In situ structure–activity correlation experiments of the ruthenium catalyzed CO oxidation reaction

The complex structure–activity correlation of the CO oxidation on ruthenium has been studied in a batch reactor by using in situ surface X-ray diffraction (SXRD) and on-line mass spectrometry. Two distinct active phases are identified at higher pressures in the mbar range depending on the reaction conditions: a non-oxidic phase and a RuO2(1 1 0) layer of variable thickness ranging from 1.5 nm to 10 nm. For reaction temperatures lower than 520 K the experimental turnover frequency (TOF) numbers are shown to be almost identical for the two types of active phases. Above 520 K the RuO2(1 1 0) layer turned out to be much more active than the non-oxidic phase. Kinetic reaction experiments on the RuO2(1 1 0) phase reveal an activation energy of 78 ± 10 kJ/mol which is in perfect agreement with corresponding reactivity experiments on supported and powder RuO2 catalyst. Under oxidizing reaction conditions and high concentration of CO2 in the gas mixture, the RuO2(1 1 0) model catalyst shows reversible product-poisoning.