Microcalorimetric measurements were made of the interaction of hydrogen, ethene, isobutene and isobutane at 300 K with silica-supported Pt, Pd, and PtSn catalysts. The initial heats of hydrogen adsorption on silica-supported Pd and Pt are 104 and 95 kJ/mol, respectively. The presence of Sn decreases the saturation uptake of hydrogen on the PtSn sample. The initial heats of ethene interaction with Pd/silica and Pt/silica are 170 and 145 kJ/mol, respectively. The presence of Sn decreases the initial heat to 115 kJ/mol on the PtSn sample. The initial heats of isobutene interaction with silica-supported Pd and Pt are 160 and 190 kJ/mol, respectively. The presence of Sn decreases the initial heat to 125 kJ/mol on the PtSn sample. It appears that ethene and isobutene adsorb dissociatively on silica-supported Pd and Pt to form alkylidyne species at 300 K, with an average strength of carbon-metal bonds for these species near 230 kJ/mol. Ethene and isobutene adsorb on silica-supported PtSn to form di-sigma- and pi-bonded alkene species at 300 K, with an average strength of carbon-metal bonds for these species near 190 and 130 kJ/mol, respectively. Isobutane appears to adsorb dissociatively on a small number of sites on silica-supported Pd and Pt, and this dissociation is also inhibited by Sn on PtSn samples.