A study of the active sites of the mesoporous molecular sieve MCM-41 and related zeolitic materials by using Fourier-transform IR, continuous-wave ESR and pulsed ESR spectroscopic probes

Infrared spectroscopic measurements have been made on hydrocarbons and hydrogen cyanide adsorbed, separately and competitively, on mesoporous molecular sieves MCM-41 of all-silica composition and with various aluminium(III), titanium(IV) or vanadium(V) contents. Similar i.r. spectroscopic measurements were made on the porous aluminium phosphates AlPO4-5 and VPI. Characterization of the cationic binding sites of MCM-41 has been achieved by comparison of the e.s.r. spectra of the cationic copper(II) chelate acetylacetonatocopper(II) tetramethylethylenediamine, adsorbed by MCM-41, and by the sodium ion forms of zeoiite-Y, mordenite, ultrastable and chromatographic grade silica. Both sets of results show that for mesoporous MCM-41 Bronsted acidity and possibly cation-exchange sites arise from ill-defined structural defects and from the silanol groups which are not greatly influenced by the presence of metal cations within the thick-walled honeycomb structure.