Study On The Preparation Of MCM-41 Supported Metal Catalyst And Its Performance Of Hydrolyzing Ammonia Borane To Hydrogen

Hydrogen energy has the characteristics of clean,efficient,and eco-friendly,and is considered an ideal alternative to traditional fossil fuels.Ammonia borane is one of the best candidates for hydrogen storage materials,and its hydrolysis rate is closely related to the catalyst.In the preparation and catalytic reaction of metal catalysts for the hydrolysis of ammonia borane,metal nanoparticles（NPs）tend to agglomerate and fall off,which greatly reduces their catalytic activity and stability.In order to overcome this problem,Pt/MCM-41,PtNi/MCM-41,and Ni PCe O_x/MCM-41 catalysts were prepared by equal volume impregnation using mesoporous MCM-41 molecular sieves with large specific surface area,ordered pore structure,and high stability as supports,and the following research was conducted on them separately.（1）Pt/MCM-41 catalyst was prepared using an incipient wetness impregnation combined with hydrogen reduction strategy,and the effect of Pt loadings on the hydrogen production rate of ammonia borane hydrolysis was investigated.The results showed that Pt NPs were highly dispersed on MCM-41 support,improving catalytic activity and stability.The optimal loading amount of Pt is 1.5 wt%,and the initial conversion frequency（TOF）value and reaction activation energy（Ea）of the ammonia-borane hydrolysis reaction at 298 K reach 294 mol_H2(mol_Cat.·min)^-1 and 53.55 k J·mol^-1,respectively.After 5 cycles,the 1.5Pt/MCM-41 catalyst retained 70.4%of its initial catalytic activity.（2）PtNi/MCM-41 catalyst containing non noble metal Ni was prepared to reduce the loading of precious metal Pt,and the effects of Pt/Ni molar ratios on the hydrogen production rate of ammonia borane hydrolysis were investigated.The results indicate that the introduction of Ni can form smaller particle size PtNi alloys with Pt,and it is highly dispersed on MCM-41 support.The electron transfer in PtNi alloy NPs accelerates the cleavage of the B-H bond in NH₃BH₃ molecule,thereby promoting the hydrolysis of ammonia borane.When Pt:Ni=0.4:0.6,the catalytic performance is optimal,with TOF and Ea values of 939 mol _H2(mol _Cat.·min)^-1 and 34.50 k J·mol^-1 at 298K,respectively.After 5 cycles,the Pt_0.4Ni_0.6/MCM-41 catalyst retained 81.2%of its initial catalytic activity.（3）To further reduce the cost of catalyst preparation,Ni PCe O_x/MCM-41 catalysts without precious metals were prepared,with significantly higher catalytic activity than Ni/MCM-41,Ni P/MCM-41,and Ni Ce O_x/MCM-41 catalysts.XRD,TEM,XPS and other characterization results show that the introduction of Ce O_x can reduce the crystallinity of Ni P NPs and help to provide more active site for adsorption of NH₃BH₃and H₂O molecules,while the electron transfer from Ce to Ni and P atoms can increase the electron density of Ni P NPs and promote the breaking of B-H bonds.The TOF and Ea values of Ni PCe O_x/MCM-41 catalyst for ammonia borane hydrolysis reaction at 298K are 47 mol_H2(mol_Cat.·min)^-1 and 35.86 k J·mol^-1,respectively.After 5 cycles,the Ni PCe O_x/MCM-41 catalyst retained 76.6%of its initial catalytic activity.