Fig. 4: Proposed models for BAS on ASA generated by. | Nature Communications

Fig. 4: Proposed models for BAS on ASA generated by.

From: Acidity enhancement through synergy of penta- and tetra-coordinated aluminum species in amorphous silica networks

Fig. 4

a one Al center per SiOH for moderate BAS, and b two Al centers per SiOH group, leading to moderate or zeolitic acidity strengths. The acid strength is estimated by measuring the 13C isotropic chemical shift of CH313COCH3, which is loaded on dehydrated samples on a vacuum line, followed by evacuation at room temperature for 1 h to remove weakly adsorbed molecules.

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