Heterogeneous quenching of O2(1g) molecules in H2:O2 mixtures

Abstract

Quenching of O2(1g) molecules both in the gas phase and on a reactor surface has been investigated in binary mixtures of hydrogen and oxygen by using the fast-flow quartz reactor and infrared emission spectroscopy. Rate constants of the O2(1g) deactivation by H2 and O2 at room temperature have been determined to be (1.5±0.5) 10-18 cm3 s-1 and (1.6±0.2) 10-18 cm3 s-1, respectively. Heterogeneous quenching of O2(1g) on quartz walls has been studied both in pure oxygen and in H2:O2 mixtures. A model of O2(1g) heterogeneous quenching in binary mixtures has been developed and has allowed us to describe all observed features of singlet oxygen kinetics. Active surface complexes formed by `chemisorbed' atomic oxygen and `physadsorbed' molecules of O2 and H2 are assumed to be responsible for the O2(1g) heterogeneous deactivation. It has been shown that the higher rate of O2(1g) quenching in pure oxygen is connected with a quasi-resonant transfer of the O2(1g) electronic excitation to physadsorbed oxygen molecules. The observed effect of the wall passivation by hydrogen is conditioned both by the absence of the similar resonance in the hydrogen surface complex and by the higher bond energy of H2 in this complex. Bond energies of O2 (3750±450 K) and H2 (4050±450 K) in the surface complexes have been determined from the model parameters by fitting calculations to experimental results.