase into another [16]. Transitions alumina (up to a-alumina) undergo meta-stable transformations [17] in both crystal self-assembly processes during pre-synthesized colloidal solegel system and during thermal treatment.…”

Tailoring Porosity of Colloidal Boehmite Sol by Controlling Crystallite Size

“…Although the considerable efforts for the preparation of boehmite have been carried out using the sol-gel reaction, there is still a need for further studies to exert the control of physical properties of boehmite colloidal sols. 22,23 Therefore, how to manipulate the crystallite size and control the porosity is an important issue for the preparation of boehmite in a stable colloidal solution.…”