Hydrogenation on Palladium Nanoparticles Supported by Graphene Nanoplatelets.

Klaus Dobrezberger,Nico Moser,Nevzat Yigit,Günther Rupprechter,Andreas Nagl,Johannes Bosters,Karin Föttinger,David Lennon

doi:10.1021/acs.jpcc.0c06636

Klaus Dobrezberger, Nico Moser + Show 6 more

Open Access

https://doi.org/10.1021/acs.jpcc.0c06636

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Abstract

Pd nanoparticles (1 wt %; mean size ∼4 nm) were supported on ∼2 μm sized, but few nanometers thick, graphene nanoplatelets (GNPs) and compared to 1 wt % Pd on activated carbon or γ-alumina. Catalyst morphology, specific surface area, and Pd particle size were characterized by SEM, BET, and TEM, respectively. H2-TPD indicated that GNPs intercalated hydrogen, which may provide additional H2 supply to the Pd nanoparticles during C2H4 hydrogenation. Whereas the two types of Pd/GNPs (NaOH vs calcinated) catalysts were less active than Pd/C and Pd/Al2O3 below 40 °C, at 55 °C they were about 3–4 times more active. As for example Pd/GNPs (NaOH) and Pd/Al2O3 exhibited not too different mean Pd particle size (3.7 vs 2.5 nm, respectively), the higher activity is attributed to the additional hydrogen supply likely by the metal/support interface, as suggested by the varying C2H4 and H2 orders on the different supports. Operando XANES measurements during C2H4 hydrogenation revealed the presence of Pd hydride. The Pd hydride was more stable for Pd/GNPs (NaOH) than for Pd/C, once more pointing to a better hydrogen supply by graphene nanoplatelets.

Highlights

Supported Pd catalysts are important for industrial hydrogenation reactions, including fine chemicals synthesis.[1−3] Palladium is considered the most selective among the platinum metals, as hydrogenation is much faster than dehydrogenation to undesired carbonaceous species
Graphene nanoplatelets (GNPs) and palladium acetate as metal precursor[45] were used for two types of synthesis: (i) wet impregnation with formaldehyde as reducing agent[46] in basic medium (NaOH; pH 12)[47] and (ii) wet impregnation followed by calcination in air
The graphene nanoplatelets (GNPs) were typically less than 2 μm in diameter and a few nanaometers in thickness but often seem thicker due to stacking/aggregation

Summary

INTRODUCTION

Supported Pd catalysts are important for industrial hydrogenation reactions, including fine chemicals synthesis.[1−3] Palladium is considered the most selective among the platinum metals, as hydrogenation is much faster than dehydrogenation to undesired carbonaceous species. The nature of the support has a strong influence on performance, with carbon-based materials, alumina, and silica being most frequently applied Resulting from their practical importance, technological as well as model catalysts of Pd/ Al2O3, Pd/Fe3O4, or Pd/C (activated carbon, nanotubes, planar graphene layers, highly oriented pyrolytic graphite (HOPG), etc.) have been repeatedly studied for the (selective) hydrogenation of for example ethylene,4−9 1,3-butadiene,10−13 1-butene,[14] acetylene,5,15 1-propyne,[16,17] unsaturated aldehydes,[18] and others.[4,19−21] For reviews and more detailed accounts we refer to refs 21−33. More detailed (preferentially operando) studies are required, but the current results already indicate the high potential of Pd supported on graphene nanoplatelets as a hydrogenation catalyst

METHODS

RESULTS AND DISCUSSION

Pd Nanoparticles Supported by Graphene

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES