Behaviour of Amorphous Aluminosilicates towards Ageing by High‐Temperature Steaming

Abstract

The structure of amorphous aluminosilicates obtained by grafting silicon on alumina (Si/Al2O3) mostly remains the same after ageing by steaming. The rearrangement of surface silicon species on the facets of γ‐alumina slightly decreases the number of Brønsted acid sites, which is determined through ethanol adsorption followed by thermogravimetry as well as m‐xylene isomerisation. Al/SiO2 prepared by grafting aluminium on silica undergoes sintering of the silica support and the agglomeration of the surface aluminium species during steaming. This process leads to a sharp decrease in the number of Brønsted acid sites, which are associated with the dispersed aluminium species, and dehydroxylation of the silica surface.

Comment on: “Brønsted acidity of H-MCM-22 as probed by variable-temperature infrared spectroscopy of adsorbed CO and N2” by Delgado et al. [Catal. Today 227 (2014) 45–49]

“…Such hypothesis is conceivable as presence of Al(OH) hydroxyls reveal a weak dealumination of the H-MCM-22 zeolite. As previously demonstrated, ASA have Brønsted acidic strength covering a large range of values that may explain the broadness of the OH· · ·CO overlapping band [14,17,[27][28][29]]. As exposed above, formation of CO complexes with ASA species growing in parallel for large temperature sets may also induce steric hindrance thus perturbing CO interaction with bridged Si(OH)Al hydroxyl groups.…”

Conversion of ethanol over transition metal oxide catalysts: Effect of tungsta addition on catalytic behaviour of titania and zirconia

“…The conversion of alcohols is also largely used as a test reaction for surface acido-basicity characterization [15][16][17][18]. Dehydration to olefins or ethers is typically observed on acid catalysts but the roles of Brønsted and Lewis acidity on these reactions are still under discussion.…”

Three‐Dimensional Analytical Surface Quantification of Heterogeneous Silica‐Alumina Catalyst Supports

“…The porous volumes remain rather constant after the thermal treatment for both samples as the pore diameters increases slightly, which can be explained by a diminution of the small mesoporosity and probably also of the microporosity inside the grains. This is compatible with the generation of mobile Si species under steaming conditions, and the small mesoporosity originates essentially from silica‐rich zones.…”

“…Among the different methods used systematically, thermal treatment can play a significant role by changing the texture significantly and dispersing the silica or alumina in the support . The difference in behaviour after the steaming of materials produced by the grafting of molecular silica precursors on alumina and the grafting of molecular alumina precursors on silica gives an insight to the kind of mobile species under steaming conditions . Steaming has an effect on the acidic sites on both kinds of samples.…”