In this work, industrial waste hexafluorosilicic acid (H 2 SiF 6 or FSA) has been proven to be a low-cost alternative to silicate esters for the synthesis of high-quality MCM-41 (high surface area, high degree of order, narrow pore size distribution, high thermal stability) through a head-to-head comparison between the most common silica precursor, tetraethylorthosilicate (TEOS), and FSA. The effect of different parameters such as temperature, time, hydrothermal treatment, and the presence of ethyl acetate has been explored by studying the textural, structural, and morphological features. On the most promising samples, thermal and hydrothermal stability has been assessed, indicating a higher thermal stability for the FSA-derived sample, due to the thicker walls, and comparable hydrothermal stability. The mother solution treatment has allowed the obtainment of nanostructured fluorite as an additional valuable product and a CTAB-rich ammonia solution for successive synthesis with FSA. Recovery processes for the templating agent entrapped in the MCM-41 mesostructure have also been explored for both FSA-and TEOS-derived samples, showing an easier removal in the case of FSA-MCM-41. Moreover, mesostructured silica derived from FSA has also been proven to be an ideal support to design efficient and regenerable mesostructured iron oxide-based sorbents for H 2 S removal from syngas, showing similar performance to that of the corresponding nanocomposite prepared from TEOS.

Cerium dioxide is a scientifically and technologically important material with a wide range of potential applications, particularly in solid oxide fuel cells and catalysis. Herein, we report a study focusing on the synthesis of nanocrystalline cerium dioxide via thermal decomposition of the oxalate salt. Simply by changing reaction conditions (temperature, concentration, acidity, strike) during the precipitation of the cerium solution with oxalic acid, we were able to obtain different morphologies. The main reaction parameters were mapped and linked to the morphology of the final products. Additionally, it was proved that oxalate precipitation is a robust reaction proceeding at relatively extreme contitions. Moreover, the conversion of cerium oxalate to nanocrystalline oxide was followed to monitor the progress of the reaction, the texture evolution, and the grain growth. The results showed that, for unvaried heating cycle, the grain size of converted material is linked to morphology. The thinner was the original microcrystal the smaller were the CeO2 nanocrystals after calcination. In addition, the grains were found smaller near the edges of the ex-oxalate microcrystals. In both cases, this behavior results from asymmetrical limitations of diffusion during grain growth.

In this work, highly dispersed maghemite (-Fe 2 O 3 in form of ultrasmall nanoparticles (about 2 nm) was embedded into a mesostructured silica MCM-41 (about 600 nm) featuring regular submicrometric hexagonal shaped particles via the two-solvent incipient wetness impregnation strategy. The obtained nanocomposite was then tested as H 2 S sorbent in the mid-temperature range. When compared with a commercial sorbent (Katalko JM 32-5), it showed superior performances after the first sulfidation which remained steady over three repeated sulfidation cycles, highlighting the regenerability properties of the composite. In order to evaluate the effect of the length of the pore channels on the accessibility of H 2 S to the active phase, an analogous micrometric-Fe 2 O 3 @MCM-41, featuring micrometric channels and particles of irregular shape was used as reference.

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