Preparation of nanosize Pt clusters using ion exchange of Pt(NH3)(4)(2+) inside mesoporous channel of MCM-41

Abstract

Mesoporous molecular sieve MCM-41 with a Si/Al ratio of 35 was obtained by hydrothermal synthesis using a gel mixture with a molar composition of 6 SiO2 : 0.1 Al2O3 : 1 hexadecyltrimethylammonium chloride : 0.25 dodecyltrimethylammonium bromide : 0.25 tetrapropylammonium bromide : 0.15 (NH4)(2)O : 1.5 Na2O : 300 H2O. The MCM-41 sample was calcined in O-2 flow al 813 K and subsequently ion exchanged with Ca2+. A small Pt cluster has been supported on the MCM-41 sample following a procedure using ion exchange of Pt(NH3)(4)(2+). The Pt(NH3)(4)(2+) ion supported on MCM-41 has been activated in O-2 flow at 593 K and subsequently reduced with H-2 flow at 573 K, in the same way used for the preparation of a Pt cluster entrapped inside the supercage of zeolite NaY. The resulting Pt cluster supported on the MCM-41 shows hydrogen chemisorption of total two H atoms per Pt at 296 K (based on the total amount of Pt) and high catalytic activity for hydrogenolysis of ethane. The chemical shift in Xe-129 NMR spectroscopy of adsorbed xenon indicates that the Pt cluster is located inside the mesoporous molecular sieve.