In situATR-FTIR analysis of the CO-tolerance mechanism on Pt2Ru3/C catalysts prepared by the nanocapsule method

Abstract

The CO-tolerance mechanism of monodisperse Pt₂Ru₃ (d = 3.6 nm) nanoparticles supported on high surface area carbon black prepared by the nanocapsule method (n-Pt₂Ru₃/C) was investigated by in situ attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy in 1% CO (H₂-balance)-saturated 0.1 M HClO₄ at 25 and 60 °C. For the n-Pt₂Ru₃/C catalyst, the band intensity ratio of bridged CO to linear CO, I[CO_B]/I[CO_L] was smaller and the band intensity of CO on the Ru site I[CO-Ru] was larger than those of a commercial catalyst, c-Pt₂Ru₃/C, at nearly identical CO coverage θ_CO. This suggests that the Pt and Ru atoms were exposed on the n-Pt₂Ru₃ surface more uniformly (well-alloyed) than those of c-Pt₂Ru₃. The initial CO adsorption rate on n-Pt₂Ru₃/C was lower than that on c-Pt₂Ru₃/C. At high θ_CO, the hydrogen oxidation reaction (HOR) current on n-Pt₂Ru₃/C decreased significantly with increasing I[CO-Ru], while the c-Pt₂Ru₃/C exhibited a higher HOR current with a lower I[CO-Ru]. It was found that the CO-tolerance on n-Pt₂Ru₃/C was greatly improved by treatment in H₂ at 200 °C and was superior to c-Pt₂Ru₃/C at an apparent θ_CO of 0.95. Because the hydrogen adsorption sites were found to be increased and I[CO-Ru] was suppressed markedly, the formation of a Pt-rich surface with an underlying Pt–Ru alloy was found to be essential to maintain the electronic modification effect of Ru, which helps to preserve HOR active sites by weakening the bond strength of Pt-CO.