Synthesis Of Nanocatalysts For Catalytic Hydogen Release In Ammonia Borane Hydrolysis

Hydrogen has attracted considerable attention as a clean energy with abundant storage capacity and high energy density.The secure storage and transport of hydrogen is the most difficult challenges for the hydrogen technology.Ammonia borane?AB?,due to its high hydrogen storage capacity,is considered to be one of most promising candidates for hydrogen storage materials.Because of the special tubular structure,excellent physicochemical properties and cost advantages,natural nano-halloysite mineral shows potentials as the substitute of various synthetic nanomaterials and the support of transition metal nanocatalysts.In order to improve the surface properties of halloysite nanotubes?HNTs?,the surface modification is generally carried out.Mesoporous carbon spheres?MCSs?are a new class of non-silicon-based mesoporous materials with large specific surface area and pore volume and are expected to get important applications in catalyst supports.We modified the surface properties of HNTs by simple efficient high polymer modification in the present study.And then,we investigated the performance of modified HNTs and MCSs as the supports of bimetal catalyst for hydrogen production from ammonia borane.The main contents and results of the present study are as follows:?1?Preparation of Cu-Co/PDDA-HNTs nanocatalysts and study of their performance for ammonia borane hydrolysisBimetallic Cu-Co nanocatalysts on poly?diallyldimethylammonium chloride?functionalized halloysite nanotubes?Cu-Co/PDDA-HNTs?by a deposition-reduction technique at room temperature.The results revealed that the PDDA coating with thickness of?15 nm could be formed on the surface of HNTs,and the existence of PDDA was beneficial to deposit Cu and Co nanoparticles?NPs??².2 nm?with high dispersibility on the surface.The as-prepared nanocatalysts?Cu₁-Co₁/PDDA-HNTs?exerted satisfactory catalytic activity with a high TOF value of 30.8 mol_H2/(mol_CuCouCo min)for the dehydrogenation of AB.These values were considerable compared to many reported literatures.?2?Preparation of AgPd/PDA-HNTs nanocatalysts and study of their performance for ammonia borane hydrolysisAgPd alloy nanoparticles?NPs?supported on halloysite nanotubes?HNTs?coated polydopamine?PDA?synthesized by one-pot hydrothermal route.The charactation results showed that AgPd alloys with high dispersibility immobilized on the surface of HNTs.AgPd/PDA-HNTs nanocomposites were effective catalysts for the hydrolysis of AB at room temperature,and the reaction was completed within 160seconds using Ag₃Pd₂/PDA-HNTs as catalysts,with a high TOF value of 90 mol_H2/(mol_AgPdgPd min).After the sixth cycle,Ag₃Pd₂/PDA-HNTs catalyst retained 72%of its initial activity and 100%conversion.?3?Preparation of PdNi/MCSs nanocatalysts and study of their performance for ammonia borane hydrolysisPdNi bimetal NPs were anchored in the MCSs through a simple co-reduction process.MCSs were prepared by“silica-assisted”method,phenolic resols as a polymerprecursor,silicateoligomersasaninorganicprecursorand cetyltrimethylammonium bromide as a template.Characterization techniques revealed the average diameter of the synthesized MCSs were 170 nm and bimetallic PdNi NPs with a mean size of 3.2 nm were successfully anchored into the mesoporous carbon spheres?MCSs?.PdNi/MCSs catalysts was proven to be responsible for the efficient production of hydrogen from AB,providing a high TOF value of 120 mol_H2mol_H2/(mol_PdNidNi min)at room temperature.The superior catalytic activity of the catalyst could be ascribed to the highly dispersed PdNi NPs and the synergistic electronic interactions between palladium and nickel.The large pores and high specific surface area of the MCSs contributed to the mass transportation by reducing and smoothing the diffusion pathways,leading to high catalytic activity.