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Selectivity tuning over monometallic and bimetallic dehydrogenation catalysts: effects of support and particle size

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Abstract

The efficacy of tandem dehydrogenation–condensation catalysts for the upgrade of bio-derived intermediates is largely determined by their relative (de-)hydrogenation and decarbonylation activity. Here, the effects of support and particle size of heterogeneous PdCu alloy catalysts on (de-)hydrogenation and decarbonlylation reactions were investigated using kinetic measurements, X-ray absorption spectroscopy and density functional theory (DFT). The chemical mismatch of Cu2+ with Ti4+ and Ca2+ prevents the substitution of Cu into the lattice of TiO2 or hydroxyapatite supports, and facilitates its alloying with Pd, resulting in improved selectivity for hydrogenation–dehydrogenation reactions compared to decarbonylation reactions. Based on kinetic measurements of butyraldehyde reactions over Pd and PdCu/SiO2 model catalysts, decarbonylation activity is attributed to the presence of Pd surface ensembles, while (de-)hydrogenation reactions are catalyzed by PdCu sites on the surface. This is consistent with selectivity and CO coverage trends with increasing conversion, and DFT-based microkinetic modeling. Selectivity control can also be achieved using the PdCu nanocluster size. Smaller nanoparticles favor the C–CO bond scission step of the decarbonylation reaction, due to the stronger binding of CO and alkyl species to sites of lower coordination. CO-induced segregation of reactive Pd atoms to under-coordinated step/edge sites also amplifies the geometric effect on the catalytic behavior.

Graphical abstract: Selectivity tuning over monometallic and bimetallic dehydrogenation catalysts: effects of support and particle size

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Publication details

The article was received on 30 Jun 2017, accepted on 22 Nov 2017 and first published on 22 Nov 2017


Article type: Paper
DOI: 10.1039/C7CY01306J
Citation: Catal. Sci. Technol., 2018, Advance Article
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    Selectivity tuning over monometallic and bimetallic dehydrogenation catalysts: effects of support and particle size

    K. A. Goulas, Y. Song, G. R. Johnson, J. P. Chen, A. A. Gokhale, L. C. Grabow and F. D. Toste, Catal. Sci. Technol., 2018, Advance Article , DOI: 10.1039/C7CY01306J

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