Study On The Preparation Of Ni-MCM-41 Catalysts And Performance For Partial Oxidation Of Methane

As the associated mineral resources of coal,coalbed methane is very rich in reserves and ranks third in the world.However,in the process of mining,low-concentration coalbed methane is directly vented due to low utilization rate,causing serious waste of resources.Partial oxidation of methane（POM）as one of the effective ways to use low-concentration CBM has been the focus of many scholars.The POM reaction is a slight exothermic reaction,which greatly reduces the energy requirement during the reaction.The appropriate H₂/CO ratio is suitable for the synthesis of methanol and other downstream products.To date,Ni-based catalysts have been extensively investigated for POM reactions due to their excellent catalytic performance,wide availability,and low cost.However,Ni-based catalysts are prone to carbon deposition and sintering,which in turn leads to deactivation of the catalyst.In order to solve the above problems and improve the catalytic performance and long-term stability of the catalysts,mesoporous Ni-MCM-41 catalysts,Co-Ni-MCM-41 catalysts,Ni-MCM-41catalysts with different pore sizes were prepared and used in this paper.In the POM reaction,the physicochemical properties of the catalyst were characterized and characterized by XRD,TEM,FT-IR,BET,ICP,H₂-TPR,and TGA.The catalyst preparation method,active component content,average pore size,and metal particle size were investigated.The influence of metal dispersibility,reaction temperature and airspeed on the structure and catalytic performance of the catalyst.The main contents are as follows:1.Mesoporous Ni-MCM-41 catalyst was prepared by in-situ synthesis method using CTAB as template and compared with Ni/MCM-41 catalyst prepared by traditional impregnation method.The experimental results showed that:（1）In-situ synthesis method was used.The prepared catalyst successfully introduced the metal Ni into the inside of the molecular sieve,and the obtained catalyst metal particle size was small and the dispersion degree was high.With the increase of the introduced Ni content,the long-range ordering of the molecular sieve was destroyed when the content of the introduced Ni reached15%.Mesoporous structure is preserved.However,the Ni/MCM-41 catalyst metal prepared by traditional impregnation method is supported on the catalyst surface in the form of NiO,which not only reduces the specific surface area of the catalyst,but also causes the metal to easily migrate and agglomerate at high temperatures.（2）There are two forms of metal entering the molecular sieve,one enters the middle of the molecular sieve channel,and the pores of the molecular sieve can control the growth of the metal nanoparticles,and the other is connected with the framework of the molecular sieve to improve the interaction between the metal and the carrier.Force,thereby increasing the catalyst reduction temperature.（3）10%Ni-MCM-41 catalyst showed excellent performance in the catalytic performance test of POM reaction,the conversion rate of CH₄ was 87%,the selectivity of H₂ was 82%,and the catalytic activity gradually increased with the increase of temperature,and There is no decline in the stability over a long period of time,which is due to the high specific surface area of the 10%Ni-MCM-41 catalyst,the smaller size of the metallic Ni nanoparticles,and the high degree of dispersion.2.In the process of preparation of mesoporous Ni-MCM-41 catalyst,Co was added to prepare Co-Ni-MCM-41 catalyst and compared with Ni-MCM-41catalyst.The experimental results show that:（1）using in situ The synthesis method successfully introduces Co ions and Ni ions into the interior of the molecular sieve,and the obtained catalyst has smaller particle size and higher dispersity than the Ni-MCM-41 catalyst,but when the content of Co reaches1.5%,the molecular sieve is The skeleton structure was partially destroyed,resulting in a significant decrease in the specific surface area.（2）The results of ICP and H₂-TPR analysis show that the introduction of Co ions facilitates the formation of NiCo alloy with Ni into the molecular sieve pores.When the content of Co was 0.5%and 1%,a large amount of metallic Ni was found in the catalyst after the reaction,which proved that the introduction of Co ions increased the lanthanum sintering performance of the catalyst.（3）The catalytic activities of 0.5%Co-Ni-MCM-41 and 1%Co-Ni-MCM-41 catalysts are higher than those of Ni-MCM-41 catalysts,and the catalysts are catalyzed by1%Co-Ni-MCM-41 catalyst.With the highest activity,CH₄ conversion and CO selectivity were both 92%.The catalyst maintained high activity for a long time,and the catalytic activity decreased with the increase of reaction space velocity.3.In the process of preparation of mesoporous Ni-MCM-41 catalyst,the expansion agent TMB was added to prepare Ni-MCM-41 catalysts with different pore sizes.The comparison with Ni-MCM-41 catalyst showed that:（1）TMB Addition can increase the pore size of MCM-41 continuously,but excessive TMB will destroy the framework structure of molecular sieve.When TMB/CTAB=4,the catalyst skeleton structure collapses,causing the agglomeration of metal particles to become larger,and when TMB/CTAB at the3,the metal particles in the catalyst are uniformly dispersed and the particles are smaller,which means that the increase of the pore size of the catalyst helps to reduce the size of the metal particles and improve the dispersibility of the metal.（2）As the pore size of the catalyst becomes larger,the metallic Ni nanoparticles originally confined in the middle of the molecular sieve pores become free,most of them are washed away during filtration,and a large amount of metal Ni is connected to the skeleton,which enhances the interaction between the metal and the carrier.Increase the reduction temperature of the catalyst.（3）When TMB/CTAB=3,the catalyst（3TA）exhibits excellent catalytic activity,the conversion rate of CH₄ reaches 95%,and the CO selectivity reaches 90%,indicating that the larger average pore diameter is not conducive to the formation of carbon deposits.Effectively improve the catalytic performance of the catalyst.