On the adsorption of formaldehyde at high temperatures and zero surface coverage

The adsorption of formaldehyde (HCHO) at very low vapor concentration (zero surface coverage) is studied on several carbon materials by using inverse gas-solid chromatography (IGC). The adsorption process is carried out in the Henry's law region. Therefore, the specific retention volumes, V-s, allow the determination of the standard enthalpy of adsorption, Delta H degrees(A), using the linear relationship between In V-s vs 1/T. Nevertheless two linear plots are obtained for the adsorption of HCHO on these carbon materials. Several experiments have been designed in order to determine the physical meaning of these Linear plots. The general conclusion is that they are produced by a temperature-dependent mechanism which allows the adsorption to occur in smaller pores at lower temperatures and in larger ones at higher temperatures.