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 CO2 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 CO2 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 CO2 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 CO2 uptake of the bifunctional material averaged 0.074 g CO2/g sorbent over 10 cycles. After approximately seven cycles, the CO2 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, than limestone mixed with Ni-SiO2 or a Ca-free, nickel hydrotalcite-derived catalyst, making the new material an interesting candidate for the SE-SMR process.