Abstract
AbstractIn Power‐to‐Methane (PtM) plants, the renewable electricity supply can be stabilized by using green electrons to produce H2 via H2O electrolysis, which is subsequently used to hydrogenate CO2 into CH4. In this work PtM is studied in a cascade fashion, from simulated solar light to methane production in an all‐in‐one setup, which was newly developed for this work. This setup was used to assess the effects of H2 stream purity on the activity of Ni/SiO2 catalysts in CO2 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 CH4 production positively, but only if they are deposited in situ, via KOH aerosols. K‐doped Ni/SiO2 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/SiO2 catalysts. The mechanism for in situ promotion is either an increased rate in the hydrogenation of CHx (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.
Highlights
CO-containing reaction intermediates are unaffected by in situ promotion
The effect of in situ doping with KOH-containing aerosols which evolve from hydrogen production on the catalyst samples listed in Table 1 was compared to an ex situ doping procedure where a 0.6 wt % K loading was achieved by impregnation, via suspension of the catalyst materials in a KOH solution and subsequent evaporation
A benchmark 1 M KOH alkaline solution is used for the production of renewable H2 via H2O electrolysis,[14,26] and we focus on its effect on the catalytic hydrogenation of CO2 into
Summary
The setup that we will discuss in this work is far from what an optimized industrial plant would be, mainly due to electrode size constraints and inefficient heating of the methanation reactor, www.chemcatchem.org and because the kinetic conditions applied The water splitting reaction is performed in alkaline media, as the kinetically limiting step in the electrolysis of water – the OER – benefits from a high pH.[14] the aerosols that may be present in the gas feed from the split water may contain alkaline material Literature shows both promoting, and deactivating effects for the addition of alkaline dopants to thermocatalytic methanation reactions,[15,16,17,18,19,20,21,22,23] and relevant reaction steps thereof, such as the Reverse Water-Gas Shift (RWGS). To the best of our knowledge, no systematic study has been performed to distinguish the possible particle-size dependent effect of alkali promotion, while it seems a relevant variable in Table S1, and no study has considered the effect of in situ deposition of potassium onto a Ni-based methanation catalyst as a potential promotor
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