In this theoretical work the CO2 conversion into methanol in both a traditional reactor (TR) and a membrane reactor (MR) is considered. The purpose of this study was to investigate the possibility of increasing CO2 conversion into methanol with respect to a TR. A zeolite MR, able to combine catalytic reactions with separation properties of zeolite membranes, which allows only vapours to permeate, is considered. A mathematical model is used to simulate a traditional chemical reactor: a comparison among the model results and literature experimental data confirmed the validity of the model. Afterwards, the model is used to predict the behaviour of a zeolite MR in terms of both CO2 conversion and methanol selectivity. The results show that it is possible to obtain both higher CO2 conversion and methanol selectivity with respect to a TR operating at the same experimental conditions. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.