Conduction electron paramagnetic resonance of metal nanoparticles in AlMCM-41 aluminosilica mesoporous molecular sieves

Mesoporous aluminosilica molecular sieves AlMCM-41 are loaded with differen t amounts of Ag+, Pd2+ and Pt2+ ions by varying the Si/Al ratio, which chan ges the ion exchange capacity. These metal ions are reduced to metal partic les by hydrogen and characterized by conduction electron paramagnetic reson ance (CEPR). Metal particle sizes were calculated from the Kawabata theory that relates CEPR linewidths to metal particle size. The CEPR linewidths ar e independent of metal ion loading, which suggests that the metal particles are located inside the AlMCM-41 channels and size constrained by the chann el diameter. The calculated metal particle diameters are about 1 nm, which is smaller than the 3.5 nm channel diameter of AlMCM-41. The validity of Ka wabata's theory to such systems may need reexamination.