The membrane reactor is a promising device to produce pure hydrogen and enrich CO2 from syngas. To figure out the detailed reaction phenomena of high-temperature water gas shift reaction (WGSR) in a Pd-based membrane reactor, a computational fluid dynamics (CFD) model is developed to simulate the chemical reaction where the feed gas temperature and steam-to-CO molar ratio (S/C ratio) are in the ranges of 400-700 degrees C and 1-3, respectively. The predictions suggest that the WGSR proceeds from kinetically controlled reaction to thermodynamically governed one when the feed gas temperature increases. The CO conversion at high temperatures can be improved up to 83% when the membrane is in the reactor compared to that without the membrane. This is mainly attributed to the intensification of the membrane's permeance with increasing temperature, even though high temperatures disadvantage CO conversion. The analysis also reveals that the breakthrough in the thermodynamic limit of CO conversion can be achieved in the membrane reactor when the feed gas temperature is higher than 500 degrees C. The CO conversion in the membrane reactor can be higher than the thermodynamic equilibrium up to 61%. (C) 2017 Elsevier Ltd. All rights reserved.