Monte Carlo simulations for the productivity and order of the PROX/copper-ceria catalyst reaction with different superficial %Cu are made. The results are correlated with the behavior of the different surface species (CO, H, O, OH, vacancies) during the process. Among other results, an inversion is seen of the production of CO2 with respect to that of H2O with the increase of %Cu, a positive order for CO2 with at low C-CO, and with CO2 if it is low, a positive order for H2O with CO2 only if % Cu is high, and zero order with C-H2 in all cases. (C) 2016 Elsevier B.V. All rights reserved.