Why the one-pot synthesized Sm-modified nickel phyllosilicate is more active than the post synthesized one for CO2 methanation? Identifying the pivotal role of generating Sm2Si2O7

This work reported an efficient one-pot hydrothermal method for adding promoter to nickel phyllosilicate. The nickel-samarium bimetallic phyllosilicate (NiSm-Ps) was formed during the one-pot synthesis. The character-ization results showed that the Sm species over the uncalcined NiSm-Ps catalyst existed in the form of Sm2Si2O7, and it was converted to be Sm2O3 after calcination with high dispersion, and in the form of Sm2Ox after reduction. On the contrary, for the post-impregnated Sm-doped nickel phyllosilicate catalyst (Ni-Ps/Sm-Im), the Sm species variation was from Sm2O3 to Sm2Ox, which was significantly different from that of NiSm-Ps. As a result, the NiSm-Ps catalyst showed a high Ni dispersion (13.9%), small particle size (4.0 nm) and large con-centration of surface oxygen vacancies as well as strong H2 and CO2 activation properties. Consequently, the NiSm-Ps catalyst achieved a high CO2 conversion of 80.1% at 400 degrees C and large TOFCO2 of 4.08 x 10-3 at 220 degrees C. Additionally, NiSm-Ps exhibited excellent long-term stability and anti-sintering property. In short, the formation of Sm2Si2O7 was very crucial for the Ni-Sm/SiO2 catalyst and could further improve the promotion effect of Sm species for CO2 methanation.