The state of metallic Pt supported on alumina-magnesia hydrotalcite was investigated using diffuse reflectance FT-IR spectra of adsorbed CO and terminal Pt hydrides formed upon hydrogen dissociative chemisorption on metal at room temperature. On hydrotalcite surface metallic Pt exists in three different forms, such as neutral and negatively charged metallic particles as well as slightly negatively charged clusters encapsulated between layers of support : Negative charging on Pt particles results in decrease of singleton frequency of linearly adsorbed CO by 70 cm(-1) and frequency of Pt-H bond vibration by 50-100 cm(-1). It was also established that negatively charged Pt is less sulfur resistant than neutral Pt particles.