Study On The Preparation Of Highly Dispersed Pt Catalysts And Performance For Partial Oxidation Of Methane

Coalbed methane is an unconventional natural gas that is stored in the coal seam in an adsorbed state.In the process of coal mining,low-concentration coalbed methane is generally discharged directly into the air,which will result in waste of resources and greenhouse effect,and encounters an open flame,which is prone to gas explosion.This thesis studies how to effectively utilize low-concentration coalbed methane,and methane partial oxidation?POM?is one of the ways to use it.Because the POM reaction is a mild exothermic reaction,the equipment is simple,and the H₂/CO ratio in the product is favorable for the formation of alkanes and alcohols in downstream products.In view of the current problem of easy carbon deposition and sintering of the catalyst,this paper selects the precious metal Pt with the advantage of anti-carbon deposition,and encapsulates it in the zeolite to improve its anti-sintering ability.And the catalyst is heat-treated under low temperature oxygen conditions to reduce the particle size to improve the dispersibility of Pt,improve the effective utilization of Pt,and thereby reduce the cost.In this paper,the catalyst of Pt@S-1,Pt@Ni-MCM-41,Pt@Co-MCM-41 were prepared and applied to the partial oxidation of methane.The catalyst was analyzed by XRD,BET,FT-IR,UV-Vis,H₂-TPR,TEM and TG-DTG.The effects of oxygen treatment,different reaction temperatures,different preparation methods and different active components on the POM were investigated.The conclusion is as follows:1.Highly dispersed Pt nanoparticles confined within S-1 zeolite was synthesized via the hydrothermal synthesis.Compared with conventional Pt/S-1catalyst prepared by incipient-wetness impregnation method,the Pt@S-1catalyst has has more favorable for the catalytic performance of methane partial oxidation.Because Pt nanoparticles of catalyst are small in size and uniformly dispersed in the pores by the hydrothermal synthesis.However,Pt particles by the conventional method are not uniformly dispersed,and some are on the surface of the zeolite,blocking the pores,and reducing the contact between the active sites and the reactants.When the loading of Pt is 0.4%and the reaction temperature is 800?,the catalyst has the best catalytic effect,wherein CH₄conversion is 80%,H₂ selectivity is 100%,and CO selectivity is 80%.2.Oxygen heat treatment of Pt@S-1 and Pt/S-1 catalysts is carried out can further improve the dispersibility of the catalyst Pt and improve the utilization rate before the POM reaction.It can be seen from the TEM image that the300? oxygen heat treatment can reduce the size of Pt nanoparticles,improve its dispersibility,and improve the catalytic performance.3.Introducing another active component?nickel or cobalt?into the Pt@MCM-41 catalyst is synthesized by hydrothermal synthesis-coprecipitation method.Nickel or cobalt is doped on the skeleton in a tetracoordinate form to prevent sintering during the preparation of the catalyst and to improve the dispersibility.It was found that the doping amount of Ni was 2%and the doping amount of Co was 5%,and the catalytic effect was optimal.The characterization indicates that the addition of Ni and Co is beneficial to increase the density of hydroxyl groups during the reaction.The more the density of hydroxyl groups,the more favorable the POM reaction.It can be clearly concluded that the doping of Ni and Co improve the catalytic performance,but Ni has a better effect than Co and is more favorable for the POM reaction.