MCM-41 is proposed to build mesostructured γ-Fe₂O₃-based sorbents as an alternative to other silica or alumina supports for mid-temperature H₂S removal.

SBA-15 functionalization with mercaptopropyltrimethoxysilane has been used to prepare supported gold catalysts for the low temperature CO oxidation reaction. Supports and catalysts have been characterized by chemical analysis, CHS analysis, XRD, TGA, nitrogen adsorption–desorption at 77 K, TEM, CPMAS NMR, XPS and EPR. Catalytic runs have been carried out at atmospheric pressure and 313–623 K and the influence of diverse thermal treatments of the samples prior to reaction has been investigated. The presence of organic residues and the size of the gold nanoparticles strongly affect catalytic activity. Only high-temperature calcination in air followed by treatment under H₂ atmosphere leads to active catalysts. After complete elimination of the functionalizing agent, caused by the calcination step, a gold-mediated “activation” process of the silica support takes place during the hydrogen treatment. As a consequence, active catalysts for the low temperature CO oxidation are obtained, even though the size of the Au particles is too large for establishing direct Au–oxygen interactions, usually assumed to be essential for the reaction over silica-supported gold catalysts.

Supported nickel catalysts were synthesized, characterized, and employed in the carbon oxides co-methanation process. Five NiO/CeO₂-ZrO₂ mixed oxides, with the same Ni content and different Ce/Zr molar ratios, were prepared by the soft-template method. They were characterized through ICP-AES, N₂ adsorption, XRD, and TPR. Reduced Ni/CeO₂-ZrO₂ catalysts were obtained by submitting the oxide systems to reduction treatment in H₂ at 400 °C. They were characterized by XRD, H₂-TPD, and CO₂ adsorption microcalorimetry and their catalytic performances in the carbon oxides co-methanation were investigated. Catalytic tests were performed in a fixed-bed continuous-flow microreactor at atmospheric pressure. The effect of experimental conditions (reaction temperature, space velocity, reactants molar ratio) was also studied. Almost complete CO conversion was obtained on any catalyst, whereas CO₂ conversion was much lower and increased with Ce content, at least up to Ce/Zr = 1. The beneficial effect of the Ce content could be related to the increased NiO reducibility and to the higher ability to adsorb and activate CO₂. However, at high Ce/Zr ratios, it is probably counterbalanced by an interplay of reactions involving CO and CO₂.

Nanosized NiO, CeO₂ and NiO-CeO₂ mixed oxides with different Ni/Ce molar ratios were prepared by the soft template method. All the samples were characterized by different techniques as to their chemical composition, structure, morphology and texture. On the catalysts submitted to the same reduction pretreatment adopted for the activity tests the surface basic properties and specific metal surface area were also determined. NiO and CeO₂ nanocrystals of about 4 nm in size were obtained, regardless of the Ni/Ce molar ratio. The Raman and X-ray photoelectron spectroscopy results proved the formation of defective sites at the NiO-CeO₂ interface, where Ni species are in strong interaction with the support. The microcalorimetric and Fourier transform infrared analyses of the reduced samples highlighted that, unlike metallic nickel, CeO₂ is able to effectively adsorb CO₂, forming carbonates and hydrogen carbonates. After reduction in H₂ at 400 °C for 1 h, the catalytic performance was studied in the CO and CO₂ co-methanation reaction. Catalytic tests were performed at atmospheric pressure and 300 °C, using CO/CO₂/H₂ molar compositions of 1/1/7 or 1/1/5, and space velocities equal to 72000 or 450000 cm³·h⁻¹·g_cat⁻¹. Whereas CO was almost completely hydrogenated in any investigated experimental conditions, CO₂ conversion was strongly affected by both the CO/CO₂/H₂ ratio and the space velocity. The faster and definitely preferred CO hydrogenation was explained in the light of the different mechanisms of CO and CO₂ methanation. On a selected sample, the influence of the reaction temperature and of a higher number of space velocity values, as well as the stability, were also studied. Provided that the Ni content is optimized, the NiCe system investigated was very promising, being highly active for the CO_x co-methanation reaction in a wide range of operating conditions and stable (up to 50 h) also when submitted to thermal stress.

CO₂-derived methanol and dimethyl ether can play a very important role as fuels, energy carriers, and bulk chemicals. Methanol production from CO₂ and renewable hydrogen is considered to be one of the most promising pathways to alleviate global warming. In turn, methanol could be subsequently dehydrated into DME; alternatively, one-step CO₂ conversion to DME can be obtained by hydrogenation on bifunctional catalysts. In this light, four oxide catalysts with the same Cu and Zn content (Cu/Zn molar ratio = 2) were synthesized by calcining the corresponding CuZnAl LDH systems modified with Zr and/or Ce. The fresh ex-LDH catalysts were characterized in terms of composition, texture, structure, surface acidity and basicity, and reducibility. Structural and acid–base properties were also studied on H₂-treated samples, on which specific metal surface area and dispersion of metallic Cu were determined as well. After in situ H₂ treatment, the ex-LDH systems were tested as catalysts for the hydrogenation of CO₂ to methanol at 250 °C and 3.0 MPa. In the same experimental conditions, CO₂ conversion into dimethyl ether was studied on bifunctional catalysts obtained by physically mixing the ex-LDH hydrogenation catalysts with acid ferrierite or ZSM-5 zeolites. For both processes, the effect of the Al/Zr/Ce ratio on the products distribution was investigated.