Insight into one-step synthesis of active amorphous La-Co thin films for catalytic oxidation of CO

Abstract

Active amorphous lanthanum-based thin films were synthesized through one-step pulsed spray evaporation chemical vapor deposition (PSE-CVD) technique at 320 °C for CO oxidation. The obtained films were characterized in terms of phase, composition and morphological properties. X-ray diffraction (XRD) analysis revealed an amorphous nature of the deposited catalysts; and scanning electron microscope (SEM) showed a transition of morphology due to Co doping from sharp to round shaped edges. Chemical composition analysed by EDS and XPS disclose similar trends in amount of cobalt increment and lanthanum decrement. XPS deconvolution revealed pure lanthanum sample (La100) constitutes mainly of lanthanum oxide and lanthanum hydroxide; while, doping with 10% of cobalt (La90Co10) introduces formation of cobalt ions (Co3+ and Co2+) together with La3+ions and low formation of oxygen lattice. Increment of Co to 20% (La80Co20) resulted increasing of Co2+/Co3+, CO32−/OH−formation ratios and oxygen lattice (Olat) content, which may play a key role in the catalytic activity. Complete oxidation of CO was evaluated by online-FTIR. Based on light-off curves, La80Co20 catalyst exhibited the most efficient catalytic activity with T90 of 203 °C, due to increment of lattice oxygen (Olat), Co2+/Co3+ and CO32−/OH−; while, La90Co10 catalyst exhibited lowest catalytic activity which is linked to low Olat and inhibited catalytic effect of water formed at the surface. Thus, the doping strategy of La by Co at low temperature is a good approach for CO abatement. Moreover, DFT calculations demonstrated that amorphous lanthanum oxide is very feasible for CO adsorption.