Selective Partial Hydrogenation of Acrolein on Pd: A Mechanistic Study

Abstract

Identifying the surface processes governing the selectivity in hydrogenation of α,β-unsaturated carbonyl compounds on late transition metals is crucial for the rational design of new catalytic materials with the desired selectivity towards C=C or C=O bond hydrogenation. The partial selective hydrogenation of acrolein on a Pd(111) single crystal and Fe3O4-supported Pd nanoparticles under well-defined UHV conditions was investigated in the present study as a prototypical reaction. Molecular beam techniques were combined with infrared reflectionabsorption spectroscopy (IRAS) and quadrupole mass spectrometry (QMS) in order to simultaneously monitor the evolution of surface species and the formation of the final gas-phase products under the isothermal reaction conditions as a function of surface temperature. Over a Pd(111) single crystal, acrolein is hydrogenated at the C=O bond to form the desired reaction product propenol with nearly 100% selectivity in the temperature range between 250 and 300 K, while over Pd/Fe3O4, selective hydrogenation of the C=C bond to form propanal occurs. We found that the exceptionally high selectivity towards C=O bond hydrogenation over Pd (111) This process prevents formation of well-ordered overlayers of oxopropyl species required for selective C=O bond hydrogenation resulting in only minor non-selective hydrogenation of acrolein. At temperatures below 250 K on Pd(111), only a small fraction of the initially adsorbed acrolein is converted into the oxopropyl species yielding a partially modified surface and thus rather unselective formation of both products propanal and propenol.

Structure Sensitivity of Acrolein Hydrogenation by Platinum Nanoparticles on BaxSr1−xTiO3Nanocuboids

“…[54] Af urther striking example is the hydrogenation of AC on Pd(111)/Fe 3 O 4 and Pd N / Fe 3 O 4 catalysts. [55,56] As pectator oxopropyl layer on Pd(111) contributed to an over 99 %s electivity for AA, whereas Pd N becamec overed with CO and only hydrogenated at C=Ct o produce primarily PA.T he native Pd(111)s urface is known to produce 1-propanol (PP) primarily,s ot he "spectator" is av ital component to activate the C=Ob ond and suppress C=Ch ydrogenation. These resultsr einforce the concept that topologically complex sites andt heir manipulation are key to favor/ select catalytic products,e ven thoughi ti sn ot always clear what stages of the reaction pathway are affected.…”

“…Conversely, thiophene adsorption on Cu/Al 2 O 3 catalysts augments C=O hydrogenation greatly . A further striking example is the hydrogenation of AC on Pd(1 1 1)/Fe 3 O 4 and Pd N /Fe 3 O 4 catalysts . A spectator oxopropyl layer on Pd(1 1 1) contributed to an over 99 % selectivity for AA, whereas Pd N became covered with CO and only hydrogenated at C=C to produce primarily PA.…”

Partial Hydrogenation of Unsaturated Carbonyl Compounds: Toward Ligand-Directed Heterogeneous Catalysis

“…This correlated appearance and development of the surface adsorbates related to the vibration at 1120 cm -1 and the formation rates of molecular propenol monitored in the gas phase strongly suggest that the related surface species must be a direct reaction intermediate (RI). Several other bands, appearing at 1090 cm -1 , 1463-1450 cm -1 , 2966 cm -1 and 2980 cm -1 , follow an identical time evolution pattern [12][13][14] and therefore can be also associated with RI. The vibrations at 2966 cm -1 and 2980 cm -1 are characteristic to C-H stretching modes with the band at 2980 cm -1 being typically assigned to a C-H fragment, in which the carbon atom is involved into the C=C bond.…”

Molecular beam/infrared reflection-absorption spectroscopy apparatus for probing heterogeneously catalyzed reactions on functionalized and nanostructured model surfaces

“…Thus, in our recent mechanistic studies on the partial selective hydrogenation of acrolein toward the unsaturated alcohol propenol over Pd model surfaces, we were able to demonstrate that the surface modification with a dense overlayer of organic ligands, particularly, oxopropyl species, turns the Pd(111) surface 100% selective toward the desired hydrogenation of the C= =O bond. [19][20][21][22] In contrast, on Pd nanoparticles lacking this ligand-overlayer, only minor amounts of propanal resulting from the undesired hydrogenation of the C= =C bond were detected.…”

“…Finally, electron bombardment is realized by applying high voltage onto the sample via Ta wire which is pressed against the adaptor (10), see also Figs. 8(b) and 8(c) using Mo screws (19). The latter are electrically insulated from the chamber by hat-shape ceramic washers (20).…”