The partial oxidation of n-butane to maleic anhydride (MA) in a solid electrolyte membrane reactor was studied in three different operation modes: electrochemical membrane reactor (EMR), cofeed membrane reactor (CR), and mixed-feed membrane reactor (MMR). The EMR operation exhibited lower selectivity to MA but higher conversion of oxygen than the CR operation. The electrochemical oxygen pumping in the MMR operation led to decrease in the MA selectivity compared to the CR operation. By means of comparing the three operation modes, the electrochemically pumped oxygen was found to be more reactive but less selective to MA than gas-phase oxygen, which is directly related to the different reaction mechanisms between the CR and EMR operations. The butane oxidation occurred in the EMR involved not only the same catalytic reaction mechanism as in the CR but also an electrocatalytic reaction. A simplified catalytic and electrocatalytic reaction-mechanism scheme was proposed for the butane oxidation carried out in the EMR. (c) 2006 The Electrochemical Society.