Time distribution of adsorption energies, local monolayer capacities, and local isotherms on heterogeneous surfaces by inverse gas chromatography

A new inverse gas chromatographic methodology is introduced to measure loca l (homogeneous) adsorption energies, epsilon, local monolayer capacities, c (max)*, and adsorption isotherms, theta(i)(p,T,epsilon) for probe gases on heterogeneous solid surfaces in the presence of nitrogen as carrier gas. Th e method does not depend on analytical solutions of the classical integral equation comprising the adsorption energy distribution function f(epsilon) as unknown, nor on numerical solutions and estimations from this equation, using powerful computers. It simply uses a time function of the chromatogra phic peaks obtained by short flow-reversals of the carrier gas, combined wi th the local isotherm model of Jovanovic. All three adsorption parameters e psilon, c(max)*, and theta(i)(p,T,epsilon) mentioned above can be calculate d as a function of the experimental time and refer to instantaneous equilib ration of the probe gases with the heterogeneous surface, with different ki nds of active sites i being involved at different times. The kinetic physic ochemical parameters for the adsorption phenomenon are also included for th e gas/solid systems studied, being C2H4/ZnO, C2H4/PbO, C3H6/PbO, and C3H6/C aCO3. A comparison of the adsorption energy values found for these systems with heats of adsorption reported elsewhere is impermissible, since the lat ter refer to overall values and not to local values as in the present metho d. However. some literature values seem rather comparable to the present on es.