Study On Hydrogen Production From Steam Reforming Of Acetic Acid Based On Nano-Ni/ZnO Catalysts

Hydrogen production from bio-oil steam reforming is considered to be one of the most promising technologies to achieve large-scale production of H₂from biomass,which has good development and utilization potential.Based on the existing progress and problems of domestic and foreign researchers in the theoretical basic research and technological development with bio-oil steam reforming technology,Ni-based nanoparticle catalysts were developed as the research object to conduct in-depth research on the release behavior of H₂,CO,CO₂and CH₄during the process of bio-oil-derived acetic acid steam reforming.The intrinsic relationship between the chemical composition（Ni,ZnO,Ce O₂）and structure of the catalysts and their reactivity and carbon deposition resistance was analyzed in detail,which laid the foundation for further revealing the reaction mechanism of bio-oil steam reforming for hydrogen production.Firstly,the nanorod-like ZnO supported Ni catalysts were developed by the co-precipitation coupled impregnation method.The response surface method combined with the Box-Behnken design was used to carry out the experimental study of hydrogen production by acetic acid steam reforming.The release behavior of H₂,CO,CO₂and CH₄was explored through infrared flue gas analyzers.The correlation law of nickel loading（NL）,temperature（T）,water to carbon mole ratio（SCMR）and weight hourly space velocity（WHSV）with product yields and characteristics was revealed.The second-order polynomial functions of H₂yield and potential H₂yield were established to reveal the relationships between the H₂yield and potential H₂yield responses and the individual and interdependence effects of NL,T,SCMR and WHSV with R²of 0.97.The order of the significant influence degree of variables on H₂yield from large to small was SCMR²>WHSV>WHSV²>NL²>T²>NL>T-WHSV>T,while the descending order of the substantial effects with variables on potential H₂yield was SCMR²>WHSV>WHSV²>T²>NL²>NL>T-WHSV>SCMR>T>NL-SCMR.The highest H₂yield（78.0±3.1%）and potential H₂yield（98.5±1.7%）were obtained at the optimal operating conditions of NL=21.2 wt.%,T=794°C,SCMR=2.9 and WHSV=2.5 h^-1.The comparative study on hydrogen production by acetic acid steam reforming over Ni/ZnO catalysts with three different morphologies（rod,particle and bouquet）was carried out.The chemical compositions and structural characteristics of Ni/ZnO catalysts with different morphologies before and after the reaction were investigated.The effects of Ni/ZnO catalysts with different morphologies on the compositions and contents of gas products in the acetic acid steam reforming reaction were discussed.The reaction network of acetic acid steam reforming over Ni/ZnO catalyst was proposed.The trend of H₂yield in steam reforming of acetic acid over Ni/ZnO catalysts with different morphologies was similar:which first increased continuously,and then gradually stabilized over time.The H₂yield of the acetic acid steam reforming reaction over Ni/ZnO catalysts significantly depended on the morphology in the order of rod>bouquet>particle.Compared with the particle and bouquet Ni/ZnO,the specific surface area of the rod Ni/ZnO catalyst before and after the reaction decreased from 5.4 m²/g to 2.4 m²/g with the minimal reduction of55.6%.The acetic acid steam reforming experiment was carried out under the optimal operating conditions of NL=21.2 wt.%、T=794°C、SCMR=2.9 and WHSV=2.5 h^-1to obtain the highest H₂yield of 78.0%in the rod Ni/ZnO catalyst,while the selectivity and content of H₂were 95.4%and 63.3%,respectively.Acetic acid dehydrogenated on Ni/ZnO,forming acetaldehyde,which subsequently decarboxylated to form acetone and steam reformed into CO₂and H₂.Meanwhile,active metal Ni accelerated the water-gas shift reaction.The observed catalyst deactivation was normally assigned to the coke formation produced via the methane decomposition reaction.Based on the study of the gas products release behavior in the process of acetic acid steam reforming over Ni/ZnO catalysts with precise and controllable morphology,the effects of the Ce O₂-ZnO synergism and NL with catalytic activity and catalytic behaviors were investigated.The quantitative correlation law between Ce O₂to ZnO mass ratio（CZMR）and NL and the yields of H₂,CO and potential H₂was revealed.The results show that the H₂,CO and potential H₂yields followed a Gaussian normal distribution with increasing the CZMR.An exponential function equation was established to correlate the H₂,CO and potential H₂yields with NL.As the CZMR increased from 0 to 1/3,the H₂yield increased from 57.8%to 69.4%with a growth rate of 20.1%.Further increasing the CZMR from 1/3 to 3,the H₂yield decreased by 37.6%.The CO yield showed a similar trend to H₂yield with increasing the CZMR,which first increased to a peak value,then started to decrease rapidly and finally stabilized.The yield of H₂increased significantly from 20.6%to 73.5%with the NL from 0%to 15%.Further increasing the NL from 15%to 25%,the H₂yield increasing by only 5.8%.With the CZMR of 1/3 and the NL of 15%,the selectivities of H₂and CO were as high as 91.6%and 41.3%,respectively.