Mechanical Mixtures of Me (Ni, Pd) Ce Oxides and Silica-Supported Heteropolyacids: Role and Optimal Concentration of Each Active Species in n-Hexane Isomerization

Catalytic properties of silica-supported heteropolyacids (HPA) in a mechanical mixture with reduced Me–Ce oxides (Me = Ni, Pd) in n-hexane isomerization are studied. The role of each component of the mixed oxides (Ce and, typically, Ni and Pd) and their optimum content has been illuminated: cerium is not only beneficial for eliminating or preventing coke deposition but is also effective for maintaining the Keggin structure of the highly-organized HPA during the reaction and probably allows a better dispersion of the second metal species. Nickel and palladium, present as Ni0 and Pd0, reinforce the activation of the alkane, which is difficult to obtain by means of a direct attack by an acid, and, thus, enhance noticeably the activity of the catalyst. The best mechanical mixtures are obtained with 30–70 wt % NiCeO–HPW/SiO2 and 50–50 wt %Pd0.1CeO–PW/SiO2. These mixtures have the highest efficiency for a Ni/(Ni + W) atomic ratio of 0.66 and a Pd/(Pd + W) ratio of 0.40, respectively. Finally, the conversion of n-hexane is in the order HPW > HSiW >HBW, which seems to be consistent with the order of their acid strength as per the literature, but the isomerization selectivity appears to be slightly higher on HSiW

Mechanical mixtures of PdCeO and HPA/SiO2: structure and reactivity for n-hexane isomerisation

International audienc

Isomerization of n-Hexane over Silica-Supported Heteropoly Acids Promoted by the Reduced Ce–Ni Oxides

International audienc