Mesoporous Silicon Supported Ultrafine Pd-based Nanocatalysts For Hydrogen Evolution From Formic Acid

Hydrogen energy is regarded as an important energy carrier to transform from fossil energy to sustainable energy in the future society.However,Technical bottlenecks in storage and transportation still limit the way that people lead to the hydrogen society.Formic acid?HCOOH,FA?,with 4.4 wt% hydrogen content,is the simplest organic acid,and can be safely handled and transported at room temperature due to its liquid phase and non-toxicity.What's more,formic acid can be regenerated by hydrogenation reaction of carbon dioxide.The key to the practical application of formic acid is to develop efficient,economical and stable catalysts for improving the kinetic and thermodynamic properties.The main research contents of this paper are as follows:Ultrafine bimetallic PdIr nanoparticles supported by amino functionalized SBA-15?SBA-15-NH₂?have been prepared by one-step reduction method.The as-prepared Pd_0.85Ir_0.15/SBA-15-NH₂ nanocatalysts has ultrafine particle size?1.1±0.4 nm?,excellent dispersion and abundant active sites.As a result,the SBA-15-NH₂ has a strong adsorption for Pd²⁺and Ir³⁺ion.The catalytic performance of the dehydrogenation of FA is improved by the synergistic effect between electrons of Pd and electrons Ir.At room temperature with sodium formate,Pd_0.85Ir_0.15/SBA-15-NH₂ exhibits 100% H₂ selectivity and conversion toward hydrogen generation from FA,and the initial turnover frequency?TOF?is measured to be 3087 h^-1.In addition,the initial TOF value reaches as high as 8248 h^-1 at 323 K.Under the same conditions,this initial TOF value is higher than that of most heterogeneous catalysts.In order to reduce the cost of the catalyst,we introduced the non-noble metal Cr.The PdCr/SBA-15-NH₂ nanocatalysts are prepared by an one-step co-reduction method.The ultrafine particle size?1.3±0.4 nm?and excellent dispersion could be attributed to the fact that amine groups have a strong adsorption for metal.At 323 K without the additives,the optimized catalyst Pd_0.8Cr_0.2/SBA-15-NH₂ achieves a very high efficiency,with of the initial TOF value of 1386 h^-1.Based on the analyses,the excellent catalytic performance the dehydrogenation of FA could be attributed to the strong interaction between metal and substrate,and the transference of some electrons from Cr to Pd and forming the rich electrons Pd sites.The ultrafine PdZr nanoparticles have been synthesized by one-step reduction method.The Pd_0.9Zr_0.1/SBA-15-NH₂ nanocatalysts show outstanding catalytic activity and 100% H₂ selectivity for formic acid dehydrogenation at room temperature without any additives,with the initial TOF of 1243 h^-1.The TOF_initial value reaches as high as3150 h^-1 at 318 K.The Pd_0.9Zr_0.1/SBA-15-NH₂ nanocatalysts show excellent recycle stability,with 100% H₂ selectivity ever after the fifth consecutive cycle.