Sorption-enhanced steam reforming of toluene using multifunctional perovskite phase transition sorbents in a chemical looping scheme

Abstract

Sorption-enhanced steam reforming (SESR) of toluene (SESRT) using catalytic CO _2 sorbents is a promising route to convert the aromatic tar byproducts formed in lignocellulosic biomass gasification into hydrogen (H _2 ) or H _2 -rich syngas. Commonly used sorbents such as CaO are effective in capturing CO _2 initially but are prone to lose their sorption capacity over repeated cycles due to sintering at high temperatures. Herein, we present a demonstration of SESRT using A- and B-site doped Sr _1− _x A’ _x Fe _1− _y B’ _y O _3− _δ (A’ = Ba, Ca; B’ = Co) perovskites in a chemical looping scheme. We found that surface impregnation of 5–10 mol% Ni on the perovskite was effective in improving toluene conversion. However, upon cycling, the impregnated Ni tends to migrate into the bulk and lose activity. This prompted the adoption of a dual bed configuration using a pre-bed of NiO/ γ –Al _2 O _3 catalyst upstream of the sorbent. A comparison is made between isothermal operation and a more traditional temperature-swing mode, where for the latter, an average sorption capacity of ∼38% was witnessed over five SESR cycles with H _2 -rich product syngas evidenced by a ratio of H _2 : CO _x > 4.0. XRD analysis of fresh and cycled samples of Sr _0.25 Ba _0.75 Fe _0.375 Co _0.625 O _3- _δ reveal that this material is an effective phase transition sorbent—capable of cyclically capturing and releasing CO _2 without irreversible phase changes occurring.

Keywords

• syngas
• perovskite oxide
• sorption-enhanced steam reforming
• chemical looping
• phase transition sorbents