Probing CO2 methanation enhancement on dendritic mesoporous silica nanoparticle supported alkaline-earth ion doped LaNiO3-derived catalysts: The dominant role of Ni0 active sites over oxygen vacancies

Abstract

To thoroughly explore the role of alkaline-earth ions in enhancing the CO2 methanation performance of LaNiO3/dendritic mesoporous silica nanoparticle (DMSN) catalysts, a series of La1-xAxNiO3/DMSN (x = 0, 0.1; A = Ca, Sr, Ba) catalysts was synthesized. XRD analysis revealed the predominant integration of Sr2+ species into the LaNiO3 crystal lattice, while the Ca2+ and Ba2+-doped samples formed additional crystalline phases of CaO and BaO2, respectively. H2-TPD results demonstrated that Sr2+ and Ba2+ cations significantly enhanced the dispersion of Ni0 active sites within the catalyst compared to LaNiO3/DMSN, contrasting with the effects of Ca2+. Further investigation through H2-TPR revealed a more complex reduction process in the Sr2+ and Ba2+-doped samples compared to the bare catalyst. Analysis of O2-TPD and CO2-TPD data showed a direct relationship between surface oxygen vacancies and moderate alkaline sites, with a more pronounced presence in the Ba2+ and Sr2+-doped samples. The overall activity below 450 °C followed the sequence of La0.9Sr0.1NiO3/DMSN > La0.9Ba0.1NiO3/DMSN > LaNiO3/DMSN > La0.9Ca0.1NiO3/DMSN. From the stability perspective, the La0.9Ba0.1NiO3/DMSN catalyst exhibited lower carbon/coke deposition than its Sr2+-promoted counterpart in TGA and Raman analyses. These findings highlighted that the dispersion of Ni0 species and oxygen vacancies emerged as the primary determinants of catalytic activity and stability, respectively. This indicated that while La0.9Sr0.1NiO3/DMSN achieved higher CO2 conversion and CH4 selectivity compared to La0.9Ba0.1NiO3/DMSN, it also experienced more carbon/coke deposits, leading to a shorter catalytic lifespan.