The catalytic performances of TiO₂-supported Ni catalysts for the methanation of CO₂ have been investigated using different crystalline phases of TiO₂ (rutile and anatase). The catalytic activity of Ni depends appreciably on the nature of the support. The rate for CO₂ hydrogenation decreases in the order of 10Ni/TiO_2-rutile ≫ 10Ni/TiO_2-anatase. The use of a mixture of catalysts containing 70% 10Ni/TiO_2-anatase + 30% 10Ni/TiO_2-rutile allows for a significant increase of the reaction rate related to 100% 10Ni/TiO_2-rutile. Importantly, it has been demonstrated that the two catalysts do not need to be in direct contact for the synergetic effect to occur. DRIFTS operando analysis during the methanation reaction shows that adsorbed CO accumulates on Ni/TiO_2-anatase and not on Ni/TiO_2-rutile, and that the role of the Ni/TiO_2-rutile is to assist the hydrogenation of this adsorbed CO on the Ni/TiO_2-anatase. Increased CO₂ methanation is also observed by adding Ni-free TiO_2-anatase to 10Ni/TiO_2-rutile, indicating that CO_x hydrogenation can also occur on bare TiO_2-anatase if activated hydrogen can be supplied by another source. H₂-TPD analyses and catalytic tests performed after dilution of the catalysts have shown that hydrogen spillover (mediated by surface or gas-phase species) is at the origin of the synergy observed between the two catalysts for the Sabatier reaction.

Glycerol is produced in large quantities as a byproduct of biodiesel, and among others hydroxyacetone (acetol) is an important commodity obtained from glycerol. Metallic Cu has been identified as active site for the dehydration of glycerol to hydroxyacetone and acid and metal sites are known to influence the catalytic performance. In this study, dehydration of glycerol over 5 wt.% copper supported on γ-Al₂O₃, ZrO₂ and SiO₂ was investigated. Catalysts were characterized by N₂ physisorption, H₂-TPR, NH₃-TPD, N₂O chemisorption, XPS, XRD, FTIR of pyridine adsorption. Cu/ZrO₂ exhibited the highest hydroxyacetone yield at 20 % of glycerol conversion and the highest apparent reaction rate. The superior activity of Cu/ZrO₂ was attributed to the highly acidic, both Lewis and Brönsted acidic, nature of the support and positive roles of the interfacial sites. The Weisz-Prater (WP) criterion was applied to confirm the absence of intraparticle diffusion limitations. It was assumed spherical particles and first order reaction. The WP value obtained in the worst scenario was less than 0.3 ensuring no diffusion limitation. Complementary DFT study indicates that both glycerol and hydroxyacetone interact significantly stronger on Cu/γ-Al₂O₃ and Cu/ZrO₂ compared to metallic Cu, suggesting that the active sites are at the interface of Cu particles and the acidic support.