Features of hydrogen and deuterium ignition over noble metals at low pressures

Abstract

Hydrogen and deuterium combustion over Rh, Ru, Pd and Pt wires at total pressures up to 200 Torr and initial temperatures up to 500 °C is investigated in order to establish the temperature dependencies of autoignition limits over noble metal surfaces and to indicate the governing factors of gas ignition by a catalytic surface. It was found that Rh, Ru and Pd surfaces treated with 2H2 + O2 ignitions manifest the defects in the form of openings, which are located on surface defects. It was shown that before ignition, the catalytic wire is not heated up uniformly; and initial centers of the ignition occur.It was shown that Rh is the most effective catalyst of 2H2 + O2 ignition, the lowest ignition temperature over Rh coated Pd wire (Rh/Pd) was 210 °C, for Ru/Pd and Pd −300 °C, for Pt wire −410 °C at total pressures less than 200 Torr. A hysteresis phenomenon was observed over Ru/Pd, Pt and Pd wires; namely the ignition limit value measured over the wire when increasing temperature from a state of no ignition, is higher than the value measured when decreasing temperature from a state of autoignition. It was shown that Rh is the most effective catalyst of 2D2 + O2 ignition, in this case the lowest ignition temperature over Rh coated Pd wire (Rh/Pd) was 100 °C. It is more accurate to speak about ignition over noble metals hydrides/deuterides; thus, the lowest ignition limit of 2D2 + O2 over rhodium deuteride was 100 °C; thus, D2 is more flammable than H2 over Rh and Pd. The results obtained indicate the existence of a kinetic inverse isotope effect, which affects the reactivity of MeH and MeD, where Me =Rh, Pd.