Removal of Adsorbed Organic Impurities from Surface of Spent Catalysts Pd/Activated Carbons
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Removal of Adsorbed Organic Impurities from Surface of Spent Catalysts Pd/Activated Carbons LIDIA DABEK Swietokrzyski University of Technology, 25-534 Kielce, Poland ANDRZEJ SWIATKOWSKI∗ AND JERZY DZIADUSZEK Military Technical Academy, 00-908 Warsaw, Poland [email protected]
Abstract. Influence of method and conditions of spent Pd/AC catalyst regeneration on its catalytic activity was studied. It has been stated that supercritical fluid extraction (CO2 ) followed by heating in hydrogen atmosphere is an effective method of that catalyst regeneration. The results of FTIR and XPS investigations indicate that regeneration of a spent Pd/AC catalyst, irrespective of the reaction in which it has been used, should be based on the complete removal of by-products and cleaning the catalyst surface as well as on restoring the original form of the palladium. Proposed in this paper procedure i.e. SFE (CO2 ) and heating in H2 fulfils both above mentioned conditions. Keywords: 1.
Pd/activated carbon catalyst, spent catalyst, regeneration
Introduction
Owing to their porosity, developed specific surface and capability of modeling both the structure and chemical constitution of a surface, activated carbons are widely used as adsorbents, catalysts and catalysts supports where metals or metal compounds constitute the active phase (Rodriguez-Reinoso, 1995; Radovic and Rodriguez-Reinoso, 1997; Radovic and Sudhaker, 1997; Rodriguez-Reinoso, 1998). The metals most commonly supported on carbon are those of Groups 8–11 of the Periodic System (Fe, Co, Ni and Cu Groups), although the largest volume corresponds to platinum, palladium, rhodium, ruthenium and iridium (Auer et al., 1998), as shown in the brochures of the more important catalyst manufacturers e.g. (Alfa Aesar Johnson Matthey, 2003–2004). Of the great number of catalysts prepared on supports such as activated carbon are those whose active phase consists of palladium scattered over the carbon surface (Pd/AC) (Gurrath et al., 2000; Kang et al., 2002; K¨ohler et al., 2002; Stiles and ∗ To
whom correspondence should be addressed.
Koch, 1995). Catalysts of the palladium-activated carbon type are used commercially in numerous processes (Maulijn et al., 2000; Nagaoasa and Aoyama, 2001; Van de Sand et al., 1998). Among typical examples are the liquid-phase hydrogenation reactions catalyzed by carbon supported palladium catalysts. The aim of the present work was to assess the possibility of regeneration of spent Pd/AC catalysts.
2.
Materials and Methods
The following Pd/AC catalyst samples were investigated: a commercial Aldrich 10 wt% Pd catalyst, indicated as CC, a spent catalyst subjected to supercritical fluid (CO2 ) extraction (Dabek et al., 2002), indicated as SC/SFE, and a spent catalyst subjected to organic solvents (acetone, methanol, benzene) ultrasonic extraction SC/OSE. The spent Pd/AC catalyst (SC) consists of mixed CC catalyst samples used in the hydrogen reduction of various organic substances. In our previous work (Dabek et al., 2002) the spent Pd/AC catalyst subject
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