Sandwiched Si02@Ni@Zr02 as a Coke Resistant Nanocatalyst for Carbon Dioxide Reforming with Addition of Methane

摘要

Design active and coke resistant Ni based catalysts is critical for implementation of dry reforming of methane technology f [1-4]. In this work, coke resistant SiPO_2@Ni@ZrO_2 catalyst has been successfully prepared through precipitation of nickel nitrate with ammonia onto silica spheres, followed by coating with porous ZxO_2 shell. Through thermal treatment in air and hydrogen, nickel nanoparticles with size of 6 nm were uniformly sandwiched between silica core and zirconia shell. The ZrCh coated Nicatalyst exhibited a high activity of-13.0 mol ch4 per gram of Ni per hour for methane dry reforming at 700 °C, which is more than 6 times higher than that of Si02@Ni catalyst under the same reaction condition. The Si02@Ni@ZrC>2 catalyst is also coke resistant as no carbon formation was observed for methane dry reforming at 700 °C for 20 h. As a comparison, carbon nanotubes formed over Si02@Ni catalyst during dry reforming reaction with a coking rate of 0.019 gram of carbon formed per gram of catalyst per hour. Operando XANES/EXAFS study of Si02@Ni@ZrC>2 catalyst confirmed metallic Ni phase during methane dry reforming from 400 to 800 °C. Theoretical calculations suggests that ZrO_2 stabilized Ni clusters lowers the highest dissociation energy barrier of CH4 and CO_2 by 1.37 and 2.56 eV comparing to bulk Ni, increasing dry reforming activity on SiO_2@Ni@Zr02 catalyst. Furthermore, the higher binding energy of CO_2 over CH4 on Si02@Ni@ZrC>2 leads to enrichment of CO_2 on catalyst surface, which mitigates coke formation.