Highly Dispersed Co/C For Catalytic Steam Reforming Of Corncob Tar At Low Temperature

The generation of tar is one of the bottlenecks in the large-scale industrial application of biomass gasification.The development of a catalyst with high activity,low cost,and high stability at low temperature is the key to meet low-temperature catalytic removal of tar.Lignite has high organic oxygen content and low calorific value.It is not suitable for fuel but is a natural ion exchange material.Using modified lignite as the carbon precursor,the Ni/C catalyst prepared by the ion exchange method has excellent performance for catalytic reforming of tar at medium temperature（650 ^oC）,but its stability is poor.Although the Ni-Co/C bimetallic catalyst showed certain activity at low temperature（450 ^oC）,the poor dispersion of Co limited its catalytic performance.In this paper,lignite was used as the carbon precursor,and Co was introduced into the lignite by ion exchange method to prepare a highly dispersed Co_0.1/C catalyst.A two-stage falling-bed quartz reactor was used to evaluate the catalytic performance of Co_0.1/C and Ni_0.1/C which prepared by the same method in the steam reforming of the tar model compound（toluene）at low temperature（400-500 ^oC）.Then compare the catalytic performance of Co_0.1/C,Ni_0.1/C,and traditional tar cracking catalyst（Ni/zeolite and commercial Ni/Al₂O₃）in the steam reforming of the real tar.And finally,explore the catalytic mechanism of high-dispersion Co/C for low temperature and high-efficiency tar removal.In this study,the Shengli lignite（SL）was modified with hydrochloric acid and hydrogen peroxide,and then Ni and Co were loaded on the acid-washed and oxidized lignite（OXAWSL）by ion exchange.Ni/C and Co/C catalysts were prepared after carbonization.In the toluene steam reforming experiment,the activity of Co_0.1/C is higher than Ni_0.1/C at 450 ^oC and a water-to-carbon ratio（S/C）of 3.4,the maximum toluene conversion is 96.3%.The lifetime and stability evaluation of Ni_0.1/C and Co_0.1/C were carried out with at least 18 h continuous toluene steam reforming reaction.The results suggested that the activity and stability of Co_0.1/C were better;the toluene conversion was finally kept at 85%after 30 h.The Apparent activation energy（E_a）was calculated by kinetic study.Co_0.1/C.Co_0.1/C with a lower E_a（22.0 k J/mol）is corresponding to its excellent performance at such moderate conditions.The characterization results suggested that the high activity and stability of Co_0.1/C resulted from the smaller particle size（5.6 nm）and the higher dispersion（12.3%）of Co.Meanwhile,the oxygen-philic properties of Co also help to improve the carbon deposition resistance of Co_0.1/C.Finally,Ni_0.1/C and Co_0.1/C were used in the steam reforming of real biomass tar and compared with the Ni/zeolite and commercial Ni/Al₂O₃,it was found that Co_0.1/C also has the best catalytic performance.At 450 ^oC and S/C of 3.4,the relatively high yield of H₂（42.59 mmol/g-biomass）was produced.The Co/C catalyst prepared from lignite as carbon precursors and low-temperature tar cracking process developed in this research can provide theoretical and technical support for the large-scale industrial utilization of biomass pyrolysis and gasification.