Adsorption of supercritical carbon dioxide (CO2) on polydimethylsiloxane (PDMS), silica gel (SiO2), and Illinois No. 6 coal was compared using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy at pressures up to 14 MPa and temperatures at 40 T and 50 degrees C. Only physical adsorption of CO2 was recorded for PDMS, SiO2, and Illinois No. 6. There was no evidence of the formation of carbonic acid, bicarbonates, carbonates, or any other reaction product between CO2 and PDMS, SiO2, and Illinois No. 6 coal. Carbon dioxide adsorption on PDMS and SiO2 produced a linear isotherm while a typical Langmuir-like isotherm was observed for Illinois No. 6 coal. Attempts to measure CO2 induced swelling of the three materials was unsuccessful due to the design of the ATR-FTIR cell.