Base treated aluminas exhibit improved CO2 capacity over untreated aluminas. Base treated aluminas prepared by physically mixing alumina and base during forming have (1) a higher surface area, (2) less hydrothermal aging, (3) improved CO2 capacity and (4) lower cost than base treated aluminas produced by aqueous impregnation. A method for removing at least CO2 and water from a gas stream includes providing an adsorbent formed from a process comprising physically mixing activated alumina solids and solid salts of alkali metals, alkaline earth metals or ammonium ion; and contacting the gas stream with the adsorbent.