Partial Oxidation Of Methane Into Syngas Catalyzed By Metallic Nickel-Based Monolithic Catalysts

Methane partial oxidation to syngas is one of the promising ways to efficiently utilize methane. Because of its low investment and energy consumption with instant reaction rate, it has attracted much attention. In the present work, Ni metallic monolith catalyst was prepared with Ni foam and further treated by acid. It was loaded by promoter oxides, such as ceria, zirconia, magnesia, ceria-zirconia, etc., to obtain the Ni monolith with oxides. The sample characterization was made by XRD,XPS,SEM,ICP and BET. Considering that the deactivation of the Ni metallic monolith could not occur and it had lower activity than the supported catalysts, the dual bed, Ni monolith-Ni/MgAl2O4, was also studied for methane partial oxidation. Moreover, on the basis of an indirect reaction mechanism, simulations of methane partial oxidation were conducted for these three kinds of catalyst systems.SEM micrographs showed that the crystal defects on the surface of the Ni monolith were formed. The surface area increased from 0.3m2/g of untreated Ni monolith to 0.5m2/g of the Ni monolith treated by acid. At inlet temperature 1123 K, CH4/O2 ratio of 2 and GHSV 1.0×105 h-1, methane conversion and selectivities to H2 and CO on the Ni monolith treated by acid were 90%, 98% and 95%, respectively, much higher than those of the untreated Ni monolith, which were 84%, 92% and 94%, respectively.The optimal loadings of ceria and zirconia, separately, were 2.87% and 1.57%, respectively. The optimal loading of magnesia was 4.03% while calcium oxide had no role for promotion of the activity and the selectivities. 0.87%Ce-1.77%Zr/Ni showed not only high activity and selectivities, but also high stability. XRD patterns showed that CeO2-ZrO2 solid solution was formed on 0.87%Ce-1.77%Zr/Ni.The results showed that the reaction performance for the combined partial oxidation and steam reforming of methane was better than the combined partial oxidation and carbon dioxide reforming of methane on both Ce-Zr/Ni monolith and Mg/Ni.The dual bed, Ni monolith-Ni/MgAl2O4, had the highest activity and selectivities when the nickel loading on the reforming catalyst was 10wt. %. The results showed that when the feed flowrates were 500 ml/min or 1000 ml/min, 2.3 or 4.7 mm of the minimum length of the Ni monolith were needed, respectively, to achieve nearly constant methane conversion and the selectivities to hydrogen and carbon monoxide and the maximum temperatures were within the Ni monolith bed. In order to obtain high methane conversion and high selectivities to syngas, the minimum length of the Ni/MgAl2O4 bed length was 2.4 mm at 500 mol/min or 3.7 mm at 1000 ml/min, respectively.On the basis of an indirect reaction mechanism, the simulations for the partial oxidation of methane on the Ni metallic monolith catalysts were conducted. The results showed that the simulations agreed well with the experimental data on the Ni monolith bed, and it was likely that the methane partial oxidation followed an indirect reaction mechanism. The simulation results for Ce-Zr/Ni monolith showed that the reaction performance of Ce-Zr/Ni was promoted due to high redox of CeO2-ZrO2 solid solution. The simulation results for Ni monolith-Ni/MgAl2O4 showed that the oxidation bed and the reforming one in the dual bed had an optimal bed length, respectively, which made the dual bed have not only high activity and selectivities but also high stability under the certain flowrates.