In this investigation, a reactor model for prediction of the deactivation behavior of MTO's porous catalyst in a fixed bed reactor is developed. Effect of coking on molecular transport in the porous structure of SAPO-34 has been simulated using the percolation theory. Thermal effects of the reaction were considered in the model and the temperature profile of the gas stream in the reactor was predicted. The predicted loss in catalyst activity with time-on-stream was in very good agreement with the experimental data. The resulting coke deposition and gas temperature profiles along the length of reactor suggested a reaction front moving toward the outlet of the fixed bed reactor at the operating experimental conditions of 1 h(-1) and 723 K for methanol space velocity and inlet temperature, respectively. Effects of space time, coordination of Bethe network, and effective diffusivity of component in reaction mixture on the reactor performance are presented. (C) 2011 Elsevier Ltd. All rights reserved.