Pd-based Catalysts Supported On NH₂-SBA-15 For Hydrogen Evolution From Formic Acid

Hydrogen is considered to be a most promising alternative to fossil fuels due to its high efficiency,non-pollution,and reproducibility.However,the safe and efficient hydrogen storage techniques are the main obstacles for the large scale applications.Formic acid?FA,HCOOH?,a major product of biomass processing with high energy density,nontoxicity,and excellent stability at room temperature,has recently attracted tremendous research interests for H2 storage and generation.In the presence of suitable catalysts,FA can be catalytically decomposed to H2 and CO2 at room temperature.However,CO can also be generated through a dehydration pathway,which is easy to poison the catalysts,leads to deactivation of the catalyst.Therefore,the keys to the practical application of this system is to develop and synthesis of high selective,active,stable catalyst.In this thesis,we have designed and prepared a series of NH2-SBA^-15 supported Pd-based catalysts for hydrogen evolution from FA.The main research contents are as follows:?1?The silane coupling agent APTES was used to functional SBA^-15 to obtain the amine-founctional SBA^-15(NH2-SBA^-15),and then Pd nanoparticles immobilized on the NH2-SBA^-15 have been synthesized by a facile impregnation method(Pd@NH2-SBA^-15).The characterized TEM results showed that ultrafine Pd nanoparticles with a small size of around 2.1 nm are well dispersed on the NH2-SBA^-15 support.Compared to the Pd/SBA^-15 and the support-free-Pd nanoparticles,the as-synthesized Pd@NH2-SBA^-15 catalyst shows much higher catalytic activity towards the dehydrogenation of FA.The initial turnover frequency?TOF?is measured to be 1745 h^-1 at 298 K,and the H2 selectivity reaches 92%.We also studied the effect of the amount of amino groups and the amount of sodium formic on the catalytic dehydrogenation of formic acid.?2?In order to further improve the activity of catalyst,PdIr alloy nanoparticles supported on NH2-SBA^-15 has been successfully synthesized by impregnation method.The results show that Ir@NH2-SBA^-15 has no activity for hydrogen evolution from FA,while the PdIr@NH2-SBA^-15 exhibits excellent catalytic activity.The initial TOF was measured to be 6650 h^-1 at 318 K,and the H2 selectivity reaches 100%.To the best of our knowledge,this is the first report that Ir-based heterogeneous catalyst can be used to catalyze the dehydrogenation of formic acid to hydrogen.Based on the PdIr@NH2-SBA^-15,we introduced Au into PdIr alloys.The obtained tri-metallic PdAuIr@NH2-SBA^-15 catalyst shows enhanced catalytic activity for hydrogen evolution from FA due to the synergy between the metals,giving the initial TOF up to 18043 h^-1 at 318 K,which is higher than most of the reported catalysts.