Study On The Hydrogen-rich Syngas Production From Biomass Pyrolysis Enhanced By Fe-based Catalyst Derived From LDH

In recent years,environmental protection has become the main melody social of economic sustainable in the progress of economic development of human society.Biomass,as the only renewable energy,can directly convert into fuel,and the add-value utilization is an important path to achieve the national strategic goal of“carbon peak”and“carbon neutral”.However,the problem of low yield,low quality of add-value products produced from the utilization of biomass,seriously restrict its large-scale utilization.The development of biomass efficient conversion technology will establish a better carbon cycle during the energy utilization.In this work,we investigated that the catalytic performance of new catalytic material for the conversion of organic volatiles generated from biomass pyrolysis progress.The design of novel pyrolysis catalyst can rise the production of high-quality hydrogen-rich syngas during the biomass pyrolysis,and provide an idea for the problems of carbon deposition and sintering inactivation of traditional catalyst.The main contents and results of this study are as follows:（1）In this study,Fe/Al catalysts derived from Fe/Al LDH synthesized by hydrothermal method and urea hydrolysis coprecipitation method,respectively,have different properties of morphology and structure.The results show that the main active phase of Fe₂O₃ of both catalysts.With the increase of synthesis temperature,the particle morphology changes to rod structure,the pore volume increase from 0.62 to 0.79 cm³/g,the average pore size increases from 8.54 to 9.97 nm,and the reduction temperature of Fe₂O₃ in Fe/Al-H is higher.Fe/Al-H showed better catalytic performance in the catalytic process,the gas yield is up to 63.69 wt.%,the liquid yield is only 13.32 wt.%,the volume concentration of syngas in the gas is 63.87 vol.%,H₂ yield is 10.18 mmol/g,which was attributed to its developed pore structure and larger pore size conducive to the exposure of more active particles,adsorption of large tar compounds secondary pyrolysis to generate more small molecule gas for Fe/Al-H catalyst.when the catalytic temperature was increased from 500 to 800℃,the gas yield increased from 49.21 to 63.69 wt.%.When the carrier gas flow rate decreased from 50 m L/min to 25 m L/min,the gas yield further increased to 66.28 wt.%,liquid yield decreased to 10.56 wt.%,and H₂+CO yield reached the highest 23.22mmol/g.The increase of catalytic temperature and the decrease of carrier gas flow rate can promote the secondary pyrolysis reaction of tar and prolong the reaction time,which is conducive to the formation of more small molecule gas.In the Fe/Al-H regeneration experiment,the gas yield and H₂ still reach 63.91 wt.%and 9.64 mmol/g after two regenerates.The yield of mmol/g and H₂ decreased by only 18%,indicating that Fe/Al-H catalyst has good reproducibility and stability.（2）We introduced the different content Ni component into Fe/Al catalyst during the progress of synthesis of Fe/Al LDH precursor to prepared a series of Fe/Ni/Al catalysts.The main mixed oxides Fe_0.99Ni_0.60Al_1.10O₄ were generated due to strong interaction between metal oxides in Fe/Ni/Al catalyst by the introduction of Ni.With the increase of Ni content,the lamellar structure is gradually normalized into flower structure,and the specific surface area（64.28-76.10 m²/g）and average pore size（8.18-10.41 nm）are also increased.In the catalytic experiment,Fe-Ni bimetal catalytic system shows better catalytic performance than single metal catalysts.With the increase of Ni addition ratio,the tar component is fully decomposed into small molecular gas in the reaction process,the total gas production increases from 985.16 m L/g to 1119.13 m L/g,and H₂ production increases from 19.36 mmol/g increased to 22.66 mmol/g,and the syngas concentration reached the highest 86.13 Vol.%on Fe Ni_1.5Al.The study on the effect of calcination atmosphere on the performance of Fe Ni_1.5Al showed that compared with N₂,in Air or N₂/H₂ atmosphere,the flower structure of the catalyst was decomposed,and the specific surface area and average pore size were reduced.The gas production efficiency of the three catalysts during catalytic pyrolysis was as follows:Fe/Ni/Al-_N2（86.37wt.%）>Fe/Ni/Al-_Air（82.05 wt.%）>Fe/Ni/Al-_N2/H2（74.15 wt.%）.With the increase of catalyst dosage,the syngas yield showed a trend of increasing first and then decreasing.Even at 1g feed,H₂+CO yield could still reach 37.71 mmol/g.In the life test,the Fe/Ni/Al catalyst activity decreased significantly after eight times of use.（3）It was found that compared with the Fe/Ni/Al catalysts supported by single carrier Mg or Al,the pore volume and average pore size of Mg/Al supported catalysts increased to 0.25 cm³/g and 26.36 nm.In addition,Fe/Ni/Mg/Al has higher gas yield（91.55 wt.%）and C,O conversion（77.40%and 103.04%）in catalytic experiments.The in-situ adsorption of Ca O on CO₂ reduced its content by about 40%,and with the increase of Ca O addition,the adsorption tended to be saturated,and the H₂ production increased first and then decreased.Under the condition of 2g Ca O addition,the H₂ production reached the highest 32.35mmol/g,equivalent to 724.78m L/g.When S/B is less than 6,H2 yield increases with the increase of water vapor addition,and the maximum hydrogen yield reaches 39.39 mmol/g.The H₂/CO ratio increases to 3.32.When S/B is higher than6,H₂ yield slightly decreases to 38.15 mmol/g.The study on the service life of Fe/Ni/Mg/Al catalyst showed that with the increase of reaction times,Ni Fe₂O₄ active phase gradually transformed into Fe Ni₃,and the flower structure gradually collapsed.After 6 reactions,H₂ production and total gas production basically stabilized at 15.03mmol/g and 818.54 m L/g.The H₂/CO ratio basically stays at 1.7.