Investigation of Cu promotion effect on hydrotalcite-based nickel catalyst for CO₂ methanation

The present research focuses on a Ni-Mg-Al hydrotalcite-derived catalyst promoted with Cu. Catalysts were prepared by the co-precipitation method at constant pH and were subsequently characterized via XRD, H-2-TPR, CO2-TPD, TGA, XAS, TEM, low-temperature nitrogen sorption and tested for CO2 hydrogenation to methane. The methanation reaction was carried out at GHSV of 12,000 ml.g(-1) h(-1) and high selectivity (above 98%) and activity in CO2 conversion (up to 86%) were observed at 350 degrees C on the HTNi15Cu1 sample containing 1.3 wt% Cu. The influence of Cu promotion was especially visible at low temperatures (250-300 degrees C) where significant CO2 conversion is observed when compared to the non-promoted sample. The sample with the highest copper content was less selective for methane formation but promoted the reverse water-gas shift reaction. Also, its activity was the worst in the examined series, indicating that high Cu concentrations are not suited for CO2 methanation. It was likewise observed that with an increase in Cu content, Ni-Cu solid solution is formed. Later, during the methanation reaction, Ni-Cu alloy undergoes redispersion due to the atomic erosion effect, forming well dispersed nickel nano-crystallites.