Design of stable Ni/ZrO2 catalysts for dry reforming of methane

ZrO2 supported Ni with an average particle diameter of 1–2 nm were synthesized by binding Ni2+ in rccc-5,11,17,23-tetrahydroxy-2,8,14,20-tetra(n-decyl)resorcin[4]arene (pyrogallol[4]arene) nanocapsules as Ni precursor. The Ni/ZrO2 catalyst with a 1.1 nm particle diameter showed outstanding stability in dry reforming of methane (DRM), which maintained nearly 90% of the initial activity after 60 h time on stream. The high stability is attributed to nearly all Ni atoms being located at the interface and perimeter to ZrO2. This led to a higher accessibility to the oxygen from activated CO2 at the Ni-ZrO2 interface, facilitating conversion of surface carbon to CO. Ni/ZrO2 catalysts with larger Ni particle diameter have a fraction of non-perimeter Ni that deactivates rapidly. The decrease of the H2 formation rate was faster with time on stream than the decrease of the H2O formation rate. At longer time on stream the ratio of H2O to H2 yield reached 0.40 ± 0.08 for all Ni/ZrO2 catalysts, independently if a catalyst was stable from the reaction start or deactivated to a stable level. The ratio between H2O and H2 yield reflects the abundance of oxygen availability on the Ni surface, the oxygen availability index (OAI). For an OAI value of 0.40, the deactivation of Ni catalyst was negligible, while below that deactivation was pronounced. The reorganization of surface carbon to graphitic overlayers and carbon fibers is hypothesized to start from surface domains that are not adjacent to the metal-support perimeter.