Metal nanoparticles have attracted much attention over the last decade owing to their unique properties as compared to their bulk metal equivalents, including a large surface-to-volume ratio and tunable shapes. To control the properties of nanoparticles with particular respect to shape, size and dispersity is imperative, as these will determine the activity in the desired application. Supported metal nanoparticles are widely employed in catalysis. Recent advances in controlling the shape and size of nanoparticles have opened the possibility to optimise the particle geometry for enhanced catalytic activity, providing the optimum size and surface properties for specific applications. This Review describes the state of the art with respect to the preparation and use of supported metal nanoparticles in catalysis. The main groups of such nanoparticles (noble and transition metal nanoparticles) are highlighted and future prospects are discussed.

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This work aims to produce triacylglycerols (TAG) containing a medium-chain fatty acid (M) at positions sn-1,3 and a long-chain fatty acid (L) at sn-2 position, i.e. TAG of MLM type, by acidolysis of virgin olive oil with caprylic (C8:0) or capric (C10:0) acids, catalyzed by 1,3-selective Rhizopus oryzae heterologous lipase (rROL) immobilized in Eupergit Ò C and modified sepiolite. This lipase was produced by the methylotrophic yeast Pichia pastoris. Reactions were performed at 25 and 40°C, for 24 h, either in solvent-free or in n-hexane media, at a molar ratio 1:2 (olive oil:free fatty acid). Higher incorporations of C8:0 (21.6 mol%) and C10:0 (34.8 mol%) into the TAG were attained in solvent-free media, at 40°C, when rROL immobilized in Eupergit Ò C was used. In organic media, at 40°C, only 15.9 and 14.1 mol%, incorporation of C8:0 or C10:0 were, respectively observed. Lower incorporations were attained for both acids (3.4-7.0 mol%) when native ROL (nROL) in both supports and rROL in modified sepiolite were used. rROL in Eupergit Ò C maintained its activity during the first four or three 23-h batches, respectively when C8:0 (half-life time, t 1/2 = 159 h) or C10:0 (t 1/2 = 136 h) were used, decreasing thereafter following a time delay model. Keywords Acidolysis Á Capric acid Á Caprylic acid Á Olive oil Á Rhizopus oryzae lipase Á Structured lipids Abbreviations FFA Free fatty acid(s) L Long-chain fatty acid(s) M Medium-chain fatty acid(s) MAG Monoacylglycerol(s) MLM Triacylglycerol(s) containing medium-chain fatty acid at sn-1 and sn-3 positions (M) and a long-chain fatty acid (L) at position sn-2 nROL Native ROL rROL Heterologous ROL ROL Rhizopus oryzae lipase SL Structured lipid(s) TAG Triacylglycerol(s) t