The paper considers the model system of exothermic catalytic selective and complete conversion reactions, occurring according to the scheme A + m[B] double right arrow C + [(.)], C + [B] double right arrow D + [(.)], B + [(.)] double right arrow [B], where A and B initial reagents, C desired product (of selective conversion), D undesirable by-product (of complete conversion), [B] reagent B, chemisorbed at the catalyst surface, [(.)] vacant catalyst active site. Numerical simulation of the system behavior in fixed adiabatic catalyst bed showed that being compared to steady-state regimes it is possible to significantly improve the desired product yield and catalyst unit productivity by application of nonstationary regimes, based on periodical, separated in time, feeding of reagents A and B. The most interesting results were obtained for process performance in "reversed heat wave" mode, when temperature front of reaction is moving upstream the flow of the reaction mixture. Such operation regime is characterized with significant decrease of maximum catalyst temperature, therefore, expanded possibility to increase inlet concentration of reagents and with increased selectivity of conversion into target products. (c) 2004 Published by Elsevier B.V.