The electrochemical promotion of the hydrogenation of CO2 on porous Ru catalyst-electrodes supported on K-beta ''-Al2O3, a K+ conductor, was investigated at temperatures 280 degrees C to 420 degrees C and atmospheric total pressure. Methane and CO were the only detectable products and the selectivity to CH4 was varied reversibly between 0.01 and 98% by varying the catalyst potential between -0.8 V and 0.4 V, which corresponds to a change in the K+ coverage on the catalyst surface between 0.32 and zero. The rate of CO formation increases monotonically with increasing K+ coverage theta(K+), and thus with decreasing potential, i.e. it exhibits electrophilic behavior, while the rate of CH4 formation is an overall decreasing function of theta(K+), i.e. it exhibits electrophobic behavior. However, for lower temperatures the methanation rate exhibits a local maximum at intermediate theta(K+) and potential values, exhibiting volcano-type behavior. This minimum shifts to lower potentials with increasing hydrogen partial pressure and increasing temperature. The results are in very good agreement with the rules of electrochemical and classical promotion. (C) 2015 Elsevier Ltd. All rights reserved.