We performed calculations based on density functional theory and experimental studies to investigate the confinement effects in carbon nanotubes.We found in the confined interior cavities of carbon nanotubes,the dissociative binding energies of CO,N2,and O2 are always weaker with respect to those on the same catalysts(Fe,FeCo,RhMn,and Ru)supported on the exteriors.The weakened binding energies can be used to successfully interpret the pervious experimental observations in redox reactions,as well as being capable of predicting the activities of these catalysts in conjunction with theoretical microkinetic models.Our experimental results have also validated these predictions in two probe reactions,namely,the Fischer-Tropsch and ammonia syntheses.The present work demonstrates that a confined environment can result in significant strains on encapsulated catalysts and change their electronic structures.Therefore,confinement effects exhibit the capability of tuning the intrinsic activity of catalysts.