Chemical poisoning of Ni/MgO catalyst by alkali carbonate vapor in the steam reforming reaction of DIR-MCFC

Abstract

Chemical poisoning of Ni/MgO catalyst was induced by hot alkali carbonate vapor in molten carbonate fuel cell (MCFC), and the poisoned (or contaminated) catalyst was characterized by TPR/TPO, FTIR, and XRD analysis. Carbonate electrolytes such as K and Li were transferred to the catalyst during DIR-MCFC operation at 650 degrees C. The deposition of alkali species on the catalyst consequently led to physical blocking on catalytic active sites and structural deformation by chemical poisoning. TPR/TPO analysis indicated that K species enhanced the reducibility of NiO thin film over Ni as co-catalyst, and Li species lessened the reducibility of metallic Ni by chemical reaction with MgO. FTIR analysis of the poisoned catalyst did not exhibit the characteristic v(1)(D-3h) peaks (1055 cm(-1), 1085 cm(-1)) for pure crystalline carbonates. instead a new peak(1120 cm-l) was observed proportionally with deformed alkali carbonates. From XRD analysis, the oxidation of metallic Ni into NixMg1-xO was confirmed by the peak shift of MgO with shrinking of Ni particles. Conclusively, hot alkali species induced both chemical poisoning and physical deposition on Ni/MgO catalyst in DIR-MCFC at 650 degrees C.