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

Robert Hubaut (1, 2) , Bouchta Ouled Ben Tayeb (3) , Wenxing Kuang (4) , Alain Rives (2) , Michel Fournier (2)

1 LCL - Laboratoire de catalyse de Lille - UMR 8010
2 UCCS - Unité de Catalyse et Chimie du Solide - UMR 8181
3 ENS Fès - École normale supérieure - Fès
4 Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario, Canada KIN 6N5

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.

Domaines: Catalyse

Robert Hubaut, Bouchta Ouled Ben Tayeb, Wenxing Kuang, Alain Rives, Michel Fournier. Mechanical Mixtures of Me (Ni, Pd) Ce Oxides and Silica-Supported Heteropolyacids: Role and Optimal Concentration of Each Active Species in n-Hexane Isomerization. Kinetics and Catalysis, 2006, 47, pp.20. ⟨10.1134/S0023158406010046⟩. ⟨hal-00023862⟩