The effects of composition and metal particle size of platinum catalysts on ethane dehydrogenation were investigated on PtxSn100-x/Mg(Al)O (70 <= x <= 100) catalysts prepared with average particle sizes between similar to 2 and 7 nm. At high conversions, catalyst deactivation from coke formation was a strong function of particle size and Sn/Pt. Deactivation decreased significantly with decreasing particle size and increasing Sn addition. To understand the true initial activity of un-deactivated catalysts, further experiments were run at low residence time conditions to limit ethene formation. For a fixed average particle size, ethane TOF and the selectivity to ethene increased with increasing content of Sn in the PtSn particle. For Pt and Pt3Sn compositions, ethane TOF increased with increasing particle size, while the selectivity to ethene was not strongly affected. The observed effects of particle size and composition are attributed to a combination of geometric and electronic factors. (C) 2013 Elsevier Inc. All rights reserved.