Study On ZSM-5 Supported Metal Catalysts For Partial Oxidation Of Methane

Coalbed methane is an unconventional gas associated with coal.Coalbed methane is the main source of serious accidents in coal mines,and the extraction and emptying of coalbed methane will cause serious damage to the atmospheric environment and cause greenhouse effect.Partial oxidation of methane to synthesis gas(POM)has the advantages of relatively low energy consumption and mild reaction conditions,and its suitable H₂/CO is conducive to methanol production and F-T synthesis.The active metals of the reaction can be divided into transition metals(Ni,Co,etc.)and precious metals(Rh,Ru,Ir,Pt,Pd,etc.).The preparation cost of noble metal catalyst is high.In view of the above problems,this paper prepared Ni@ZSM-5 and Pt@ZSM-5 metal encapsulation catalysts,applied them to the study of POM reactivity,and characterized their physicochemical properties by means of TEM,CO-DRIFTS and FT-IR.The effect of the size of metal particles and the form of Pt in molecular sieve on the reaction performance was investigated.The main research contents are as follows:1.Using N-(2-aminoethyl)-3-aminopropyl trimethoxysilane(TPE)as the ligand,the Ni@ZSM-5 and Ni-Pt@ZSM-5 catalyst was synthesized in situ under hydrothermal conditions to inhibit metal sintering and carbon deposition through pore limiting action of zeolite.The results showed that the catalysts with different sizes and yields were compared in the hydrothermal crystallization process.(1)ZSM-5 zeolite particles were relatively large(1?m)after crystallization at 170 ? for 72hours.(2)ZSM-5 zeolite particles were small(100?200nm)after 72 hours of crystallization at 120 ?,but the yield was low(58%).(3)the size(100-200nm)and yield(>90%)of the molecular sieve were effectively controlled by two-stage crystallization(48 h at 100? and 24 h at 170?).Compared with Ni/ZSM-5 prepared by traditional impregnation method,the Ni@ZSM-5 catalyst has higher activity and anti-carbon deposition and anti-sintering ability.The metal Ni is more evenly dispersed in the molecular sieve.The restriction effect of the molecular sieve makes the metal particles have more active sites.For Ni@Pt-ZSM-5 catalyst mixed with a small amount of Pt,oxygen treatment did not bring better POM activity,and nickel oxide particles formed after oxygen treatment were not conducive to POM reaction.2.The catalysts Pt@S-1,Pt@ZSM-5 were successfully synthesized under hydrothermal conditions.The experimental results showed that after hydrogen and oxygen pretreatment,the Pt@S-1 catalyst showed stable conversion and selectivity under the condition of 40 hours of high temperature reaction,and the catalyst after hydrogen treatment had slightly higher catalytic performance.However,for Pt-ZSM-5,the selectivity of the product after oxygen pretreatment was much higher than that of the catalyst after hydrogen pretreatment.The dispersion of Pt in Pt@ZSM-5 was observed by TEM characterization after high temperature oxygen pretreatment.By changing the oxygen treatment temperature,it was found that Pt particles had the best dispersion when the treatment temperature was between 350 ? and 550 ?.Atomically dispersed Pt particles could be observed by spherical differential electron microscopy.The Pt-ZSM-5 catalyst treated in oxygen had better POM activity than the Pt-ZSM-5 catalyst treated in hydrogen,because the Pt particles were smaller after the oxygen treatment and there were more active sites in the catalyst.