Calorimetry of CO adsorption was used for the first time to study the surface properties of alumina-supported molybdenum phosphide (MoP/Al2O3). To increase the dispersion of MoP active sites, the sample was prepared by novel citric acid-temperature programmed reduction (CA-TPR) method. Fourier transform infrared spectroscopy (FT-IR) of CO adsorption confirmed the formation of MoP by CA-TPR method. The calorimetry results proved that the novel method increased the amounts of active sites and led to the formation of a highly dispersed alumina-supported MoP, but the adsorption heat and the active sites distribution were not much affected by the preparation method. Furthermore, the energetic distribution of active sites depended on the MoP loading. (c) 2006 Elsevier B.V. All rights reserved.