Sorbent-Enhanced Methane Reforming over a Ni–Ca-Based, Bifunctional Catalyst Sorbent

A bifunctional catalyst for the sorbent-enhanced steam methane reforming (SE-SMR) reaction was derived from a hydrotalcite-based precursor synthesized via a coprecipitation technique. The material contained both the Ni reforming catalyst and the Ca-based CO 2 sorbent and was characterized using X-ray diffraction, H 2 chemisorption, N 2 physisorption, transmission electron microscopy, and temperature-programmed reduction. Reduction of the calcined hydrotalcite converted the (Al:Ca:Mg:Ni)O x mixed oxide into nickel and CaO particles supported on an (Al:Mg)O x matrix with a surface area of 54 m 2 ·g –1 . The high CO 2 absorption capacity and its stability with carbonation cycles was attributed to the high dispersion of CaO on the porous and thermally stable (Al:Mg)O x network, whereas for naturally occurring limestone, a rapid decay in the CO 2 absorption capacity was observed. Under SE-SMR conditions, the recorded mole fraction of hydrogen in the effluent stream was 99 vol % (dry and without inert component); that is, thermodynamic equilibrium calculated to be 99 vol % (without inert component) was reached. The CO 2 uptake of the bifunctional material averaged 0.074 g CO 2 /g sorbent over 10 cycles. After approximately seven cycles, the CO 2 capture capacity stabilized, resulting in an average decay rate of only 0.3% per cycle over the last three cycles. The bifunctional material developed here produced a larger amount of high-purity H 2 than limestone mixed with Ni–SiO 2 or a Ca-free, nickel hydrotalcite-derived catalyst, making the new material an interesting candidate for the SE-SMR process.