Converting CO2 Into Natural Gas Within the Autoclave: A Kinetic Study on Hydrogenation of Carbonates in Aqueous Solution

Graphical Herein, combination studies were applied to elucidate the reaction mechanism on CO 3 2− hydrogenation into methane at high efficiency in the solvent. We confirmed the reaction is following CO 3 2− to HCOO − , then to CH 4 reaction path and the C−O bond rupture within HCOO − was confirmed to be the kinetically relevant during catalysis. Catalytic conversion of carbon dioxide (CO 2 ) into value-added chemicals is of pivotal importance, well the cost of capturing CO 2 from dilute atmosphere is super challenge. One promising strategy is combining the adsorption and transformation at one step, such as applying alkali solution that could selectively reduce carbonate (CO 3 2− ) as consequences of CO 2 adsorption. Due to complexity of this system, the mechanistic details on controlling the hydrogenation have not been investigated in depth. Herein, Ru/TiO 2 catalyst was applied as a probe to elucidate the mechanism of CO 3 2− activation, in which with thermodynamic and kinetic investigations, a compact Langmuir-Hinshelwood reaction model was established which suggests that the overall rate of CO 3 2− hydrogenation was controlled by a specific C−O bond rupture elementary step within HCOO − and the Ru surface was mainly covered by CO 3 2− or HCOO − at independent conditions. This assumption was further supported by negligible kinetic isotope effects ( k H / k D ≈1), similarity on reaction barriers of CO 3 2− and HCOO − hydrogenation (Δ H ≠ hydr ,Na2CO3 and Δ H ≠ hydr ,HCOONa ) and a non-variation of entropy (Δ S ≠ hydr ≈0). More interestingly, the alkalinity of the solution is certainly like a two sides in a sword and could facilitate the adsorption of CO 2 while hold back catalysis during CO 3 2− hydrogenation.