The Performance And Mechanism Of Catalytic Reforming Of Methane Over Palygorskite Supported Nickel Catalysts

Carbon dioxide reforming of methane?DRM?has significant environmental benefit and shows great potential in energy utilization.DRM paves an efficient way to transform CH₄ and CO₂ into valuable syngas?H₂ and CO syngas?with the low H₂/CO ratio,which is suitable for the production Fischer-Tropsch synthesis.In addition,DRM enables to alleviate the greenhouse effect and energy shortage.Nano-minerals have widely been used as catalyst supports due to their abundant reserves,low cost and excellent physicochemical properties.Palygorskite clay is a natural nano-mineral material with special nanorod-like structure,high specific surface area,and high surface reactivity.In this dissertation,the nickel-aluminum supported catalysts and the iron-nickel supported catalysts were synthesized.The structure and physicochemical properties of the catalysts during DRM process,as well as the influencing factors,catalytic performance and the differences on the two types of palygorskite supported catalysts were investigated.The main results of this work are as follows:?1?Nickel-aluminum supported catalysts with high DRM catalytic performance for methane conversion were synthesized on sedimentary palygorskite?SPal?.Al apparently favored the dispersibility of nickel particles on the surface of SPal,enhancing the catalytic activity and stability of the catalysts.These results should be due to the strong interaction between nickel and the support.The carbon deposition was constantly consumed during the DRM reaction process,showing negligible influence on the catalyst for DRM reaction.?2?Hydrothermal palygorskite?HPal?supported nickel catalysts were also synthesized.Ni₈/Al₈/HPal catalysts showed excellent performance for DRM reaction.The CH₄conversion and CO₂ conversion is 95%and above 90%,respectively.However,the excessive Ni loading?10%?would lead to the sintering of nickel particles and decrease of specific surface area,resulting in the decrease of catalytic performance.?3?The results showed that both lattice-iron and the supported-iron have negative effects on the Ni_x/Pal catalysts for DRM.The Ni₈/SPal and Fe_xNi₈/HPal catalysts showed lower catalytic performance than that of the Ni_x/HPal catalysts.The poor catalytic performance of Ni_x/HPal and Fe_xNi₈/HPal catalysts indicated that the supported-iron and the substituted iron would significantly effect the catalysts for DRM reaction,which can be attributed to the strong interaction between Ni and lattice-iron and between Ni and the supported-iron.Iron atom would gradually migrate to the surface of nickel particles covering the active sites.This phenomenon could reduce the number of active sites on the surface of Pal resulting in the deactivation of the Ni-based catalysts.In addition,the aggregation of nickel particles,and formation of graphite-type carbon deposition were also the main reasons for the deactivation of the Ni-based catalysts.