Study On Ni-Mg-Cr-O And Ni/La₂X₂O₇ Catalysts For Auto-thermal Reforming Of Acetic Acid

Hydrogen is an alternative clean energy carrier to fossil energy;bio-oil obtained from biomass pyrolysis is a carbon-neutral renewable energy source,in which acetic acid?HAc?is the main component and can be used as a raw material to produce hydrogen.There are various ways for hydrogen production,and auto-thermal reforming?ATR?stands out for its reaction heat-sustainity.Ni-based catalysts present advantages in activation and conversion of HAc,but there are still deactivation issues that need to be resolved,such as oxidation,sintering,and carbon deposition.Therefore,the current work focuses on the ATR of HAc to produce hydrogen,explores the effects of different components and supports on the activity of Ni-based catalysts,and studies the conversion mechanism of HAc.Ni-Mg-Cr-O and Ni/La₂X₂O₇?X=Ce,Zr,Ti?catalysts were then prepared,and a series of characterizations were used to find the structure-activity relationship of the catalysts.Ni-Mg-Cr-O catalysts were prepared by the sol-gel method,and their catalytic activities and stability in hydrogen production from ATR of HAc were investigated as well.The results of the activity test showed that the NM1C(Ni_0.25Mg_0.75Cr O_3.5+?)catalyst produced high conversion rate of acetic acid?100%?and hydrogen yield?2.64mol-H₂/mol-HAc?during the ATR of HAc.The characterization results show that there were no significant oxidation,carbon deposition and sintering within NM1C catalyst during the ten-hour ATR process.The improved reactivity can be attributed to the factors as followed:1)High specific surface area of NM1C catalyst with mesoporous structure formed after calcination;2)Highly dispersed active sites provided by the active metal Ni with smaller particle size,which promote conversion of carbon-containing species derived from HAc and suppress formation of carbon deposits;3)Interaction of Ni Cr₂O₄/Mg Cr₂O₄ spinel and Mg?Ni?O solid solution promote resistance to sintering and oxidation of the active components during the reaction process.La₂X₂O₇?X=Ce?Zr?Ti?catalysts support were prepared by the sol-gel method,and Ni/La₂X₂O₇ catalysts were then obtained by the impregnation method.The activity and stability of the catalyst during the ATR of HAc were also investigated.The results show that the La₂Ti₂O₇ layered perovskite support possessed confinement effect on the Ni particles after activation and reduction,which stabilizes in ATR of HAc.With small particle size of Ni metal,there were more active sites,promoting the activation and conversion of acetic acid and improving the catalytic efficiency.At the same time,the higher content of lattice oxygen in the Ni/La₂Ti₂O₇ catalyst can promote the conversion of carbon-containing intermediate products derived from HAc,which plays a important role in inhibiting the formation of carbon deposits.Therefore,in the results of the activity test,the layered perovskite catalyst showed good activity and stability:the conversion of acetic acid reached 100%,and the hydrogen yield was about 2.65 mol-H₂/mol-HAc.At the same time,no carbon deposits was observed in the catalyst after the reaction.