(45i) Energy Efficient Catalysis Using Nanoparticle-Deposited Supported Metal Oxides

As demands for cleaner and cheaper energy rise, improvements to current fuel technologies are systematically studied. Among the very important fuel enrichment processes in the petrochemical industry, paraffin isomerization using Pt-doped Al2O3 catalysts is of great significance. Nevertheless, this catalytic system has the disadvantage of chlorinated compound generation that leach out and require further purification. A system that uses tungstated zirconia (WOx/ZrO2) catalyst offers a promising alternative as a less energy-intensive and more environmentally friendly process. However, its stable but relatively low activity due to surface heterogeneity issues prevents this from happening. Recent studies demonstrated that the enhanced pentane isomerization catalytic activity of WOx/ZrO2 was associated with the existence of WOx nanoclusters (~1 nm). These nanospecies have an ideal cluster density that allows them to successfully delocalize protons to form the appropriate Brønsted sites. Based on that observation, the synthesis of a WOx/ZrO2 catalyst with high concentrations of these WOx nanoclusters would resolve this low activity issue. In this study, we report a highly efficient non-aqueous solvothermal technique for ex situ synthesis of WOx nanoparticles (NPs) followed by a deposition step. In a single step, WOx raft-shaped NPs (1-2 nm) were consistently produced and characterized using high resolution transmission electron microscopy, atomic force microscopy, and x-ray diffraction. WOx/ZrO2 catalysts were prepared by dry impregnation of a toluene suspension of WOx NPs onto ZrO2 support. Drying and calcination at 70 °C and 500 °C respectively led to complete removal of the oleylamine. Preliminary data showed that this material was less active than conventional WOx/ZrO2, possibly due to particle sintering upon calcination. Ligand exchange to remove part of the oleylamine, prior to calcination at 40 °C, increased the n-pentane isomerization activity by 50%, indicating the importance of chemical removal of the ligands. Further improvements in ligand removal techniques should lead to improved catalytic materials.