Chromium promotion of tungstated zirconia catalysts for the isomerization of n-alkanes

Tungstated zirconia (WZ) and WZ promoted by platinum (PtWZ) were tested for their catalytic performance in the isomerization of n-pentane to isopentane. It was shown that the additional promotion by a transition metal oxide, namely iron oxide (PtFeWZ) or chromium oxide (PtCrWZ) led to significant improvements of activity, selectivity and stability of the catalysts. The chromium-promoted material PtCrWZ was shown to be the most promising catalyst giving yields close to the thermodynamic equilibrium value at given reaction temperatures and selectivities to i-C5 close to and greater than 99%. The high activity of the Cr-promoted catalyst permits operation at low reaction temperatures (<200 °C), i.e., under thermodynamically favorable reaction conditions. The oxidation state of the chromium is 3+ or lower, and is therefore environmentally benign.