The variety of Brønsted acid sites in amorphous aluminosilicates and zeolites

Abstract

Brønsted acid sites of similar strength to those in zeolites are found in ASAs prepared by cogelation, as shown by thermogravimetric study of the dehydration of ethanol to ethylene. ASAs prepared by grafting and a commercial ASA (Siralox 30) show Brønsted acid sites that differ from those of zeolites. CO respectively ethanol adsorption followed by infrared spectroscopy identified the OH stretching frequency of the Brønsted acid sites specific to Si/Al 2 O 3 and Al/SiO 2 materials obtained by grafting to be ca. 3600 cm-1 and 3640 cm-1 , respectively, although the intensity of the corresponding band is weak. These sites, contrary to those of a H-USY zeolite with very few extraframework aluminium, are highly sensitive to the surface hydration state: Their number decreases with increasing temperature. The surface structure of Siralox 30 resembles that of Si/Al 2 O 3 prepared in anhydrous conditions, showing similar isosurface acidic properties and distribution of silicon species.

Tuning of acidity in CeY catalytic cracking catalysts by controlling the migration of Ce in the ion exchange step through valence changes

“…the yields for gasoline and light cycle oil (LCO) were increased by 0.5 and 1.03 wt%, respectively, compared with the amounts from CAT-CeUSY N2 . The higher gasoline and LCO selectivity of CAT-CeUSY O2 is attributed to the higher amount of strong Brønsted acid sites and higher value of B/L ratio; this is in accordance with the literature results indicating that for all cracking reactions, the cracking activity is clearly related to strong protonic acidity [50][51][52]. CAT-CeUSY O2 was found to provide sufficient active centers (B type acid), and CAT-CeUSY N2 demonstrated limited deep cracking due to the Lewis acid centers.…”

Pyrolysis of the Cellulose Fraction of Biomass in the Presence of Solid Acid Catalysts: An Operando Spectroscopy and Theoretical Investigation

“…DFT simulations of CO andH 2 Oa dsorptiono nacoordinatively unsaturated Al 3 cluster andcorrespondinge xperimental in situ IR spectra of CO adsorption. signed to silanol groups interacting with CO. [80] The hydroxyl n OH bands at 3566-3600 and around3 470 and 3320 cm À1 are assigned to CO interacting with three Brønsted acid sites (BAS) of different strength,r eferred to herein as weak, medium, and strong BAS, respectively. The Al site acts as aweak Lewis centre (n CO = 2204cm À1 )and the neighboringb ridgingO Hg roup is aw eak Brønsted centre( m-OH 3573cm À1 + CO = 3540 cm À1 ;T able S5).…”

Metal Oxide Nanoparticles Supported on Macro-Mesoporous Aluminosilicates for Catalytic Steam Gasification of Heavy Oil Fractions for On-Site Upgrading

“…TPD-NH 3 profiles of ammonia desorption for clay, metakaolin, and their functionalization are shown in Figure 1 and results of total acidity are listed in Table 2. From Figure 1 two predominant peaks at 590 K and 845 K for fresh clay can be observed due to the presence of Lewis and Brønsted sites [79,81]. The low-temperature peak observed in a TPD profile is related to the Lewis sites.…”