Perovskite-type oxide catalysts for low temperature, anaerobic catalytic partial oxidation of methane to syngas

摘要

The cyclic reaction between CH_4 and O_2 over perovskite-type La_(0.8)Sr_(0.2)Fe_(0.8)Co _(0.2)O_(3-δ), La_(0.75)Sr _(0.25)Fe_(0.6)Co_(0.15)Al_(0.25)O _(3-δ) and La_(0.8)Sr_(0.2)Fe _(0.8)Co_(0.2)O_(3-δ)/γ-AlO(OH), impregnated with 0.5 wt% Rh or Pt, was studied at 873 K. Synchrotron X-ray and neutron diffraction patterns of La_(0.75)Sr_(0.25)Fe _(0.6)Co_(0.15)Al_(0.25)O_(3-)_δ proved a rhombohedral structure with Al distributed over the octahedral B-site. The oxygen non-stoichiometry (δ) was determined by thermogravimetric analysis at 958 K for pO_2 > 10~(-22) atm. High selectivity to the partial oxidation products CO and H_2 was observed when 3 - δ was lower than 2.76 and 2.78 for the mentioned oxides, with and without Al, respectively. The role of Rh relates solely to the activation of CH_4. A stable high selectivity throughout the pulse sequence was achieved when utilizing partially reduced materials. In situ synchrotron XRD proved that the oxides retained the perovskite structure during the reduction/oxidation cycle, and no phase decomposition occurred. The strong correlation between results from catalytic transient tests and thermogravimetric analysis suggests that the CO selectivity is ruled by the redox potential of the reducible oxide.