Production of hydrogen-rich syngas using Zr modified Ca-Co bifunctional catalyst-sorbent in chemical looping steam methane reforming

Abstract

High purity H2 could be produced through modified chemical looping steam methane reforming (CL-SMR) process using calcium asan essential component in the structure of bifunctional catalyst-sorbents. Herein, we present an effective approach to the production of high purity hydrogen in chemical looping reforming of methane via modification of a bifunctional Ca-Co-Zr catalyst-sorbent. The synthesis of the samples including pure Ca, Ca-Co and zirconium modified Ca-Co with different molar ratios was performed using co-precipitation method. The influence of reaction variables such as steam to carbon molar ratio (S/C=1–5), reaction temperature (500–750°C) and lifetime of the samples are investigated on methane conversion and hydrogen yield. Moreover, Ca/Co mass ratio (0.11–9) is optimized and subsequently, different amounts of zirconium promoter (mass ratio=2.25–18) are added to improve the bifunctional catalyst-sorbent structure. The characterization of samples was performed using XRD, FESEM, BET and EDX techniques. It is found that the addition of zirconium to the sample could improve the textural features and stability of bifunctional catalyst-sorbent. The results reveal that Ca-Co-Zr (via mass ratios of CaCo=9 and CaZr=4.5) exhibits the highest catalytic activity among all tested samples and shows 98.3% methane conversion and 84.5% hydrogen yield at 700°C. The cyclic life time results at 700°C indicated that the Ca-Co-Zr (9,4.5) bifunctional catalyst-sorbent remained stable up to 16 cycles, while non-promoted samples showed fast deactivation after about 10 redox cycles. The coke formation is inhibited, while the reaction pathway changes to a combined reaction. In summary, the obtained results show the suitable efficiency of the synthesized catalyst in the modified CL-SMR process.