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

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 La(1-x)A(x)NiO(3)/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. H-2-TPD results demonstrated that Sr2+ and Ba2+ cations significantly enhanced the dispersion of Ni-0 active sites within the catalyst compared to LaNiO3/DMSN, contrasting with the effects of Ca2+. Further investigation through H-2-TPR revealed a more complex reduction process in the Sr2+ and Ba2+-doped samples compared to the bare catalyst. Analysis of O-2-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 degrees 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 Ni-0 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.