Catalysis of Organic..

Kuusisto, Mikkola and Salmi 23526. Deactivation of Sponge Nickel andRu/C Catalysts in Lactose and XyloseHydrogenationsAbstractJyrki I. Kuusisto, Jyri-Pekka Mikkola and Tapio SalmiLaboratory of Industrial Chemistry, Process Chemistry Centre,Åbo Akademi University, Biskopsgatan 8, FIN-20500 Turku, FinlandCatalyst deactivation during consecutive lactose and xylose hydrogenation batchesover Mo promoted sponge nickel (Activated Metals) and Ru(5%)/C (Johnson Matthey)catalysts were studied. Deactivation over sponge nickel occurred faster than on Ru/C inboth cases. Product selectivities were high (between 97 and 100%) over both catalysts.However, related to the amount of active metal on the catalyst, ruthenium had asubstantially higher catalytic activity compared to nickel.IntroductionThe importance of catalyst stability is often underestimated not only in academia butalso in many sectors of industry, notably in the fine chemicals industry, where highselectivities are the main objective (1). Catalyst deactivation is inevitable, but it can beretarded and some of its consequences avoided (2). Deactivation itself is a complexphenomenon. For instance, active sites might be poisoned by feed impurities, reactants,intermediates and products (3). Other causes of catalyst deactivation are particlesintering, metal and support leaching, attrition and deposition of inactive materials onthe catalyst surface (4). Catalyst poisons are usually substances, whose interaction withthe active surface sites is very strong and irreversible, whereas inhibitors generallyweakly and reversibly adsorb on the catalyst surface. Selective poisons are sometimesused intentionally to adjust the selectivity of a particular reaction (2).Catalyst deactivation often plays a central role in manufacturing of variousalimentary products. Sugar alcohols, such as xylitol, sorbitol and lactitol, areindustrially most commonly prepared by catalytic hydrogenation of correspondingsugar aldehydes over sponge nickel and ruthenium on carbon catalysts (5-10).However, catalyst deactivation may be severe under non-optimized process conditions.