A Study of the Active Sites of the Mesoporous Molecular Sieve MCM-41 and Related Zeolitic Materials by Using Fourier-Transform I.R., Continuous-Wave E.S.R. and Pulsed E.S.R. Spectroscopic Probes

Abstract

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 zeolite-Y, mordenite, ultrastable and chromatographic grade silica. Both sets of results show that for mesoporous MCM-41 Brønsted 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.