A comparative study of n-pentane and n-butane isomerization over zirconia-supported tungsten oxide: Pulse and flow studies and DRIFTS catalyst characterization

The reactions of n-pentane and n-butane over both tungstated zirconia (WZ) and platinum supported on tungstated zirconia (PtWZ) in the presence of hydrogen were studied in the pulse mode. Influence of contact time at 666 kPa, and n-pentane flow mode results in an atmospheric pressure packed-bed reactor are reported. The diffuse reflectance infrared (DRIFTS) spectra of adsorbed CO on PtWZ and the tungsten oxide-free sample are compared. The WZ sample was found to be unable to retain CO at room temperature. The behavior of W-O vibrations before and after reduction is also discussed. Acid cracking and isomerization pathways appear to occur on different active sites, in light of pulse experiments. The presence of Pt produces an increase in the number of isomerization sites, but has no obvious positive influence on catalyst deactivation. In addition, it does not promote cracking, but metal-catalyzed hydrogenolysis (internal C-C bond rupture) instead. The isomerization of n-pentane may follow a unimolecular pathway, as seen by the absence of C₆ disproportionation species in the flow mode experiments.