Silica supported amine materials are promising compositions that can be used to effectively remove CO2 from large stationary sources, such as flue gas generated from coal-fired power plants (ca. 10 % CO2) and potentially from ambient air (ca. 400 ppm CO2). The CO2 adsorption characteristics of prototypical poly(ethyleneimine)–silica composite adsorbents can be significantly enhanced by altering the acid/base properties of the silica support by heteroatom incorporation into the silica matrix. In this study, an array of poly(ethyleneimine)-impregnated mesoporous silica SBA-15 materials containing heteroatoms (Al, Ti, Zr, and Ce) in their silica matrices are prepared and examined in adsorption experiments under conditions simulating flue gas (10 % CO2 in Ar) and ambient air (400 ppm CO2 in Ar) to assess the effects of heteroatom incorporation on the CO2 adsorption properties. The structure of the composite adsorbents, including local information concerning the state of the incorporated heteroatoms and the overall surface properties of the silicate supports, are investigated in detail to draw a relationship between the adsorbent structure and CO2 adsorption/desorption performance. The CO2 adsorption/desorption kinetics are assessed by thermogravimetric analysis and in situ FT-IR measurements. These combined results, coupled with data on adsorbent regenerability, demonstrate a stabilizing effect of the heteroatoms on the poly(ethyleneimine), enhancing adsorbent capacity, adsorption kinetics, regenerability, and stability of the supported aminopolymers over continued cycling. It is suggested that the CO2 adsorption performance of silica–aminopolymer composites may be further enhanced in the future by more precisely tuning the acid/base properties of the support.