Abstract
Abstract
Ni-based catalysts intrinsically favor CO2 hydrogenation methanation at low temperatures (200–400 °C) via a formate mediated pathway, affording CH4 selectivity quite high (above 98%). Herein, we reported that K-30%Ni/MgO nanosheet catalyst modified with alkali metals markedly altered the reaction pathways in the low-temperature hydrogenation of CO2. At 350°C and H2/CO2 =3, the CO formation rate reached a maximum of 360.3 mmol·gcat⁻1·h⁻1, CO2 conversion attained 27.0% (equilibrium conversion of 29.8%), and CO selectivity remained above 97%, no significant decline was observed after 320 h continuous operation. This performance surpasses that of most previously reported noble-metal (Pt, Ru, and Pd) catalysts for low-temperature reverse water gas shift reaction (RWGS). Comprehensive characterization, together with in situ DRIFTS and 13C isotope-labeling experiments, reveals that K redirects CO2 hydrogenation through a carbonate–bicarbonate mediated cycle pathway, in which the adsorbed carbonate species are hydrogenated into bicarbonate intermediates that directly produce CO, thereby suppressing the formation of the methanation-related formate. Meanwhile, surface K2CO3 electronically modifies the Ni active sites, weakening deep hydrogenation and facilitating CO desorption, thereby rendering RWGS the dominant reaction pathway. This work provides mechanistic insights into alkali-metal-promoted CO2 hydrogenation and a rational strategy for designing highly efficient low-temperature RWGS catalysts.