Preparation And Catalytic Performance Of Nickelbased Cataltsts With High Dispersion And Small Size

Nickel-based catalysts have been widely employed in a broad of application,such as catalytic hydrogenation reaction,catalytic reforming reaction,partial oxidation of methane and catalytic cracking reaction because of their excellent catalytic activity.However,nickel-based catalysts have the disadvantages of sintering of Ni nanoparticles?NPs?and carbon deposition,which greatly impede the industrial application process.In recent years,Researchers have reported that the small size of Ni NPs with high dispersion are benefit to the resistance of sintering of Ni NPs and carbon deposition.Ni NPs with a high dispersion can effectively reduce the tendency of these particles to agglomerate and grow into large ones,inhibiting the catalyst sintering.In addition,small Ni particle size contributes to the improved low-temperature activity and anti-coking performance of Ni-based catalyst.Meanwhile,the dispersion of Ni NPs is closely related to the Ni particle size,which suggests that the smaller the sizethe higher the dispersion of Ni NPs.Hence,we designed a highly dispersed and small size nickel-based catalyst and studied its catalytic performance.Due to the good thermal and chemical stability,alumina is often used as a support for the synthesis of supported nickel-based catalysts.Furthermore,impregnation method is widely used in preparation of alumina supported nickel-based catalysts?Ni/Al₂O₃?.Therefore,we choosed incipient impregnation method to prepare a highly dispersed Ni/Al₂O₃ catalyst with small particle size.The main conclusions of this paper are as following:?1?The effect of impregnation solution on the performance of Ni/Al₂O₃ catalyst was investigated.40wt%Ni/Al₂O₃ catalysts with high load were prepared by incipient impregnation method with water?H₂O?,ethanol?EtOH?,N,N-dimethylformamide?DMF?as impregnated solution,respectively.The N₂ adsorption-desorption characterization showed that all three catalysts had large specific surface area.Scanning electron microscopy results showed that the impregnation solution had no effect on the morphology of Ni/Al₂O₃.The UV-visible diffuse reflectance spectroscopy indicated that DMF could inhibit the formation of nickel-aluminum spinel.The hydrogen temperature-programmed reduction results proved that it tends to form strong interaction between nickel and alumina with DMF as the impregnating solution.Moreover,according to X-ray diffraction pattern calculation results,small particle nickel-based catalyst can be prepared by DMF impregnation solution??8.3 nm?.More importantly,CO methanation performance test showed that Ni/Al₂O₃-D had better low-temperature activity and high temperature stability.The thermogravimetric and X-ray diffraction analyses of the used sample showed that Ni/Al₂O₃-D had good performance of anti-sintering and anti-coke deposition.?2?We proposed a MOF-template strategy to synthesize Ni/Al₂O₃catalyst by calcination method using nickel nitrate in DMF solution as Ni source and MIL-110?Al?as morphology template and Al source.Results of scanning electron microscopy and N₂ adsorption-desorption show that catalyst retained rod-shaped of MIL-110 with mesoporous and the surface area of Ni/Al₂O₃ was 193 m²·g^-1.The hydrogen temperature-programmed reduction results demonstrate that Ni and alumina forms strong metal-support interaction and the hydrogen temperature-programmed desorption show that catalyst surface facilitate the spillover of hydrogen,which reduce the hydrogen dissociation energy.In-situ DRIFTS shows that CO is mainly adsorbed with line type adsorption,it indicates that the catalyst has many defects.According to X-ray diffraction pattern and transmission electron microscope calculation results,the small Ni NPs are successfully prepared.Moreover,the Ni NPs are highly resistant to agglomeration and growth at high temperature.In addition,the results of UV-visible diffuse reflectance spectroscopy and transmission electron microscope that Ni NPs are highly dispersed on the support.The catalyst had good catalytic performance in selective hydrogenation of cinnamaldehyde.?3?30%Ni²⁺/MIL-110 is firstly prepared with impregnation method;and then the sample is vulcanized to obtain small particle Ni₉S₈/Al₂O₃ with dimethyl sulfide as sulfur source.The photocatalyst,CdS/Ni₉S₈/Al₂O₃,is prepared by doped CdS.Analyses of X-ray diffraction analysis and X-ray photoelectron spectroscopy show that Ni₉S₈/Al₂O₃ was formed by sulphurization.N₂ adsorption-desorption characterization showed that Ni₉S₈/Al₂O₃ had a large specific surface area and hierarchical pore structure.Ni₉S₈ has small particle size with transmission electron microscope analysis??10 nm?.Photoluminescence spectra and transient current results show that CdS/Ni₉S₈/Al₂O₃ has high photoresponse values and stability.We can deduce that Ni₉S₈ enhances photoresponsivity and separation of the photogenerated electron-hole pairs.More importantly,CdS/Ni₉S₈/Al₂O₃ with wide range of wavelength exhibits good photocatalytic activity and high stability for photochemical water splitting under visible light irradiation.