A method that combines finite volume method (FVM) and grand canonical Monte Carlo (GCMC) method is proposed to investigate the direct air capture of low concentration CO2 by 5A zeolites in an adsorption bed of a space shuttle. In the FVM, the multicomponent Langmuir model and linear fitting formula are used to calculate saturation adsorption capacities and adsorption heat at macro-scale level, respectively. The GCMC method is used to obtain the parameters of the multicomponent Langmuir model and linear fitting formula at micro-scale level. The combined method overcomes the shortcomings of the saturation adsorption capacities and adsorption heat restricted by experiments or empirical formulas. The effects of inlet velocity, particle size, and porosity on heat and mass transfer in the adsorption bed are predicted. The saturation adsorption time for N-2 is faster than that for CO2. The competitive adsorption process between CO2 and N-2 is divided into three stages, namely, primary, intermediate, and saturation stage. The location of temperature difference peak between solid and gas phase moves toward the outlet of the adsorption bed with increasing velocity, porosity, adsorption time or decreasing particle size. An adsorption bed with high inlet velocity and porosity and small particle size is recommended to achieve improved performance. (C) 2018 Elsevier Ltd. All rights reserved.