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

Abstract

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, H2 chemisorption, N2 physisorption, transmission electron microscopy, and temperature-programmed reduction. Reduction of the calcined hydrotalcite converted the (Al:Ca:Mg:Ni)Ox mixed oxide into nickel and CaO particles supported on an (Al:Mg)Ox matrix with a surface area of 54 m2·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)Ox 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 H2 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.