Catalyst performance changes induced by palladium phase transformation in the hydrogenation of benzonitrile

The influence of hydrogen pressure ( pH 2) on the performance of a γ-alumina-supported Pd catalyst was studied for the multiphase selective hydrogenation of benzonitrile to benzylamine and byproducts. The transformation to Pd β-hydride ( β-PdH) above a threshold pH 2 of 10 bar induces a change in tu...

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Bibliographic Details
Published in:	Journal of catalysis Vol. 274; no. 2; pp. 176 - 191
Main Authors:	Bakker, Jasper J.W., Neut, Anne Geert van der, Kreutzer, Michiel T., Moulijn, Jacob A., Kapteijn, Freek
Format:	Journal Article
Language:	English
Published:	Amsterdam Elsevier Inc 09-09-2010 Elsevier Elsevier BV
Subjects:	Adsorption modes Benzonitrile Benzylamine Catalysis Catalysts Chemical reactions Chemistry Condensation Exact sciences and technology General and physical chemistry Hydrogenation Hydrogenolysis Palladium Palladium β-hydride Phase transitions Selective hydrogenation Surface intermediates Surface physical chemistry Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry Toluene Adsorption modes Selective hydrogenation Surface intermediates Hydrogenolysis Palladium β-hydride Toluene Palladium Benzylamine Condensation Benzonitrile Binary compound Hydrogen Alcohol Activation Selectivity Hydrogenation Supported catalyst Phase transformation Alkanol Platinoid Hydrocarbon Transition metal Propanol Substrate Heterogeneous catalysis Adsorption Benzenic compound Frequency Alumina Lattice structure Catalyst Palladium hydride
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Summary:	The influence of hydrogen pressure ( pH 2) on the performance of a γ-alumina-supported Pd catalyst was studied for the multiphase selective hydrogenation of benzonitrile to benzylamine and byproducts. The transformation to Pd β-hydride ( β-PdH) above a threshold pH 2 of 10 bar induces a change in turnover frequency and byproduct selectivity. The influence of hydrogen pressure on the performance of a γ-alumina-supported palladium catalyst was studied for the multiphase selective hydrogenation of benzonitrile to benzylamine and byproducts. Semi-batch experiments of benzonitrile hydrogenation in 2-propanol were performed with hydrogen pressures between 2.5 and 30 bar, at a constant temperature of 80 °C. The intrinsic property of palladium to absorb hydrogen into its lattice structure has a strong influence on activity and selectivity. The transformation to stable palladium β-hydride above a threshold hydrogen pressure of 10 bar induces a persistent change in turnover frequency and byproduct selectivity. The turnover frequency increases from 0.32 s −1 to a maximum of 0.75 s −1 at this threshold pressure and decreases to 0.25 s −1 with increasing hydrogen pressure. The palladium β-hydride phase suppresses the hydrogenolysis to toluene changing the selectivity from 6.5% to 2.0% and increasing the selectivity of the condensation to dibenzylamine from 1.6% to 2.7%, attributed to modified electronic interactions between catalyst and substrates. The selectivity to the desired product benzylamine is always high and increases with hydrogen pressure from 92.7% to 95.3%. The palladium catalyst state is mainly determined by the activation or operational hydrogen pressure, whichever was the highest, if the activation pressure was above 10 bar.
ISSN:	0021-9517 1090-2694
DOI:	10.1016/j.jcat.2010.06.013