Proton Transfer Mediated by Water: Experimental Evidence by Neutron Diffraction

Neutron Rietveld refinement of a synthetic low silica ferrierite (Si/A1 = 8.5) in deuterium form rehydrated with D(2)O vapor (RD-FER) was performed in the Immm space group. Three Bronsted acid sites were identified. The first (D1) was on 04 framework oxygen, occupied to 18%; the second (D2) was on 06, occupied to 8%; the latter (D3) was on O1, occupied to 35%. This Bronsted site distribution strongly differs from that found in the nonrehydrated deuterium form (D-FER) in the same ferrierite sample (Martucci, A.; Alberti, A.; Cruciani, G.; Radaelli, P.; Ciambelli, P.; Rapacciuolo, M. Microporous Mesoporous Mater. 1999, 30, 95.), where D3 site is absent and D1 and D2 are occupied to 14 and 16%, respectively. The discrepancy between the Bronsted sites found in RD-FER and D-FER indicated remarkable acidic proton mobility and was explained by a proton transfer mechanism where water molecules or water clusters act as carriers of protons.