Controllable Synthesis Of Supported Noble Metal Nanoclusters And Their Electronic Structure-Dependent Catalytic Activity For Hydrogen Production From Ammonia Borane And Formic Acid

The supported noble metal nanoclusters play an important role in the modern science of catalysis due to their outstanding catalytic performance in many primary industrial reactions.Meanwhile,with the rapid development of modern technology,people can directly observe and modulate the compositions and properties of catalysts at atomic level,and then further figure out the key factor in determining the performance of catalyst.In this thesis,three different kinds of supported noble metal nanoclusters have been prepared by changing the composition of metal nanoclusters,the kind of support and surface ligand.The impact of metal support interaction,the coordination effect and synergistic effect in determining the performance of as prepared catalysts were discussed in detail with sufficient characterization and analysis.Firstly,based on the coordination effect between N and metal cation,3aminopropyltriethoxysilane(AP)modified SiO2 supported Pt nanoclusters(AP-SiO2@Pt)with the average sizes of 1.4±0.3,2.0±0.3,2.3±0.4 and 2.8±0.4 nm were synthesized and employed on the catalytic hydrogen production from the hydrolysis of ammonia borane(AB)at 30 ?.The optimized AP-SiO2@Pt with the average Pt size of 2.0±0.3 nm showed the highest activity with TOF value of 197 molH2 molPt-1 min-1.Afterwards,AP-SiO2@Pt@NGO was developed by simply coating of nanosized graphene oxide(NGO)layers with the thickness of 1?2 nm on the surface of AP-SiO2@Pt.The AP-SiO2@Pt@NGO exhibited enhanced catalytic activity on the hydrolysis of AB,whose TOF value reached 325 molH2 molPt-1 min-1 at 30?.The improved activity can be attributed to the electron-deficient Pt nanoclusters tuned by NGO,which has been proved by XPS analysis.Secondly,the amino group functionalized support AP-SiO2@NGO-PDA was prepared using p-phenylenediamine(PDA)and AP as a superior support of ultrafine Pd clusters(APSiO2@NGO-PDA@Pd)for the dehydrogenation of formic acid(FA).The obtained catalyst with 20 wt%of AP,2 wt%of NGO,2 wt%of Pd and 12/1 of PDA/NGO mass ratio showed the highest catalytic activity and stability,with the initial TOF value of 8274 molH2 molPd-1 h-1 at 50? and 100%selectivity of H2.The detailed XPS analysis and DFT calculations proved that the terminal-NH2 of the PDA on NGO can serve as proton reservoirs with suitable binding capability towards the*H species,which promoted the dehydrogenation of the FA molecule.Further,AP-SiO2@NGO-PDA@PdAu bimetal nanoclusters were prepared for improving the catalytic efficiency based on their synergistic effect.HRTEM,XRD and in-situ CO adsorption DRIFTS results proved the formation of PdAu nanoalloy.The initial TOF values of catalysts for FA dehydrogenation follow the volcanic-type relationship with the decreased mole ratio of Pd to Au.The highest TOF value of 16647 molH2 molPd-1 h-1 was achieved when the mole ratio of Pd/Au was about 1/1 at 50?.According to XPS analysis,the binding energy of Pd0 3d5/2 decreased with the increase of Au content.It can be concluded that the appropriate tuning on the electronic structure of Pd along with the PDA ligand effect co-promoted the catalytic activity for FA dehydrogenation.