Catalyst Preparation And Reaction Mechanism Of Thermocatalytic Decomposition Of Methane

With the depletion of fossil fuel resources and the increasing environmental pollution caused by it,people must find new energy sources to replace fossil fuels as soon as possible.As a clean secondary energy source,hydrogen is considered to be one of the most promising alternative energy sources and clean fuels.Thermocatalytic decomposition of methane?TCD?to produce hydrogen has attracted much attention because of its simple process and no carbon oxides in the products.Catalyst activity and reaction conditions are the main factors affecting hydrogen production,structure and morphology of carbon products in TCD reaction.Therefore,the preparation of efficient catalysts and the selection of appropriate reaction conditions are of great significance for the application of thermocatalytic decomposition of methane.In this paper,nickel-based catalysts were used to study the effects of different metal additives,metal loading,precursors of catalytic components and different reaction conditions on the performance of catalysts.In addition,the kinetics of thermocatalytic decomposition of methane was also studied.The main research contents and results are divided into the following aspects:1.In this part,the catalysts performance of M-Ni/Al₂O₃ on thermocatalytic decomposition of methane catalyst was studied.5 wt%M-60 wt%Ni/Al₂O₃catalysts with different metal additives?M=Cu,Mn,Pd,Co,Zn,Fe,Mg?were prepared by impregnation method using?-Al₂O₃ as support.Under certain reaction conditions,the change of methane conversion over time and the structure and morphology of carbon products produced by thermocatalytic decomposition of methane were investigated in a fixed-bed reactor.The results showed that the methane conversion of thermocatalytic decomposition of methane on the catalyst increased with the addition of active metal components such as Cu,Mn,Pd,Co,Fe and Mg except Zn.The catalytic activity of 5 wt%Mn-60 wt%Ni/Al₂O₃ was significantly improved by adding Mn.The CH₄ conversion was about 80%.The lifetime of 5 wt%Cu-60 wt%Ni/Al₂O₃ catalyst was prolonged obviously,the conversion of CH₄ decreased from 61%to 45%after 250 minutes.After the reaction,carbon nanofibers were formed on all nickel-based catalysts.The surface of CNFs formed on 5 wt%Mg-60 wt%Ni/Al₂O₃ catalyst was clean.2.In this part,the catalysts performance of Ni-Mn-Ru catalyst on thermocatalytic decomposition of methane was investigated.The effects of Ru metal loading,reaction conditions?reduction temperature,reduction time,reaction temperature and gas space velocity?,RuCl₃·xH₂O?anhydrous?,and Ru?NO??NO₃?_x?OH?_y?x+y=3?on the performance of three-component metal-supported 60 wt%Ni-5 wt%Mn-x%Ru/Al₂O₃ catalysts were investigated.The experimental results show that when Ru?NO??NO₃?_x?OH?_y?x+y=3?precursor is selected,the methane conversion can reach 93.76%with the Ru loading is 10%,the reaction conditions are reduction at 700?C for 1 h and reaction temperature is750?C,the space velocity of 36000 mL·g^-1·h^-1.Carbon nanofibers formed on the catalyst have unique morphological characteristics.Some fibers are coiled into clusters and dispersed in the fibers.3.In this part,the mechanism of thermocatalytic decomposition of methane of studied.The 60 wt%Ni-5 wt%Mn-10 wt%Ru/Al₂O₃ catalyst using Ru?NO??NO3?_x?OH?_y as precursor was used for thermocatalytic decomposition of methane.The kinetics of thermocatalytic decomposition of methane was studied at different temperatures and CH₄ partial pressures.And the intermediate gas products which may be produced in the reaction process were detected by rapid mass spectrometry.The results show that:the initial hydrogen yield increased with the increase of temperature and partial pressure of methane.The reaction order and activation energy of thermocatalytic decomposition of methane for hydrogen production are 2.17 and 20.3 kJ/mol,respectively.The deactivation reaction order,concentration-dependent parameter of methane and activation energy of catalyst deactivation are 3,1.25 and 92.9 kJ/mol,respectively.A small amount of C₂H₂was detected by rapid mass spectrometry,and the pathway of C₂H₂ production was speculated.