Sol-gel-derived, CaZrO3-stabilized Ni/CaO-CaZrO3 bifunctional catalyst for sorption-enhanced steam methane reforming

Abstract

Sorption-enhanced steam methane reforming (SESMR) that combines steam reforming of methane with in situ CO2 removal is a promising technology for H2 production, and bifunctional catalysts that integrate catalytic and absorptive sites into one body are believed to have reduced mass transfer resistances. However, it is still a challenge to prepare bifunctional catalysts with high stability. Here, we used a sol-gel technique based on the formation of citrate complexes to prepare a series of Ni/CaO-CaZrO3 bifunctional catalysts in which Ni, CaO and CaZrO3 acted as catalyst, sorbent and stabilizer, respectively. The stabilizer, Ni loading and CaO content had a direct effect on the structure and morphology of the catalyst, which in turn influenced its CO2 uptake and SESMR performance. Compared to Ni/CaO, the CaZrO3-stabilized Ni/CaO-CaZrO3 had smaller and fluffier grains, showing not only higher CO2 uptake and better stability in 50 carbonation-calcination cycles, but also higher stability during cyclic SESMR process. In particular, the catalyst with a Ni loading of 15wt%, CaO content of around 60wt% and CaZrO3 content of 25wt% presented the best SESMR performance by taking into account the catalytic activity and stability as well as the duration of the prebreakthrough period. However, the best catalyst was still subject to slow deactivation during a long-term stability test (up to 90 SESMR cycles), which was mostly due to the smooth and compact shell formed on the catalyst surface. The partially deactivated catalyst can be effectively reactivated by an additional carbonation step during the cyclic SESMR operation.