Resistance of Ni/pyrochlore catalysts to H2S and NH3 in toluene steam reforming

Catalytic steam reforming is an attractive route to remove biomass tar generated during gasification process. However, gaseous impurities such as H₂S and NH₃ are usually present in the syngas produced, which may poison the catalyst. Herein, reaction characteristics and mechanism of biomass tar steam reforming using toluene as a model compound were studied with a promising type of Ni/A₂B₂O₇ catalysts in the presence of H₂S or NH₃. The results show that both H₂S and NH₃ can lead to the poisoning of catalysts with a gradual reduction in catalytic performance, but Sr doping in catalyst support of pyrochlore can significantly slow down this kind of deactivation. Characterization tests show that H₂S is adsorbed on catalyst surface to form sulfur-containing substances, and NH₃ competes with toluene reforming for activity Ni sites. In contrast, Sr doping could enhance oxygen mobility, which alleviates the consumption of adsorbed oxygen during poisoning, and promotes sulfur oxidation and coke gasification.