The influence of acidity of carbon nanofibre-supported palladium catalysts in the hydrogenolysis of hydroxymatairesinol
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Catalysis Letters, Vol. 113, Nos. 3–4, February 2007 (Ó 2007) DOI: 10.1007/s10562-007-9020-1
The influence of acidity of carbon nanofibre-supported palladium catalysts in the hydrogenolysis of hydroxymatairesinol Heidi Markus,a Arie J. Plomp,b Pa¨ivi Ma¨ki-Arvela,a Johannes H. Bitter,b and Dmitry Yu. Murzina,* a
Laboratory of Industrial Chemistry, Process Chemistry Centre, A˚bo Akademi University, Biskopsgatan 8, FI-20500 Turku, Finland b Department of Inorganic Chemistry and Catalysis, Utrecht University, P.O. Box 80083, Utrecht, 3508 TB, The Netherlands
Received 15 October 2006; accepted 1 December 2006
The lignan hydroxymatairesinol (HMR, extracted from Norway spruce knots) was hydrogenolysed to matairesinol (MAT) over palladium supported by carbon nanofibres (Pd/CNF) in 2-propanol at 70 °C under hydrogen flow. The influence of support acidity on the activity and the selectivity to MAT was studied. The acidity of the Pd/CNF catalyst was varied by heat-treatment at different temperatures in nitrogen flow. The catalysts were characterized by transmission electron microscopy (TEM), inductively coupled plasma emission mass-spectrometry (ICP-MS, metal content), H2-chemisorption (dispersion, metal particle size), and titration using NaOH. A more acidic support material was more active and selective to the desired product MAT. The major byproduct was 7-iso-propoxymatairesinol resulting from a reaction of the solvent with HMR over the acid sites on the support. The hydrogenolysis of HMR to MAT requires both the presence of metal and acidity. KEY WORDS: Carbon nanofibres; palladium; acidity; hydrogenolysis.
1. Introduction Precious metals on activated carbon supports are commonly used catalysts in fine chemical production. The main advantages using carbons as support materials are that they are relatively inert and inexpensive, they are stable in both acidic and basic media, and the precious metals supported on them can easily be recovered [1–4]. Activated carbon is produced from different kinds of raw materials, for example wood, coal, coconut shell, and peat are frequently used, but also synthetic polymers or petroleum processing residues can be utilized [1]. Commercial carbon-supported metal catalysts sometimes exhibit large batch-to-batch variations in performance which is, at least partially, due to natural variations in the starting materials [2]. To avoid this problem, synthetic carbon can be used as support material. Carbon nanofibres (CNF) are such a material. They are grown by decomposition of carbon-containing gases on small metal particles. The material obtained is of high purity after the growth catalyst has been removed [5]. Reviews concerning CNF [6,7] describe the synthesis and properties of these materials in detail. Three common types of CNF are often described: ribbon-like (tubes), where the carbon layers are parallel to the growth axis, platelet, where the layers are perpendicular to the growth axis, and herringbone nanofibres, having *To whom correspondence should be addressed. E-mail: dmurzin@abo.fi
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