Viviana M. Benitez

About the importance of surface W species in WOx/Al2O3 during n-butene skeletal isomerization

Abstract WO x /Al 2 O 3 is accepted as an active catalyst for the skeletal isomerization of n -butene. We have analyzed the effect of preparation conditions on the properties of WO x /Al 2 O 3 . Catalysts were prepared by an equilibrium-adsorption method followed by different drying procedures and they were characterized by TPR, laser Raman spectroscopy, NH 3 -TPD, XRD and catalytic activity and selectivity. The active catalysts present Raman bands and TPR profiles that indicate the presence of tetrahedrally coordinated WO x species. The poorly active catalysts show, in addition, WO x species in octahedral coordination which decrease total acidity and disrupt the contiguous tetrahedral sites necessary for the bimolecular reaction mechanism.

Influence of Support Material on the Activity and Selectivity of Pt–Ir Catalysts for Ring Opening Reactions

The influence of the supports (Al2O3, TiO2 and SiO2) on the activity and selectivity of Pt–Ir catalysts for the ring opening (RO) of decalin was studied. It was found that the properties of the supports strongly influence the distribution, size and Pt–Ir interaction of the metal particles. They therefore also influence the catalytic activity for reactions like dehydrogenation and hydrogenolysis, but also specifically the activity for RO reactions of naphthenes. Via their acid sites the supports influence RO reactions although the effect is not very marked on conversion because the acidity differences are not very significant among them. The results show that the highest decalin conversion for three different supports, alumina, silica and titania, is obtained with the catalysts of highest metal loading. The best selectivity to RO products is obtained with Pt–Ir(1.0)/Al2O3 catalyst. Moreover this catalyst shows the highest performance for MCP RO.Graphical Abstract.

Poisoning and regeneration of Pt-Pd/WO3-ZrO2 short paraffin isomerization catalysts

WO3-ZrO2 catalysts promoted with Pt and Pd were tested as paraffin isomerization catalysts using n-hexane as model compound. Sulfur and amine poisoning and regeneration tests were used to assess the impact of the addition of Pt and Pd on the deactivation resistance and regenerability. Pt and PtPd catalysts were the most active for n-hexane isomerization. The low activity of the Pd catalyst was attributed to poor Pd metal properties when supported over WO3-ZrO2 and to a decrease of the number of BrQnsted acid sites. PtPd was the only catalyst capable of full regeneration after S poisoning. Amine poisoning completely supressed the isomerization activity and the original activity could only be restored by calcination and reduction.

Isomerization-cracking of n-octane on catalysts based on heteropolyacid H3Pw12O40 and heteropolyacid supported on zirconia and promoted with Pt and Cs

Isomerization - cracking of n-octane was studied using H3PW12O40 (HPA) and HPA supported on zirconia and promoted with Pt and Cs. The addition of Pt and Cs to the supported HPA did not modify the Keggin structure. The Pt addition to the supported HPA did not substantially modify the total acidity; however, the Bronsted acidity increased significantly. Cs increased the total acidity and Bronsted acidity. A linear relation was observed between the n-C8 total conversion and Bronsted acidity. The most adequate catalysts for performing isomerization and cracking to yield high research octane number (RON) are those with higher values of Bronsted acidity.

Modification of the performance of WO3-ZrO2 catalysts by metal addition in hydrocarbon reactions

A study of the different hydrocarbon reactions over Ni doped WO3-ZrO2 catalysts was performed. Ni was found as NiO at low Ni concentration while at high Ni concentrations a small fraction was present as a metal. For both cases, Ni strongly modified total acidity and concentration of strong acid sites. In the cyclohexane dehydrogenation reaction, Ni addition promotes both benzene and methyl cyclopentane production. The hydroconversion activity (n-butane and n-octane) increases with the augment of total acidity produced by Ni. The selectivity to reaction products is modified according to the acid strength distribution changes produced by Ni addition.