3-based perovskite with in-situ exsolved Ni nanoparticles: a highly active, performance stable and coking resistant catalyst for CO 2 dry reforming of CH 4]]>

摘要

Wet impregnation method has been widely adopted to synthesize the oxide substrate supported catalysts for CO2dry reforming of CH4. However, their particle size and distribution are not stable and uniform, causing rapid particle growth and carbon deposition. Here, we show that these problems can be overcome by using a LaMnO3(LM)-based perovskite in which 20?mol% Ni is doped (La0.9Mn0.8Ni0.2O3, LMN) and then exsolved (R-LMN) by in-situ reduction in 5%H2-N2stream at 800?°C. The perfomance of such catalyst is compared with that of the Ni-impregnated LM (NLM) reduced under the same conditions (R-NLM). The SEM and TEM analyses reveal that the exsolved Ni nanoparticles in R-LMN are uniform in size, evenly distributed and partially embedded into and hence bonded strongly with the substrate; but the Ni particles in R-NLM are variable in size and weakly bonded with the substrate. Therefore, the particle growth (coalescence) is largely suppressed for the exsolved Ni nanoparticles in R-LMN but not for the Ni nanoparticles in R-NLM. It is also comfirmed that the Ni particles in R-NLM are lifted off from the substrate by carbon fibers formed during test. Consequently, R-LMN demonstrates high and stable conversion (above 80%) and selectivity (above 90%) with a strong resistance to carbon deposition at 700?°C for 24?h. But, a large amount of carbon fiber is formed with a Ni particle at the tip in tested R-NLM, resulting in rapid performance degradation. The high performance of R-LMN for CO2dry reforming of CH4is attributed to the stable nanosized Ni particles and LMN substrate that provides more oxygen vacancies for CO2activation and in turn carbon oxidation.