Catalytic Reforming Of Bio-oil For Hydrogen Production Over Ni-based Catalysts

Hydrogen can be applied in fuel cells, and is also regarded as an importantalternative energy carrier in the future. Hydrogen can be obtained from various rawmaterials, such as natural gas, alcohols, bio-oil, and cellulose through steam reforming(SR), partial oxidation (POX) or auto-thermal reforming (ATR). Among theaforementioned routes, the production of hydrogen from bio-oil is regarded as one ofthe feasibly renewable technologies. Among the concerns involving in the reformingprocess, the coke deposition and endothermicity are the main obstacles to theindustrialization of hydrogen production via catalytic reforming process from bio-oil.In order to address the carbon deposition and endothermicity of reforming process, theATR process, in which oxygen is introduced, can balance the net heat need with arelatively high hydrogen yield by adjusting the ratio of oxygen in feed. In this study,firstly, thermodynamic analysis with Gibbs free energy minimization was performedfor aqueous phase reforming of AC as a model compounds for hydrogen productionfrom bio-oil. Secondly, Ni-Co bimetallic and dolomite-type catalysts were prepared andstudied in catalytic reforming of bio-oil for hydrogen production.Acetic acid is a representative compound of bio-oil via fast pyrolysis of biomass,and can be processed for hydrogen production via SR and ATR. Thermodynamicanalysis with Gibbs free energy minimization was performed for aqueous phasereforming of AC as model compounds for hydrogen production from bio-oil. Theeffects of the temperature (273-1273K) and oxygen/carbon ratio on the selectivity ofcarbon-containing products, formation of coke, hydrogen yield, and conversion of ACwere analyzed. Via the thermodynamic analysis, the optimal conditions for hydrogenproduction through SR/ATR were found as: reaction temperatures of750-850°C,O/C=0.1-0.3(molar) and1atm. Under the optimal conditions, all AC was consumed,the H2yield also maintained stable near2.7mol-H2/mol-AC, and coke yield was near0.2mol-C/mol-AC.In the current work, the Ni-Co (NixCo1-xMg6O7±δ, x=0~1) bimetallic catalysts wereprepared via co-precipitation and impregnation, and tested in SR of AC. The C100(CoMg6O7±δ) and N100(NiMg6O7±δ) monometallic catalysts were deactivatedobviously in SR, while the N20C80(Ni0.2Co0.8Mg6O7±δ) bimetallic catalyst performedbetter in both activity and stability: not only the conversion of AC remained stable near 100%, but also the H2yield maintained stable near3.1mol-H2/mol-AC. The results ofXRD, BET, XPS, TG and TEM indicate that the high catalytic performance of theNixCo1-xMg6O7±δcatalyst can be attributed to resistance to1) oxidation of active metalsand2) carbon deposition, and stability of structure and electronic properties.To address the carbon deposition and endothermicity of reforming process, theATR process is introduced. In the current work, the dolomite-type catalysts wereprepared via hydrothermal method, and tested for hydrogen production by ATR of AC,and characterized by XRD, TPR, BET, and SEM. With the introduction of iron, Ca(Fe,Mg)(CO3)2(Ankerite) was formed, and transformed to mixed crystals of Mg(Ni)O andFe2O3after calcination. The reaction results showed a remarkable improvement onactivity and durability in ATR process over MCNF03(MgCa0.5Fe0.3Ni0.2O2±δ) catalyst:the all AC was consumed, and the H2yield maintained stable near2.5mol-H2/mol-AC.The improved durability can be attributed to the abundant open-framework structure,stable crystal structure, and the resistance to carbon deposition and oxidation in theoxidative atmosphere of ATR.