Synthesis of clean transportation fuels from syngas (CO + H-2) derived from coal, natural gas, and renewable biomass is an efficient method for reducing dependence on oil reservoirs, for which developing effective catalysts is significant. Co-based catalysts supported by carbon materials possess advantages such as longer lifetimes and easy handling of wasted catalysts, but increasing their activity and selectivity remains a challenge. Here we report using Cr as a promoter to enhance the CO hydrogenation process over activated carbon (AC)-supported Co-based catalysts, namely, CoxCr/AC catalysts. An almost twofold increase in activity (from 28.9% to 47.0%), accompanied by decreased CH4, olefin, and alcohol selectivity, was achieved by adding Cr, resulting in a significant increase in the yield of transportation fuel products. The results of chemisorption indicate that Cr facilitates H-2 adsorption and suppresses the formation of cobalt carbide (Co2C), forming a relative H-rich and C-lean surface chemical environment, so that the CO hydrogenation process and C-C coupling step are enhanced. Structural characterizations show that Cr exists in the form of Cr2O3 and aggregates on the surfaces of the catalysts in a highly dispersed manner at relative low loadings (<2 wt%), and that Co nanoparticles are partly covered by Cr at high loadings. We suggest that the interaction between Cr3+ and adjacent metallic Co may play a pivotal role in the elevation of CO hydrogenation activity and C5+ selectivity. (C) 2018 Elsevier Inc. All rights reserved.