The separation of binary mixture representatives of natural and landfill gases by selective adsorption using adsorbent porous clay heterostructures has been investigated. Using Wyoming clay as a starting material, the solids are prepared by the gallery-templated approach from the polymerization of two silica sources, tetraethoxysilane (TEOS) and phenyltrietboxysilane (PhOS), at several molar ratios. In this way, the surface chemistry and the porosity characteristics of the samples are modified. The adsorbents presented specific surface areas up to 634 m(2) g(-1), micropore-size distributions with maxima near to 0.6nm, thermal stability up to 400 degrees C and also hydrophobic characteristics. The selectivity for the separation of various binary mixtures such as CO2/CH4, CO2/C2H6 and C2H6/CH4, estimated by a methodology based on the determination of the Gibbs free energy, is discussed. (c) 2007 Elsevier B.V. All rights reserved.