Different pretreatments (wet, oxidation and complex pretreatments) were used to modify activated carbon honeycomb monolith, and the role of surface properties of support in CO oxidation over Pd/ACHM catalysts was also investigated. Pretreatment was an efficient way to introduce oxygen groups, especially by complex pretreatment. Oxygen-containing groups increased 1.7 times as much as that of original ACHM, and 86% conversion was obtained at 30 degrees C and 100% relative humidity on supported Pd catalyst prepared from modified ACHM. Oxygen-containing species on the support not only improved Pd dispersion but also affected Pd states. Compared with Pd dispersion, Pd states played a more important role in CO oxidation. The amount of low-valent Pd species (Pd-0, Pd+1) on catalyst surface was consistent with CO oxidation activity. The presence of NO caused CO oxidation conversion to decrease by 15% which was attributed to the difference between NO and CO adsorption energy on Pd surfaces confirmed by density functional theory calculation. 90 days' 1000 m(3)/h pilot experiment results showed that the catalyst exhibited high activity and stability in the presence of moisture and NOx. (C) 2014 Elsevier B.V. All rights reserved.