Alkali Promotion in the Formation of CH₄ from CO₂ and Renewably Produced H₂ over Supported Ni Catalysts

Abstract

In Power-to-Methane (PtM) plants, the renewable electricity supply can be stabilized by using green electrons to produce H 2 via H 2 O electrolysis, which is subsequently used to hydrogenate CO 2 into CH 4 . In this work PtM is studied in a cascade fashion, from simulated solar light to methane production in an all-inone setup, which was newly developed for this work. This setup was used to assess the effects of H 2 stream purity on the activity of Ni/SiO 2 catalysts in CO 2 methanation. An activity effect in downstream methanation is shown to be onset by aerosols that evolve from the electrochemical splitting of water. Small amounts of K are shown to affect CH 4 production positively, but only if they are deposited in situ, via KOH aerosols. K-doped Ni/ SiO 2 catalysts prepared in an ex situ manner, by impregnation with a KOH solution, showed a decrease in activity, while the same amount of KOH was deposited. Operando FT-IR spectroscopy reveals that increased back-donation to CO-containing intermediates and carbonates formation likely causes catalyst deactivation in ex situ samples as often reported in literature for Ni/SiO 2 catalysts. The mechanism for in situ promotion is either an increased rate in the hydrogenation of CH x (X = 0-3) fragments, or a more facile water formation or desorption as CO-containing reaction intermediates are unaffected by in situ promotion. These results are relevant to PtM from a fundamental standpoint explaining the effect of potassium on nickel methanation, but also from a practical standpoint as the presented effect of in situ promotion is difficult to achieve via standard synthesis methods.

The Role of Alkali and Alkaline Earth Metals in the CO2 Methanation Reaction and the Combined Capture and Methanation of CO2

“…Another interesting study that includes an in-situ KOH modification of a Ni/SiO 2 methanation catalyst has been conducted by Vogt et al [49]. The authors first created a setup that produced hydrogen through solar driven H 2 O electrolysis from a KOH-based alkaline electrolyzer.…”

Promising Catalytic Systems for CO2 Hydrogenation into CH4: A Review of Recent Studies

“…Indeed, the positive effect of this metal was further enhanced when intensifying its loading since it revealed much higher resistance to Ni nanoparticles sintering. Finally, Vogt et al [42] evaluated the effect of KOH (derived from H 2 production process) in the activity of Ni-based SiO 2 catalysts. Authors applied in situ (setup combining H 2 O electrolysis and CO 2 methanation steps) and ex situ (KOH impregnation over Ni/SiO 2 catalysts) strategies and verified that, while the first increases the obtained catalytic performances, the second leads to catalysts deactivation.…”

The Recent Progress on Supported and Recyclable Nickel Catalysts towards Organic Transformations: A Review

“…Recently, an alkali promoted hydrogenation of CO 2 to CH 4 was achieved by Vogt et al. by employing K‐ doped Ni supported on SiO 2 surface [101] . The generation rate of in‐situ hydrogen was dramatically changed with the concentration of K and the support itself.…”