Experimental study of the deactivation of Pd on anodized aluminum monoliths during the partial hydrogenation of vegetable oil

• Deactivation of Pd/Al2O3/Al catalyst in the partial hydrogenation of sunflower oil.
• Catalysts were widely characterized in order to understand the deactivation behavior.
• Loss in activity was proportional to decreasing percentage metal exposed.
• Fouling with reaction residues over Pd surface.

Partial hydrogenation of sunflower oil was studied over Pd/Al2O3/Al catalysts in a monolithic stirred reactor. The catalyst showed similar or even better activity and selectivity than conventional Pd/Al2O3 catalysts. However, in consecutive runs, a continuous decreasing activity was observed. In order to understand the deactivation phenomena, fresh and spent catalysts were characterized using temperature programmed reduction, N2 adsorption isotherms, dynamic H2 chemisorption, transmission electron microscopy (TEM), atomic absorption spectroscopy, inductively coupled plasma spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, ultrasound adherence tests, and X-ray photoelectron spectroscopy. Furthermore, an extensive number of catalytic tests under different operating conditions were carried out. The loss in activity was proportional to the reduction in metal dispersion. The decrease in Pd dispersion was due to the coverage of the Pd surface. The deactivation occurred due to fouling with reaction residues most probably coming from polymerization and/or cross-linking reactions. The catalysts can be regenerated ex situ using a careful desorption–washing–calcination process, although this requires further research because the temperatures required are too high for Al.

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