Sandwiched SiO2@Ni@ZrO2 as a coke resistant nanocatalyst for dry reforming of methane

Abstract

Design active and coke resistant Ni based catalysts is critical for implementation of dry reforming of methane technology. In this work, coke resistant SiO2@Ni@ZrO2 catalyst has been successfully prepared through precipitation of nickel nitrate with ammonia onto silica spheres, followed by coating with porous ZrO2 shell. Through thermal treatment in air and hydrogen, nickel nanoparticles with size of 6 nm were sandwiched between silica core and zirconia shell. The ZrO2 coated Ni catalyst 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 SiO2@Ni catalyst under the same reaction condition. The SiO2@Ni@ZrO2 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 SiO2@Ni catalyst during dry reforming reaction with a coking rate of 0.019 g of carbon formed per gram of catalyst per hour. Operando XANES/EXAFS study of SiO2@Ni@ZrO2 catalyst confirmed metallic Ni phase during methane dry reforming from 400 to 800 °C. Theoretical calculations suggests that ZrO2 stabilized Ni clusters lowers the highest dissociation energy barrier of CH4 and CO2 by 1.37 and 2.56 eV comparing to bulk Ni, increasing dry reforming activity on SiO2@Ni@ZrO2 catalyst. Furthermore, the higher binding energy of CO2 over CH4 on SiO2@Ni@ZrO2 leads to enrichment of CO2 on catalyst surface, which mitigates coke formation.