Preparation Of Aminated Polyacrylonitrile Supported Pd-based Nanoparticles Catalysts For Hydrogen Generation From Formic Acid

Hydrogen production and storage are the hot topic in the field of hydrogen energy development.Formic acid（FA）,as the simplest and easily available carboxylic acid,has the characteristics of relatively high hydrogen content,low toxicity and easy storage,and can be decomposed into hydrogen（H₂）and carbon dioxide（CO₂）under relatively mild conditions,so it is considered as a safe and convenient hydrogen storage compound.In recent years,a varity of catalysts reported in the literatures have shown good catalytic performance for the decomposition of FA.Among them,supported palladium nanoparticles（Pd NPs）catalysts have drawn more attention due to its unusual activity and selectivity for H₂ generation.The results show that the types of supports and preparation methods have great influence on the activity and stability of Pd NPs.In order to obtain high efficient catalysts,porous materials with high specific surface area are usually used as supports,and complex preparation steps are often required under harsh conditions to achieve the control and optimization of catalyst performance.These factors lead to high cost of catalyst preparation and complex process,which are not conducive to practical application and promotion.Therefore,it is of great significance to design and prepare more efficient catalysts for FA decomposition by selecting more suitable supports and preparation methods.Based on the above situation,we here tried to use low-cost polyacrylonitrile（PAN）nanoparticles and hollow microspheres as catalyst supports.After modifying,the surface of the supports by surface amination treatment,two kinds of aminated polyacrylonitrile supported Pd NPs were prepared by impregnation reduction method.The structure and properties of the catalysts were studied by various characterization techniques,and the performance of the catalysts was investigated by FA decomposition reaction.The main research contents of this thesis are as follows:1.The coral-like polyacrylonitrile（PAN）nanoparticles（500-600 nm）were synthesized by boiling soap free emulsion polymerization of Acrylonitrile with ethyl acetate as solvent,2-methylpropionitrile as initiator.The resultant PAN was then modified with ethylenediamine（EDA）to obtain modified polyacrylonitrile（EDA-PAN）.Pd/EDA-PAN was prepared by the impregnation method and chemical reduction.Compared with the unmodified support PAN,the aminated EDA-PAN was more suitable for the preparation of Pd NPs with smaller particle size（about 1.2 nm）,which are uniformly distributed on the surface of support.The optimized Pd/EDA-PAN catalyst can efficiently catalyze the decomposition of FA to produce hydrogen without using any basic additives（promoters）.The turnover frequency（TOF）of the catalyst can reach 3989 h^-1 at 333 K,and the catalyst can be reused for many times after simple centrifuging and drying,showing very high activity and stability.The introduced amino groups play critical role in forming and stabilizing the ultra‐small Pd NPs,and may also directly participate the activation of FA,thus considerably enhancing the catalytic performance for the hydrogen production from FA.2.Polyacrylonitrile hollow nanospheres（HPAN）with average particle size of 500-600 nm were synthesized by template method.Polystyrene（PS）sphere was used as the precursor template,and polyacrylonitrile was coated on the outer surface of PS through polymeraization to form composite core-shell nanospheres PS@PAN.After that,the PS@PAN was etched by solvent to obtain HPAN.Aminated EDA-HPAN was prepared by EDA modification,and then PdCo/EDA-HPAN catalyst was prepared by impregnation reduction method.The results of catalytic reaction evaluation showed that PdCo/EDA-HPAN catalyst exhibits higher catalytic activity with TOF value of 4989 h^-1（333 K）,and even works well at ambient temperature(915 h^-1,303 K).Besides,the resultant catalyst has excellent stability and can be easily recycled after simple centrifiguation.Various characterization results demonstrated that compared with Pd/EDA-PAN catalyst,PdCo bimetallic nanoparticles have more uniform distribution and smaller particle size（about 0.81 nm）on the surface of HPAN.The enhancement of catalytic activity should be at least partially related to the hollow structure of the HPAN support,which is suitable for achiving higher dispersion of metal nanoparticles on the support.In addition,the introduction of a small amount of Co may further adjust the dispersion state and electronic density of Pd,which is conducive to the formation of Pd-based nanocatalyst with excellent hydrogen production performance.