Physicochemical properties of WOx/ZrO2 catalysts for palmitic acid esterification

• Preparation of WOx/ZrO2 solid catalysts via incipient-wetness impregnation.
• Catalyst based on W-containing zirconia for heterogeneous esterification reaction.
• Fatty acids catalytic heterogeneous esterification reaction using CH3OH.
• Catalytic activity is associated with the surface W density, calcination temperatures and formation of polymeric tungstate species on zirconia.
• Catalyst with efficiency and recyclability capacity.

A series of WOx/ZrO2 with various tungsten loadings was prepared via incipient-wetness impregnation of zirconium hydroxide. The resulting thermally processed materials were characterised by XRD, XPS, porosimetry, NH3-TPD and pyridine FTIR spectroscopy to elucidate their composition, morphology and acidity, and subsequently tested in the esterification of palmitic acid with methanol. Catalytic performance was strongly dependent upon calcination temperature and W surface density. Esterification activity increased with increasing surface W density, reaching a maximum at 8.9 W nm−2 corresponding to near monolayer coverage. Subsequent growth of crystalline WO3 lowered activity, consistent with a decrease in the density of active surface sites. Calcination temperatures as high as 800 °C increased surface acidity and hence catalytic activity. The formation of polymeric tungstate species on zirconia is necessary to generate the Brönsted acid sites responsible for palmitic acid esterification under mild conditions.

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