Aerosol-Assisted Sol-Gel Synthesis of Mesoporous TiO2 Materials, and Their Use as Support for Ru-Based Methanation Catalysts

Mesoporous TiO₂ materials have been prepared by an aerosol process, which leverages on the acetic acid-mediated sol-gel chemistry and on the evaporation-induced self-assembly phenomenon to obtain materials with high specific surface area and large mesoporous volume. The obtained spherical particles are calcined to release the porosity. It is shown that the mesoscopic order can be preserved when the calcination is carried out at relatively low temperature (375 °C and below). Harsher calcination conditions lead to the progressive destruction of the mesostructured, concomitant with a progressive drop of textural properties and with the crystallization of larger anatase domains. The mesoporous TiO₂ material calcined at 350°C (specific surface area = 260 m².g^-1; pore volume = 0.36 cm³.^-1; mean pore diameter = 5.4 nm) was selected as a promising support for preformed RuO₂ nanoparticles, and subsequently annealed in air. It is shown that the presence of RuO₂ nanoparticles and subsequent annealing provoke further intense modification of the texture and crystallinity of the TiO₂ materials. In addition to a drop in the textural parameters, a RuO₂-mediated crystallization of rutile TiO₂ is highlighted at temperature as low as 250°C. After an in situ reduction in H₂, the catalysts containing TiO₂ rutile and relatively small RuO₂ crystals showed the highest activity in the methanation of CO₂.