(406g) Core-Shell Ni-Phyllosilicate@CeO2 Catalyst with Excellent Coke-Resistance in Steam Reforming of Biomass Tar

In this work, a highly active and coke-resistant core-shell structured Ni-SiO₂@CeO₂ catalyst has been developed for steam reforming of biomass tar. A major challenge in the production of hydrogen from biomass gasification is the removal of tar that is formed as a byproduct. Nickel-based catalysts have been shown to be highly active in catalytic steam reforming of tar, but suffer from a high tendency for forming coke that results in blockage of reactors and deactivation of catalyst. Here, we have explored novel core-shell structured catalysts with a Ni-phyllosilicate derived active core and a Cerium oxide shell, that shows high activity (> 60% conversion at 700^oC) and stable performance in steam reforming of toluene as a model tar component. In a 20 hr catalytic test run, the Ni-SiO₂@CeO₂ catalyst showed negligible deposition of coke (ca 0.005 gC/ g-cat hr), whereas a reference Ni-SiO₂ catalyst without the CeO₂ shell showed extensive formation of filamentous carbon (ca 0.08 gC/g-cat hr) under the same reaction conditions, that resulted in blockage of the reactor. The excellent thermal stability and resistance to carbon formation of the Ni-SiO2@CeO2 catalyst is attributed to the high oxygen storage capacity and redox nature of CeO₂, and the confinement effect provided by the CeO₂ shell on the metallic nickel nanoparticles. The ceria shell hinders the spatial movement and sintering of Ni nanoparticle at the high reaction temperature, and thus reduces the tendency of carbon formation, which has been shown to be highly dependent on the Ni particle size. At the same time, the CeO₂ shell can also catalyze the oxidation of the coke precursors deposited on the nickel surface by supplying necessary oxygen species. Different synthesis routes have been explored and synthesis conditions have been optimized to tune the morphology of the core-shell catalyst and maximize the activity by increasing Ni dispersion and minimizing diffusion resistance through the shell. Characterization of catalyst has been done by TEM, XRD, XPS, TPR, and TGA analysis. The influence of reaction temperature on the catalyst performance has also been investigated. Due to its high activity and carbon resistance, the application of this catalyst can be extended to other significant H₂ producing reactions such as dry reforming of methane, steam reforming of ethanol etc.