Deactivation and coke formation on palladium and platinum catalysts in vegetable oil hydrogenation

Abstract

Deactivation of palladium and platinum catalysts due to coke formation was studied during hydrogenation of methyl esters of sunflower oil. The supported metal catalysts were prepared by impregnating γ-alumina with either palladium or platinum salts, and by impregnating α-alumina with palladium salt. The catalysts were reused for several batch experiments. The Pd/γ-Al 2 O 3 catalyst lost more than 50% of its initial activity after four batch experiments, while the other catalysts did not deactivate. Samples of used catalysts were cleaned from remaining oil by repeated extractions with methanol, and the amount of coke formed on the catalysts was studied by temperature-programmed oxidation. The deactivation of the catalyst is a function of both the metal and the support. The amount of coke increased on the Pd/γ-Al 2 O 3 catalyst with repeated use, but the amount of coke remained approximately constant for the Pt/γ-Al 2 O 3 catalyst. Virtually no coke was detected on the Pd/α-Al 2 O 3 catalyst. The formation of coke on Pd/α-Al 2 O 3 may be slower than on the Pd/γ-Al 2 O 3 owing to the carrier's smaller surface area and less acidic character. The absence of deactivation for the Pt/γ-Al 2 O 3 catalyst may be explained by slower formation of coke precursors on platinum compared to palladium. , temperature-programmed oxidation (TPO). FIG. 2. (A) Measured coke content on samples contacted with oil for various times and temperatures. (B) Coke formation on the catalysts vs. time on-stream. Each symbol indicates one batch. The coke concentration was not analyzed for the Pd-α-Al 2 O 3 catalyst after batches 2 and 3. The other two curves represent catalysts on γ-Al 2 O 3 support.

Palladium catalyst on anodized aluminum monoliths for the partial hydrogenation of vegetable oil

“…This may also include reactants strongly adsorbed on the metal or on the support, as well as the more dehydrogenated species present on the catalyst. This result is in agreement with those reported by Edvardsson et al [33]. They investigated the Pd and Pt catalyst deactivation supported on ␣-and ␥-Al 2 O 3 by coke formation during hydrogenation of vegetable oil in liquid phase.…”

Hydrodeoxygenation of microalgae oil to green diesel over Pt, Rh and presulfided NiMo catalysts

“…The definition of what constitutes coke in liquid-phase reactions, especially for liquids with high boiling point, depends on the coke quantification method, and is quite different from that in gas-phase reactions [34]. Moreover, coke formation during the catalytic upgrading of carbon-rich feedstock is one of the major causes of catalyst deactivation.…”

Hydrogenation of Sunflower Oil over M/SiO2 and M/Al2O3 (M = Ni, Pd, Pt, Co, Cu) Catalysts

“…Although the cost is an important drawback, their much higher activity and the possibility to be reused make noble metal catalysts a promising alternative. In this regard, palladium catalysts are more selective to cis isomers than nickel catalysts during the hydrogenation of polyunsaturated fatty acids [4]. Platinum has been found to be highly active and, in general, forms less trans isomers than nickel during hydrogenation [5].…”

“…Platinum has been found to be highly active and, in general, forms less trans isomers than nickel during hydrogenation [5]. Between both metals, it has been reported in the literature that the formation of trans isomers is lower for platinum catalysts, compared to palladium catalysts [4].…”