Selective catalytic low pressure hydrogenation of acetophenone on Pd/ZnO/ZnAl 2 O 4
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Catalysis Letters, Vol. 114, Nos. 1–2, March 2007 (Ó 2007) DOI: 10.1007/s10562-007-9046-4
Selective catalytic low pressure hydrogenation of acetophenone on Pd/ZnO/ZnAl2O4 Maurizio Lenarda,a,* Manuela Casagrande,a Elisa Moretti,a Loretta Storaro,a Romana Frattini,b and Stefano Polizzib a INSTM UdR di Venezia, Dipartimento di Chimica, Universita` Ca Foscari, di Venezia, Via Torino 155/B, Mestre, VE 30172, Italy INSTM UdR di Venezia, Dipartimento di Chimica-Fisica, Universita` di Venezia Ca Foscari, Via Torino 155/B, Mestre, VE 30172, Italy
b
Received 5 December 2006; accepted 4 January 2007
A PdZn alloy-based catalyst was prepared by impregnation with a Pd salt of the oxides obtained by the thermal decomposition of a Zn–Al hydrotalcite. Two samples were obtained by carrying out the reduction at 373 and 673 K, that were characterized by chemical analysis, powder XRD and TEM. The catalytic activity was tested in the low pressure hydrogenation of acetophenone. The results were compared with those obtained using a conventional palladium catalyst. KEY WORDS: PdZn alloy; bimetallics; hydrogenation; acetophenone; hydrotalcite.
1. Introduction Palladium based catalysts are largely used in the hydrogenation of organic substrates [1–4]. The properties of palladium based heterogeneous catalysts can be easily modified in order to increase selectivity by the presence of a second component and the alterations induced by alloying have been recently reviewed [2]. Various authors have observed that the catalytic behavior of Pd in a reductive atmosphere is significantly modified when ZnO is used as a support and the catalyst is pretreated at high temperature in hydrogen flow before use [5–10]. In fact, when a Pd/ZnO catalyst is reduced in hydrogen flow above 553 K a significant reduction of ZnO is observed, along with the formation of PdZn intermetallic alloys generated by the interaction of reduced Zn with metallic Pd [8–13]. The temperature of the reduction process influences the amount of metallic alloys [8–13] and consequently the Pd/PdZn ratio. Layered hydrotalcite-like anionic clays (HTlc), of general molecular formula Mx2+My3+(OH)2(x+y) Ay/n)n Æ mH2O where M2+ and M3+ are divalent and trivalent metal ions, respectively and A)n is an intercalated anion, are widely used as catalysts or catalyst precursors [14–16]. In fact, thermal treatment of HT-like materials at high temperatures produces mixed oxides of well defined and reproducible stoichiometry [14, 15]. The thermal treatment of a M2+M3+ hydrotalcite above 1173 K is known to lead to the complete decomposition of the layered structure with formation *To whom correspondence should be addressed. E-mail: [email protected]
of M 2+O and a spinel-type phase (M2+M23+O4) [14, 15]. In this study we describe the preparation of two Pd-based catalyst samples obtained by impregnation with a palladium salt the mixture of oxides generated by thermal decomposition above 1173 K of an Zn–Al HTlc. The impregnated samples were successively reduced with H2 at two different temperatures. The catalyt
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