Hydrogenolysis of methylcyclopentane was studied in the presence of supported platinum catalysts, with particle sizes between 0.9 and 2.4 nm. The distribution of ring-opening products (n-hexane, 2-methylpentane, 3-methylpentane), which are virtually the only products at 573 K, mainly depended on the platinum particle size, with no effect of the methylcyclopentane conversion. This distribution was well described by the selective or non-selective mechanisms previously proposed in the literature except for the smallest particles (d < 1.5 nm), for which a very high yield in n-hexane was observed. A simplified model was developed combining a geometric approach, for counting the fraction of accessible surface of each superficial atom whatever the Pt particle size, to the knowledge of active sites for each product formation, as determined by DFT calculation. It was demonstrated that the sites responsible for n-hexane formation are corners and some edge sites, whereas 2-methylpentane and 3-methylpentane are formed on faces and a part of the edges. (C) 2018 Elsevier Inc. All rights reserved.