Synthesis of Cu/SiO2(MCM-41) mesostructured catalysts: Effect of the preparation method on the textural properties and chemical structure

Abstract

Two Cu/SiO2 mesoporous materials (Cu-MCM-41) were synthesized, one by the ion exchange (IE) post-synthesis method and the other, by the sol-gel (SG) method by co-precipitation of copper and silica (Cu-MCM-41) in the cetyltrimethylammonium bromide (CTAB) presence. The effects of the synthesis method on these materials were analyzed. They were characterized by XRD, N2 adsorption-desorption, TEM, DRUV–vis, FTIR, TPR, XPS, and FTIR with both, CO and pyridine adsorbed. Using the SG method, an MCM-41 material with a uniform mesoporous structure (Dp ≈ 35 Å), and a specific surface area (SBET) of 800 m2.g-1, was obtained. With the IE method and due to the partial collapse of the SiO2-MCM-41 mesoporous structure used as support, a material with a lower SBET (560 m2.g-1) was produced. The Cu in the SG synthesized material was mainly constituted by SiO-[CuO]n-CuOSi polymeric species and small CuO agglomerates. On the other hand, in the IE material, the copper was in the form of isolated SiO–Cu–OSi monomers, SiO–Cu–O–Cu–OSi dimers, and only a low proportion of SiO-[CuO]n-CuOSi oligomers. The catalytic activity of both materials was tested against the 2-propanol (2-PrOH) dehydrogenation in the gas phase. The reaction rate of the IE synthesized material was an order of magnitude higher than that prepared by the SG method. This behavior was attributed to the presence of SiO–Cu+ pair formed by the reduction of SiO–Cu–O–Cu–OSi dimmers present in the material prepared by IE; in contrast with the CuO aggregates obtained by the SG method.