Sorption enhanced steam reforming of methane over waste-derived CaO promoted MgNiAl hydrotalcite catalyst for sustainable H2production

Abstract

The waste-derived CaO promoted Mg-Ni-Al (MNA) based hydrotalcite hybrid catalysts were synthesized by co-precipitation and wet impregnation method and tested for sorption enhanced steam methane reforming (SESMR) for hydrogen (H2) production. The catalysts were characterized using X-ray diffractometer (XRD), Field emission scanning electron miscroscopy (FESEM), Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, Brauner Emmett teller (BET), laser particle size analyzer, Temperature programmed reduction (TPR), Thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). Various CaO loadings varying from 0% to 15% into the MNA-based hydrotalcite catalysts (MNA HTc) were assessed for SESMR in a fixed bed reactor. The results revealed that 10% CaO@MNA exhibited the best performance in terms of a longer pre-breakthrough period with respect to other compositions. The CH4 fraction, H2 purity, and CO2 production in the absence of CaO were marked at 60%, 55%, and 14% respectively. However, the CH4 fraction and H2 purity increased to 77% and 80%, while CO2 decreased to 3% in the pre-breakthrough period for 10% CaO @ MNA at 650 °C, WHSV 2000 mL CH4 g-1h-1 and S/C of 2.0. The nanocomposite 10%CaO@MNA was tested over three consecutive SESMR cycles at 650 °C to analyze its regeneration capacity. The hybrid catalyst was also tested at various temperatures from 650° to 850°C to investigate the effect of CaO sorbent. It was found that elevated temperatures > 750 °C likely reduced the carbonation reaction and shifted the technique to SMR. The spent catalyst exhibited negligible carbon formation on the catalyst surface. The catalytic performance of the reported catalyst-sorbent system is encouraging for further regeneration studies for SMR and other reforming techniques.