Macrokinetics for chemical transformation of ethylene glycol into glyoxal (including side-reactions) as well as 20 heterogeneous mathematical model were suggested. Numerical results obtained using this model were compared with the experimental data obtained at lab-scale and pilot reactor, and showed good correlation. It was shown that due to catalyst activity change it is possible to manage the process selectivity with respect to glyoxal in diffusion mode. The optimal value of catalyst activity providing the highest process selectivity can be found. (C) 2011 Elsevier B.V. All rights reserved.