Preparation And Catalytic Performance Of Carbon-based Metal Catalysts Derived From Biomass Waste

China is rich in biomass resources.Biomass waste has the characteristics of high carbon content,renewable,abundantly available at a low cost.Biomass waste after effective treatment can be turned into treasure and avoiding the adverse impact on the climate caused by its simple incineration.At present,the optimization of the preparation process and the improvement of the performance of carbon-based catalysts require comprehensive assessments based on specific catalytic reactions.In this work,we screened different biochar preparation and activation methods for catalytic applications of carbon-based materials.The optimization of the biochar preparation process,the effective dispersion of metal nanoparticles on carbon supported catalysts and the adsorption,tar cracking and photocatalytic degradation of organic compounds over carbon-supported photocatalysts,are successively evaluated.The detail studies are as follows:（1）Optimization of preparation process of activated carbon:activated carbon was prepared by microwave-assisted pyrolysis and activation under CO₂atmosphere using furfural residue as the biomass feedstock,which is industrial and agricultural biomass waste.The effects of different pretreatment methods,activation temperature,activation time and impregnation ratio on the yield,quality and adsorption properties of activated carbon were studied.The results show that chemical reagents（such as KOH）can effectively improve the pore structure and adsorption properties of activated carbon.Furfural residue activated carbon with high adsorption capacity was obtained with relatively low impregnation ratio（KOH:FR=0.5）,which avoided the extensive use of chemical reagents and reduced the preparation cost.Moreover,compared with the preparation conditions of activated carbon（MWAC-O）（850℃/60 min）,MKAC-O was prepared with lower temperature and short time（800℃/20 min）which also has higher specific surface area and pore structure.The mesoporous volume of MKAC-O is greater than 48%,which has a positive effect on the adsorption of MB molecules.In the activation mechanism,the consumption of carbon atoms by CO₂and KOH,high microwave heating rate（249.6℃/min）and heating uniformity are the direct reasons for the high specific surface area and large pore volume of MKAC.Based on the above analysis,it is a feasible method to prepare activated carbon by physicochemical activation coupled with microwave-assisted heating from furfural residue.This method achieves the preparation goal of obtaining porous high-adsorption activated carbon with low dosage of chemical reagents,and provides an optimization attempt for the subsequent activation and modification technology of biomass carbon materials,which has potential industrial application prospects.（2）Preparation and application of carbon-based iron-supported catalysts:Using forest biomass waste,sawdust,as raw material,carbon-supported iron catalyst was prepared by loading metal ions to biomass by iron salt impregnation method.Biochar-based iron-loaded nano-catalysts are then directly synthesized by microwave pyrolysis and applied for catalytic cracking of naphthalene,a biomass tar model compound.Three pretreatment methods（acid-washed impregnation,ultrasonic impregnation,and hydrothermal impregnation）combined with microwave pyrolysis were used to synthesize carbon-supported metal catalysts and their performances were compared.Carbon-based iron catalyst with highly dispersed Fe nanoparticles（average particle size≤11.3 nm）was obtained by ultrasonic pretreatment and hydrothermal pretreatment.Secondly,Sample NWC750 prepared at 750°C formed more metal iron（Fe⁰）and ferrous iron than the catalyst prepared at500°C.In addition,the catalyst samples synthesized by ultrasonic pretreatment（USC750）and hydrothermal pretreatment（HTC750）showed not only excellent naphthalene cracking efficiency（94%-100%）after 2 h reaction at low space velocity but also exhibited good performance at high space velocity,with tar conversion>90%.USC750 and HTC750 also showed good catalytic stability after 4 h reaction at 750°C.In addition,HTC750 was highly resistant to coke deposition(0.004 g_cg^-1_Cath^-1).The strong reducing ability of Fe⁰in the carbon-based iron-supported catalyst promotes the cleavage of the benzene ring to form small molecules.The oxidized active sites were reduced to low-valent iron particles due to the existence of the carbon support.The low-valent iron particles continue to participate in the reaction,which maintains the high catalytic activity of the catalyst.In conclusion,ultrasonic pretreatment and hydrothermal pretreatment combined with microwave pyrolysis were found to be a simple and effective technique to synthesize carbon-based metal nano catalysts,with good dispersion of Fe⁰.And the catalyst demonstrated high catalytic efficiency and durability,as well as good catalytic activity.（3）Preparation and application of carbon-based Ti O₂photocatalysts:activated carbon prepared from furfural residue was combined with ultrasonic and hydrothermal treatment to disperse metal particles,carbon-supported Ti O₂photocatalysts were successfully prepared by ultrasonic-assisted sol-gel treatment（USG）and solvothermal treatment（ST）combined with microwave-assisted heating（MH）.The catalytic performance of the catalysts was evaluated by the adsorption and catalytic degradation of tetracycline（TC）under UV illumination.The results show that the average size of Ti O₂particles of carbon-based photocatalysts is between 9 nm and 11 nm.Organic carbon and AC in the catalyst play a positive role in reducing the band gap.Compared with Ti O₂-STM,the conduction band potential of Ti O₂@AC-STM was significantly reduced,which promoted the generation of photogenerated electrons.Moreover,the Ti-C and Ti-O-C in Ti O₂@AC significantly facilitated the transport of photogenerated electrons from Ti O₂to the activated carbon,promoting the efficient separation of photogenerated electrons and holes.Under UV irradiation,Ti O₂@AC-STM and Ti O₂@AC-USGM exhibited removal efficiencies of 88.0%and 75.7%in a near-neutral p H environment,significantly better than other catalysts reported under similar conditions.The carbon-based photocatalyst could be used in a wide p H range（6-9）.The degraded TC solution is close to neutral,which greatly avoids the further acid-base adjustment of wastewater.In addition,The reaction rate constant of Ti O₂@AC-STM under visible light illumination is 9.5×10^-3min^-1,which is 1.6 times that of Ti O₂-STM and 3.2 times that of commercial Ti O₂-P25.Finally,Ti O₂@AC-STM can be recovered by simple sedimentation from the treated wastewater,avoiding the complex and expensive separation process.Ultrasonic-assisted sol-gel treatment and solvothermal treatment combined with microwave heating to optimize the preparation process can achieve high efficiency and low energy consumption for biochar-based catalyst preparation.The prepared photocatalysts have great potential applications for removing TC pollutants under UV light and visible light.In summary,the above research provides new insights for biomass waste utilization,the activation and functionalization of biochar,and the synthesis and application of carbon-supported nanocatalysts.