Confined Catalysis Over Metal Nanocatalysts With Two-dimensional Material Shells

It has been demonstrated that the catalytic performance of a metal catalyst can be influenced by particle size,morphology and composition.Furthermore,the catalyst activity can be modulated by construction a suitable microenvironment around the catalysts active site.Now,we construct an interface structure by two-dimensional overlayers and enhance the catalytic activity,selectivity and stability by changing the catalysts microenvironment through the confinement effect between the overlayer and particle surface.we suggest an novel route to design Pt@C and Ni@h-BN core-shell catalysts and focus on the influence of the confinement effect to the catalytic performance.CO oxidation,syngas methanation and hydrogen oxidation reaction are used as probe reaction.The main results are summarized as follows:1.Pt@C core-shell nanostructures having few-layer graphitic layers encapsulated on Pt NPs have been prepared by CVD process using a growth temperature of 450 ?.We demonstrated the promoting effect of graphitic overlayers on metal-catalyzed reactions in the supported nanocatalysts.CO oxidation over the Pt@C/SiO2 catalysts presents a lower apparent activation energy than the pure Pt/SiO2 catalyst.The TOF of the Pt@C/SiO2 catalysts at 100 ? is three times higher than the Pt/SiO2.CO pulse chemisorption and in-situ IR results confirm that CO oxidation reaction happened on the Pt NPs surface under the graphene covered.2.Ni nanoparticles were covered by h-BN shells with controlled thickness.In comparison with the pure Ni NPs,Ni NPs covered with few-layer h-BN shells exhibit excellent methanation activity.Furthermore,the stability of Ni catalysts has been also enhanced by the h-BN shell.Surface science measurements on h-BN/Ni(111)model surface and chemisorption results on Ni@h-BN nanocatalysts confirm the feasible CO and H2 adsorption on Ni surfaces covered with ultrathin h-BN overlayers and the methanation reactions are catalyzed by Ni surfaces under the h-BN covers.3.A non-noble metal HOR catalyst which consists of nickel cores and ultrathin h-BN shells has been made.In comparison with pure Ni NPs,Ni NPs covered with few-layer h-BN shells exhibit high HOR activity in alkaline electrolytes.The exchange current density of the Ni3@(h-BN)1/C-700NH3 sample is six times higher than the Ni/C-500NH3 sample.Characterization experiments and theoretical investigations reveal that the enhanced HOR activity is attributed to the appropriate Ni-Oad and Ni-Had interaction strength on the Ni surface under the h-BN shell.