High catalytic performance of Fe-Ni/Palygorskite in the steam reforming of toluene for hydrogen production

Abstract

The inexpensive and abundant material, palygorskite, was used as a promising catalyst support to prepare Fe-Ni/Pal catalysts. Catalytic steam reforming of toluene as a biomass tar model compound over these catalysts was investigated in a fixed-bed reactor under different parameters, including reaction temperatures and S/C molar ratios. The stability and lifetime of Fe3Ni8/Palygorskite catalyst was evaluated under optimal conditions and its kinetic parameters were determined as well. The fresh and used catalysts were characterized using X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), transmission electron microscopy (TEM), and Raman spectra. The results showed that the Fe3Ni8/Palygorskite catalyst with high dispersion was successfully prepared and exhibited superior catalytic performance compared with those of the monometallic catalysts (Fe3/Palygorskite and Ni8/Palygorskite) and the bare Palygorskite. Increasing the reaction temperature from 500 °C to 700 °C was beneficial for the toluene conversion and gaseous yields. The catalytic activity of Fe3Ni8/Palygorskite varied distinctly with the increase of S/C molar ratio and reached maximum at the the S/C molar ratio of 1.0. The apparent activation energy of 41.55 kJ mol−1 and the pre-exponential factor of 1.35 × 103 m3 kg−1 h−1 were obtained for Fe3Ni8/Palygorskite in kinetic studies under optimal reaction conditions, respectively. The carbon deposition analysis of the used catalysts revealed that the formation of graphitic carbon rather than amorphous carbon was the main reason for the deactivation of Fe3Ni8/Palygorskite catalysts. When ceased the injection of steam into the reaction system, the graphitic carbon would be accelerating formed on the surface of the Fe3Ni8/Palygorskite and decreased its catalytic activity for toluene conversion. But owing to the water gas shift reaction, the catalytic activity of Fe3Ni8/Palygorskite seemed to recover gradually to its optimum.