Impact of Sr Addition on Zirconia-Alumina-Supported Ni Catalyst for CO x -Free CH 4 Production via CO 2 Methanation.

Zirconia-alumina-supported Ni (5Ni/10ZrO 2 +Al 2 O 3 ) and Sr-promoted 5Ni/10ZrO 2 +Al 2 O 3 are prepared, tested for carbon dioxide (CO 2 ) methanation at 400 °C, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, surface area and porosity, infrared spectroscopy, and temperature-programmed reduction/desorption techniques. The CO 2 methanation is found to depend on the dispersion of Nickel (Ni) sites as well as the extent of stabilization of CO 2 -interacted species. The Ni active sites are mainly derived from the reduction of 'moderately interacted NiO species'. The dispersion of Ni over 1 wt % Sr-promoted 5Ni/10ZrO 2 +Al 2 O 3 is 1.38 times that of the unpromoted catalyst, and it attains 72.5% CO 2 conversion (against 65% over the unpromoted catalyst). However, increasing strontium (Sr) loading to 2 wt % does not affect the Ni dispersion much, but the concentration of strong basic sites is increased, which achieves 80.6% CO 2 conversion. The 5Ni4Sr/10ZrO 2 +Al 2 O 3 catalyst has the highest density of strong basic sites and the highest concentration of active sites with maximum Ni dispersion. This catalyst displays exceptional performance and achieves approximately 80% CO 2 conversion and 70% methane (CH 4 ) yield for up to 25 h on steam. The unique acidic-basic profiles composed of strong basic and moderate acid sites facilitate the sequential hydrogenation of formate species in the CO x -free CH 4 route.