Study On Mn-promoted Ni-Al-O Catalyst And Ba-Co-O Catalyst For Hydrogen Production Via Auto-thermal Reforming Of Acetic Acid

Hydrogen,as a clean and renewable energy source,has received much attention for its high combustion efficiency and can be generated from various raw materials.Among those raw materials,biomass oil obtained from fast pyrolysis of renewable biomass is a promising candidate,while auto-thermal reforming?ATR? is an effective hydrogen-generation route with low energy cost.In this paper,acetic acid?HAc?,a nonflammable component in biomass oil,was studied as the raw material for auto-thermal reforming,while Mn-promoted catalysts were developed for hydrogen generation.However,deactivation in the ATR of HAc could occur due to oxidation,sintering,and carbon deposition.In the current work,characterizations of XPS,TPR,SEM and XPS were employed;based on the mechanism of ATR of HAc,gasification of coke was proposed and effect of structure on catalytic performance was investigated.Two types of Mn-promoted catalysts have been designed and investigated as followed:Series of Ni-Mn-Al-O catalysts,NM-xA?x=0,0.25,0.5 and 1,where x represents mole ratios of Al/?Ni+Mn??,were prepared by co-precipitation method.The performance of ATR of HAc showed that the stability and activity of the NM catalyst(Ni Mn_5.88O_11.32±?) was decreased after 10 hours.Over the NM-0.5A catalyst(Ni_0.39Mn_1.61AlO4.31±?),a significant improvement in catalytic performance was observed:the acetic acid conversion reached 100%,the hydrogen yield was near 2.7mol-H₂/mol-HAc and remained stable in 50-h activity test.Characterizations of XRD,H₂-TPR,BET,XPS,and SEM were carried out as well.With strong-interaction between manganese and nickel,a spinel structure of NiMn₂O₄ was formed with dispersed Ni particle;meanwhile,oxygen vacancies were found and could be beneficial to oxygen transfer.After reduction,a thermal-stable spinel structure of MnAl₂O₄ with MnO was formed and restrained the growth of Ni particle;meanwhile,oxygen transfer from lattice to surface was promoted by Mn O_x spieces and oxygen vacancies,and surface oxygen was beneficial to gasification of carbon.As a result,deactivation by carbon deposition and sintering was restrained.Series of Ba-Co-Mn-O catalysts,BC-xM?x=1,2 and 4,where x represents mole ratios of Mn/Ba?with a perovskite structure,were prepared by the sol-gel method.The results of ATR of HAc showed that there was a 10-h startup period over the BC-1M catalyst(Ba_0.43Mn_0.43Co_0.14O1.29±?),and the conversion of acetic acid gradually increased from 80% to 99%,while the hydrogen yield gradually increased from the 1.1 mol-H₂/mol-HAc to 2.4 mol-H₂/mol-HAc and remained stable.For the BC-2M catalyst(Ba_0.29Mn_0.58Co_0.13O1.36±?)with more Mn doped,a better activity performance obtained:the conversion of acetic acid was around 100%,and there was low selectivity of by-products including methane,acetone and other hydrocarbons;meanwhile,the hydrogen yield reached 2.6 mol-H₂/mol-HAc.The results from characterizations indicate that the Ba Mn O₃ perovskite and Mn₃O₄ were formed in the BC-2M catalyst oxide with specific surface area at 43.6m²/g.In addition,the Co particles were doped into the Mn₃O₄ lattice and formed defect sites,which facilitated the transfer of O* species.After hydrogen reduction,strong interaction between Ba particles and the Co particles was found in the perovskite-derived BaCoO₂,which improved the dispersion of Co metal.During the ATR reaction,Ba particles within BaCoO₂ were favour to form a thermally stable species of BaCO₃,and Co particles were further reduced to Co⁰ with a smaller particle size and dispersed in BaCO₃.As a result,sintering and oxidation of metal Co were effectively suppressed.