Selective oxidation of CO on Ru/gamma-Al_2O_3 in methanol reformate at low temperatures

摘要

The preferential oxidation of CO (PROX) at low temperatures,80-120 deg C,over a Ru/gamma-Al_2O_3 supported catalyst pretreated by a low temperature reduction (LTR) process was investigated over a range of CO partial pressures and O2 excess in a realistic methanol reformate reaction environment,in the presence of CO_2 and H_2O.Based on transmission electron microscopy (TEM) imaging the LTR pretreatment,which involves reduction in pure H_2 at 150 C,does not lead to measurable particle growth (d_(Ru) = 2.5 nm),in contrast to the calcination/reduction (CR) pretreatment at 350 C used previously,which results in considerable particle sintering (d_(Ru) = 11.2nm).Kinetic parameters including the apparent activation energy (E approx 48kJ/mol),reaction orders for CO (alphaco) and for O_2 (alphaO_2) and the selectivity for CO oxidation as well as the influence of the co-reactants CO_2 and H_2O were evaluated.The results show a significant activity and selectivities of around 55-60% both in idealized reformate,in the absence of CO_2 and H_2O,and in realistic reformate,already at 80 deg C.This and the negligible activity for the reverse water gas shift and the CO and CO_2 methanation reaction under these reaction conditions make this catalyst suitable for application at low temperatures typical for operation of polymer electrolyte fuel cells (PEFCs),in contrast to the CR pretreated catalyst,where higher process temperatures are required.