Precise Design Of Metal-Oxide Interfaces Of Pt,Pd Catalysts And Their Catalytic Performance

Oxide supported metal nanocatalysts are one important category of heterogeneous catalysts,widely applied to the industrial,energy and environmental catalysis.Previous research demonstrated that metal-oxide interfaces play an important role in catalytic reactions.Therefore,rational design and optimization of metal-oxide interfaces seems to be the effective method to synthesize the advanced catalysts.However,traditional wet chemical method cannot realize the precise regulation of the metal-oxide interface at the atomic level,leading the limited catalytic performances.Atomic layer deposition technique(ALD),owing to the molecular self-limiting surface reaction,can precisely tailor the coverage,dispersion and thickness of oxides on noble metals at the atomic level,which achieved the optimized catalytic performance.In this study,we combined the ALD technique with traditional wet chemical method.Nine permutations of SiO2 supported bilayered metal-oxide subnano clusters catalysts were successfully synthesized.In addition,we also prepared the Pt1-Ni1(OH)x dimeric catalysts.The above mentioned catalysts exhibit excellent catalytic properties in oxidation,hydrogenation and dehydrogenation reactions.The details are shown as follows:Firstly,we developed a new strategy to atomic-level precise fabrication of bilayered Pt-CoOx subnano clusters catalysts.The strong electrostatic interactions between 3-aminopropyltriethoxysilane and PtClx?-and Pt-CoOx interactions promoted to form bilayered Pt-CoOx structure.The HAADF-STEM and XAFS suggested that the planar subnano Pt-CoOx clusters are nearly a bi-layer structure,where two dimensional(2D)Pt subnano clusters were dispersed on the support,and the highly dispersed CoOx species were deposited on the 2D Pt clusters,forming enriched Pt-CoOx interfaces.In preferential oxidation of CO in H2,the resulting materials showed exceptional catalytic performance,by achieving 100%CO conversion and selectivity in the temperature range from 25 to 140?,far superior to traditional 3D Pt-CoOx nanoparticles and Pt1/Co3O4 single atom catalysts.DRIFTS and XPS results showed that the Pt in 2D Pt-CoOx subnano clusters are more electron deficient compared with traditional 3D Pt-CoOx nanoparticles,resulting in the weaken of the CO adsorption on Pt.Therefore,weaker CO adsorption and enriched metal-oxide interfaces of 2D Pt-CoOx clusters might be the intrinsic reasons of the enhancement of catalytic performance.Furthermore,on the basis of the synthetic strategy of bilayered Pt-CoOx catalyst,we successfully synthesized bilayered Pd-NiOx subnano catalyst.The HAADF-STEM and XAFS suggested that the planar subnano Pd-NiOx clusters are nearly a bi-layer structure,consisting of approximately one atomic layer of Pd and one NiOx layer on top.DRIFTS exhibited that the electron transfer direction between Pd-NiOx was reversed as decreasing the dimension of Pd clusters from 3D to 2D.In selective hydrogenation of acetylene,the bilayered Pd-NiOx catalyst achieves outstanding catalytic activity,selectivity and stability compared with traditional 3D Pd-NiOx nanoparticles and Pd1Ag single atom alloyed catalysts.In addition,we generalize this methodology,and other seven kinds of bilayered metal-oxide clusters catalysts were prepared(Pt-NiOx?Pt-CuOx?Pt-ZnO?Pd-ZnOx?Ir-NiOx?Ir-CuOx and Ir-ZnO).The HAADF-STEM confirmed the formation of bilayered metal-oxide structures.Finally,we prepared C3N4 supported Pt1-Ni1(OH)x dimeric catalysts by ALD.The HAADF-STEM and XAFS further confirmed the existence of Pt1-Ni1(OH)x diatomic structure.According to DRIFTS and XPS results,we found obvious electron transfer between Pt single atom and atomically dispersed NiOx species,indicating the formation of unique dimeric metal-oxide interfaces.In hydrolysis of ammonium borane,the Pt1-Ni1(OH)x dimeric catalysts showed extremely high catalytic activity,with a specific rate of 1444 molH2 molpt-1 min-1,about 13 times higher than that of Pt1 single atom catalyst.The isotope kinetic experimental results indicated that the dissociation of water is the rate determining step.The synergistic effect between Pt atoms and Ni1(OH)x atoms greatly improved the catalytic activity.