Synthesis And Catalytic Performance Of Nickel-based Bimetallic Catalysts Supported On Ordered Mesoporous Materials

The technologic route of efficiently converting methane into higher-value liquid-phase products that are easily transported have led to an increased industrial interest in the dry reforming of methane（DRM）to produce syngas.However,the nonprecious-metal catalysts used in this reaction system suffer from a stability issue caused by coke formation.The purpose of this work is to explore the highly efficient and stable nickel-based catalysts by combining the advantages of the texture properties of ordered mesoporous materials and the synergistic effect of bimetallic materials.The effect of typical ordered mesoporous materials（ordered mesoporous alumina and silica SBA-15）supported transition metal-nickel based bimetallic catalysts on the catalytic performance of methane CO₂ reforming was investigated.The pore structure,morphology and surface composition of the catalyst were analyzed by means of N₂ physical adsorption-desorption,transmission electron microscopy,X-ray powder diffraction,temperature-programmed reduction with H₂,H₂ chemisorption,X-ray photoelectron spectroscopy and thermogravimetric analysis.The effect of transition metals and mesoporous channel on the performance of the catalyst was discussed.The results of this paper are of great significance for the further study of highly efficient and stable ordered mesoporous bimetallic nickel-based catalysts.The specific contents of the study were described as follows:（1）A series of SBA-15-supported nickel-based bimetallic catalysts（M-Ni/SBA-15,M=Fe,Co,Cu and Cr）were prepared by co-impregnation method.The effects of metal doping on the physicochemical properties and catalytic properties of nickel-based catalysts（Ni/SBA-15）were investigated.Among them,Co-Ni/SBA-15 catalyst exhibited the best catalytic performance,which was due to the inherent DRM activity of Co and the increasing dispersion of Ni and inhibition its sintering with the addition of Co.And the addition of Cr led to the catalyst lose the activity of DRM.The doping of Fe affected the inherent pore structure of SBA-15,resulting in the degradation of catalytic activity and stability.Cu-Ni/SBA-15 also showed the low activity and poor stability because of the serious carbon deposition.（2）Considering the metal-support interaction can significantly affect the performance of the catalyst and the weak interaction between the SBA-15 support and the active metal,bimetallic catalysts（MNi-OMA）were prepared by doping secondary metal（M=Fe,Co or Cu）into Ni-based ordered mesoporous alumina（OMA）catalyst by evaporation-induced self-assembly method（EISA）.The results of preliminary activity investigation showed that the activity and stability of all OMA-supported bimetallic catalysts were higher than those of corresponding SBA-15-supported bimetallic catalyst,indicating that the interaction between metal and support has an important effect on the catalytic performance.Moreover,the difference in catalytic behavior of MNi-OMA catalysts in DRM was due to the difference of anti-carbon deposition behaviour.Among them,CuNi-OMA catalyst displayed the lowest reactivity and poor stability,and FeNi-OMA was catalytically active for DRM.In view of this,the effect of iron content（Fe/Ni=0.3～0.9）on the performance of x-FeNi-OMA catalyst was further studied,and the promotive effect of Fe in the process of DRM and the possible factors leading to the deactivation of FeNi-OMA catalyst were discussed.The results showed that the increase of iron content in the catalyst has an effect on the chemical properties and activity of the catalyst.The x-FeNi-OMA catalyst exhibited high specific surface area and ordered mesoporous structure when Fe/Ni￡0.7.The mesoporous structure was destroyed when the molar ratio of Fe/Ni was 0.9.According to XRD analysis,iron played an active role in DRM due to the formation of FeNi₃ alloy after the process of reduction treatment.0.7-FeNi-OMA catalyst was the most active for reforming with regard to the initial activity.By comparison of STEM-EDX results for reduced and spent 0.7-FeNi-OMA catalysts,the deactivation after 24 hours DRM reaction was associated with the dealloying of FeNi₃ under reforming conditions,rather than change in porous structure and sintering of the active metal.This study demonstrated the importance in manipulating the stability of FeNi₃ that are relevant to DRM conditions.