The acidity of a prereduced Cu/SiO 2 catalyst was extensively investigated by means of FT-IR of adsorbed pyridine and by titration with 2phenylethylamine in cyclohexane. Comparison with the parent CuO/SiO 2 material, which was already shown to exhibit Lewis acid sites due to the high dispersion of the CuO phase, provided evidence that reduction of this phase to the metallic state increases the acidity of the material. This allowed us to set up a bifunctional catalyst showing acidic and hydrogenation activity, both ascribable to the presence of the metal particle, without the need of an acidic support. This catalyst was tested in the one-pot transformation of γ−valerolactone into pentyl valerate and showed comparable activity (91% vs 92% conversion) and improved selectivity (92% vs 72%) with respect to the previously reported copper catalyst supported on acidic material. The role of Cu in activating the substrate was also evidenced through FTIR of adsorbed γ-valerolactone.

Keywords dry reforming of methane, silica supported nickel catalyst, nickel-indium bimetallic catalyst, coke formation, biogas conversion Highlights· Ni-In/SiO 2 catalysts were prepared by deposition-precipitation with urea. · Both metals were in metallic state after reduction at 700 °C. · Interaction of the two metals was evidenced by TPR, XPS. · The presence of indium in the close vicinity of nickel prevents coke formation. Graphical abstract AbstractThe development of a carbon tolerant nickel catalyst for carbon dioxide reforming of methane (dry reforming of methane, DRM) has been in the focus of catalysis research for several years.In the present study, 3wt%Ni/SiO 2 and bimetallic 3wt%Ni-2wt%In/SiO 2 catalysts (corresponding to 3:1 Ni:In ratio) were prepared by deposition precipitation with urea. Our intention was to modify the nickel surface with a second metal which is known from its ability to reduce surface coke formation. A methane rich reaction mixture (CH 4 :CO 2 :Ar = 2 69:30:1) was used for the catalytic tests at 600 °C and 675 °C. TPO measurements after the catalytic tests showed that there was no surface carbon formation on the indium containing catalyst.Temperature-programmed reduction measurements of the catalysts showed that both nickel and indium was completely reduced after one hour reduction at 700 °C suggesting interaction of the two metals. CO pulse chemisorption experiments revealed that the particle size was similar on the monometallic and bimetallic catalyst, and CO-TPD measurements showed completely different desorption behavior of CO, suggesting the presence of different active sites on the two catalysts. XPS experiments gave similar results, furthermore it was found that after reduction, the Ni/In ratio on the surface was 2.2 compared to the initial value (~3), which refers to the surface enrichment of indium in the bimetallic particles.The lack of coke formation on the indium containing catalyst might be explained by the interplay between a geometric and a chemical effect, that is, indium atoms are most likely situated on the edge and step sites of a nickel particle, influencing reactant adsorption and hindering the growth of carbon nanostructures and/or providing an oxygen rich indium suboxide surface through the reaction with CO 2 in the close vicinity of catalytically active nickel sites, which also inhibits the accumulation of carbon deposits during DRM.

No abstract

Anion exchange membrane fuel cells (AEMFCs) offer several important advantages with respect to proton exchange membrane fuel cells, including the possibility of avoiding the use of platinum catalysts to help overcome the high cost of fuel cell systems. Despite such potential benefits, the slow kinetics of the hydrogen oxidation reaction (HOR) in alkaline media and limitations in performance stability (because of the degradation of the anion conducting polymer electrolyte components) have generally impeded AEMFC development. Replacing Pt with an active but more sustainable HOR catalyst is a key objective. Herein, we report the synthesis of a Pd−CeO 2 /C catalyst with engineered Pd-to-CeO 2 interfacial contact. The optimized Pd−CeO 2 interfacial contact affords an increased HOR activity leading to >1.4 W cm −2 peak power densities in AEMFC tests. This is the only Pt-free HOR catalyst yet reported that matches state-of-the-art AEMFC power performances (>1 W cm −2 ). Density functional theory calculations suggest that the exceptional HOR activity is attributable to a weakening of the hydrogen binding energy through the interaction of Pd atoms with the oxygen atoms of CeO 2 . This interaction is facilitated by a structure that consists of oxidized Pd atoms coordinated by four CeO 2 oxygen atoms, confirmed by X-ray absorption spectroscopy.

No abstract