Preparation Of Highly Coke-resistant Nickel-iron Alloy Catalysts For Dry Reforming Of Methane

Dry methane reforming（DRM）reaction is a process during which two greenhouse gases methane（CH₄）and carbon dioxide（CO₂）are used as raw materials for downstream industrial necessities from the products of carbon monoxide（CO）and hydrogen（H₂）.It has the dual benefits of resource utilization and environmental protection.The design of the catalyst is vital to obtain the excellent activity and stability.Recently,Ni-based catalysts have attracted tremendous attention and interest owing to the low price and large abundance as well as their high catalytic performance comparable to those of noble metal-based catalysts.Ni-based catalysts are prone to carbon deposition,and the formation of coke is the main origin for the deactivation of Ni-based catalysts.The design and synthesis of nickel-based bimetallic catalysts have been considered as the promising approach to prevention of coke deposition.In this work,a robust NiFe bimetallic catalyst was fabricated by the modified evaporation-induced self-assembly（m-EISA）method.With the help of systematical in situ characterizations,the effects of the alloy structure on the catalytic performance of the nickel-aluminum catalyst was explored during the DRM reaction.First,Ni/Al₂O₃and Ni₃Fe/Al₂O₃catalysts with large specific surface area(≥200 m²g^-1)and pore volume(0.8 cm^-3g^-1)were developed by the m-EISA method from a mixed solution including aluminum sol and metal nitrate in a triblock copolymer solution.The reduced Ni₃Fe/Al₂O₃catalyst exhibited superior catalytic performance than that of Ni/Al₂O₃in at low reaction temperature.Meanwhile,the reduced Ni₃Fe/Al₂O₃presented good stability at 450℃for 20 h beyond the influence of internal and external diffusion during reaction.On the basis of in situ XPS measurement,the deposited carbon species from Ni on Ni₃Fe alloy was able to be converted by FeO_xfrom the oxidation of Fe on the alloy,which promoted the gasification of carbon species and enhanced the coke resistance of Ni-based catalyst.Furthermore,the coke-resistant property of the NiFe alloy on Ni₃Fe/Al₂O₃can be further improved by the formation of Ni₃Fe alloy structure during DRM reaction.CH₄and CO₂conversions on the reaction-induced Ni₃Fe/Al₂O₃were 28%and 40%,respectively,and the H₂/CO ratio was 0.6,which was higher than those of the directly reduced Ni₃Fe/Al₂O₃.The migration of FeO_xspecies from the oxidation of Fe on NiFe alloy was observed on the spent Ni₃Fe/Al₂O₃catalysts on the basis of electron microscopy analysis.The formation of intermediate HCOO^-species was evidenced by the results from the in-situ diffuse reflection infrared Fourier transform technique.This work will provide new insights and ideas for the development of highly active and stable Ni-based catalysts.