Study Of LDHs Derived Ni-Al Nanosheets Array Catalysts For Enhancing Hydrogen Production From Glycerol Steam Reforming

Hydrogen is abundant,green,low-carbon,and widely applicable,and is hailed as the"green clean energy of the 21st century."Currently,nearly 96%of global H₂ comes from traditional fossil fuels,inevitably leading to issues such as non-renewable resources and greenhouse gas emissions.Glycerol,as a major byproduct in the production process of biodiesel,has a significant yield（1 ton of glycerol per 10 tons of biodiesel）,and the market has been in a state of oversupply,with a large portion of crude glycerol being underutilized.The conversion of glycerol into H₂ through steam reforming not only solves the issue of glycerol surplus but also helps alleviate the dependence on fossil fuels for hydrogen production,making it a research hotspot in the field of hydrogen production.Nickel-based catalysts can effectively promote the breaking of C-C,O-H,and C-H bonds in glycerol molecules,while exhibiting high activity in the water-gas shift reaction,which is crucial for improving glycerol conversion,H₂ purity,and yield.However,the high reforming reaction temperature and the excessive aggregation reaction of cracked carbon fragments at the active sites make nickel-based catalysts prone to high-temperature sintering and surface carbon deposition,leading to a decrease in activity or even deactivation.In this paper,layered double hydroxides（LDHs）are used as catalyst precursors.Through the unique structure and functional characteristics of array catalysts,a series of Ni-Al nanosheet array catalysts（NiAl/NA）are in-situ constructed on a foam nickel substrate using a hydrothermal method.The performance of NiAl/NA catalysts in glycerol steam reforming for hydrogen production and the reaction mechanism are studied.The main research contents are as follows:（1）The hydrogen production reaction network of glycerol steam reforming was systematically analyzed.Based on the principle of minimizing Gibbs free energy,Aspen Plus software was used to calculate the product composition of the glycerol steam reforming process.The effects of reforming reaction temperature,glycerol concentration,and reaction pressure on gas-phase products such as H₂,CO₂,CH₄,and CO were investigated.Additionally,the response surface method with central composite design was employed to optimize the glycerol steam reforming process.（2）Ni-Al catalysts derived from LDHs were prepared using the urea hydrolysis method（NiAl-urea）and Na OH co-precipitation method（NiAl-Na OH）to obtain catalysts with different morphologies.XRD,SEM,N₂ adsorption-desorption,and other characterization techniques were utilized to characterize the crystal structure and microstructure of the catalysts.The influence of the preparation method on the performance of Ni-Al catalysts for glycerol steam reforming was studied,considering gas-phase product yields,relative contents,and glycerol gas-phase conversion rate.For the NiAl-urea catalyst,further optimization was carried out regarding the reforming reaction temperature and glycerol concentration.Additionally,a dual-functional catalyst,NiCaAl,with CO₂ adsorption capability was introduced into the NiAl-urea catalyst to investigate its performance in glycerol cracking reforming with in-situ CO₂ absorption for hydrogen production.（3）Ni-Al nanosheet array catalysts（NiAl/NA）derived from LDHs were in-situ synthesized on a foam nickel substrate using a hydrothermal synthesis method.The effects of the precursor Al³⁺addition ratio,crystallization temperature,and crystallization time on the composition,morphology,and pore structure of NiAl/NA catalysts were investigated using XRD,SEM,N₂ adsorption-desorption,and other characterization methods,elucidating the growth process of the array structure.The performance of NiAl/NA catalysts obtained under different preparation conditions in glycerol steam reforming was studied,with gas-phase product yields,relative contents,and glycerol gas-phase conversion rate as evaluation indicators,focusing on key structural factors such as nanosheet size and arrangement density.The optimized NiAl/NA catalyst structure was further explored,studying the effects of reforming reaction temperature and glycerol concentration on gas-phase product formation to determine favorable process parameters.（4）NiAl powder catalyst（NiAl-powder）was prepared using the urea hydrolysis method without the substrate.A comparative study was conducted between NiAl-powder and NiAl/NA catalysts,investigating the effects of array construction on the crystal phase composition,morphology,elemental composition,pore structure,and metal electronic structure of the catalysts using XRD,SEM（line scan）,EDS,BET,XPS techniques.The reaction stability of NiAl-powder and NiAl/NA catalysts was studied.SEM,TG-DTG,and Raman characterization techniques were employed to study the morphology,type,and content of surface carbon on the catalysts after reaction,and DFT theoretical calculations were combined to reveal the mechanism of surface carbon formation on the catalysts.