Understanding the effects of synthetic parameters in the catalytic activity of heterogeneous catalysts is of utmost importance when aiming for optimal reaction conditions. Hence, we disclose in this work the synthesis and characterization of cerium-modified MCM-41 materials. In addition, it was observed for the first time, differences in catalytic activity when using different cerium synthetic precursors: CeCl3·7H2O and Ce(NO3)3·6H2O (Ce-MCM-Cl and Ce-MCM-NO3, respectively). A mechanism for cerium incorporation in MCM-41 was proposed, where [Ce(OH)3] species were hydrogen bonded to silicate anions, forming framework Ce-O-Si bonds during condensation and, consequently, causing distortion of the typical hexagonal mesophase. It was also observed that Ce(OH)3 formed aggregated layers with template assemblies during synthesis, resulting in non-framework CeO2 species on the MCM-41 surface after calcination. These CeO2 species were preferentially formed for Ce-MCM-NO3 and were attributed to the nitrate ions’ strong binding to template molecules. In the solvent free liquid-phase oxidation of benzyl alcohol (BzOH), Ce-MCM-Cl achieved better BzOH conversions and benzaldehyde (BzD) yields, while Ce-MCM-NO3 offered increased BzD selectivity. The catalysts’ reusability was also studied over three catalytic runs, where Ce-MCM-NO3 was more resistant than Ce-MCM-Cl towards deactivation. The observed catalytic behavior shows the importance of metal precursors in the obtainment of materials with desirable final properties.
SnO2 microspheres were prepared by an ion exchange technique using a cationic resin as template. The material obtained by calcination was investigated by several techniques and showed singular properties. Removal of the polymeric matrix led to hierarchical layers of hollow SnO2 microspheres with mean particle size of 43 μm and surface area of 27.8 m2 g−1. The Matryoshka‐like structure showed 3 to 5 stacked shells that were comprised by aggregated nanocrystals of 19.6 nm as building blocks. The crystallization into more shells was a unique feature of SnO2 and was attributed to the chemical nature of this oxide. The rutile tetragonal phase obtained showed the presence of crystal defects attributed to the macrotemplating method employed. The SnO2 multi‐shelled morphology reported in this work was obtained by a facile template method followed by calcination, which might be essential in the development of new synthetic routes for the manufacture of micro‐structured materials.
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