(699a) Confined Ni Nanoparticles in Mesoporous Silica Via a Polyethyleneimine-Assisted Route and Their Catalytic Performance for Methane Dry Reforming

The major greenhouse gases of CH₄ and CO₂ were converted into CO and H₂ synthesis gas via dry reforming of methane with the minimization of the carbon coking on the nickel confined mesoporous silica catalyst. To immobilize nickel nanoparticles in the ordered channels of the mesoporous silica, polyethyleneimine (PEI) was used as a stabilizer, reducing, and capping agent of nanoparticles. The nickel-PEI chelated complexes were formed by dissolving PEI and the nickel precursor into an aqueous solution. Then, the positively charged NH₂ terminal groups of the complexes were strongly interacted with the negatively charged surface silanol groups of the mesoporous silica. From this strong interaction, the nickel-PEI chelates were anchored in the porous framework of their parent support during the impregnation steps. A long hydrocarbon chain of PEI and its steric hindrance prevented the aggregation of the nickel-PEI complexes during the drying and calcination steps. Therefore, nickel nanoparticles were highly dispersed inside the porous framework even after the reduction step, suggesting the successful synthesis of the nickel well-dispersed mesoporous silica catalyst via a PEI-assisted route. Whereas the carbon coking was severely generated on the catalyst without PEI (177 g_carbon/g_cat for 40hr), the PEI-assisted catalyst showed the superior catalytic stability for dry reforming of methane with the minimization of the carbon coking (3.63 g_carbon/g_cat for 40hr). The synthesized nickel nanoparticles without PEI were placed outside of the porous structure and then, easily aggregated more than their parent support with the severe carbon coking. On the other hands, the sintering of nickel nanoparticles was more effectively hindered and the generation of carbon coking was suppressed on the confined nickel nanoparticles, since the prepared nickel particles via a PEI-assisted route were well-confined inside the pore. Therefore, combined with the simple procedure and low cost, the PEI-assisted route is one of the most promising methods for embedding nickel nanoparticles in mesoporous framework.