Influence of Tin Loading and Pore Size of Sn/MCM-41 Catalysts on the Synthesis of Nopol

Abstract

In this work, we investigate the influence of the Sn-loading and the pore size of MCM-41 materials on catalytic nopol production. Sn(IV) was anchored onto MCM-41 by incipient wetness impregnation with metal coverages within 0.01 and 0.5 Sn nm–2 (i.e., below the monolayer content). We provide evidence that at coverages below 0.06 Sn nm–2, Sn(IV) is predominantly present as isolated centers, whereas at higher coverages octahedral and/or oligomeric species are formed, which exhibit lower catalytic activity. The rate of nopol production over Sn/MCM-41 was ten times higher than that of analogous Sn silica gel materials. The turnover frequency features a maximum as a function of Sn coverage between 0.03 and 0.05 Sn nm–2 for Sn/MCM-41 catalysts and 0.15 Sn nm–2 for Sn silica gel materials. These results show that both the metal content and pore size can be tuned to enhance catalytic performance of Sn/MCM-41 materials.