Abstract
The viability of the Power-to-Gas (PtG) concept is strongly dependent on the development of highly active and stable methanation catalysts obtained from cheap and abundant elements. In this paper, the promotional effect of MnO on Ni catalysts supported on silica-modified γ-Al2O3 (SA) was investigated in CO2 and CO methanation on catalysts with Mn/Ni atomic ratios between 0 and 0.25. Significantly higher methanation rates and CH4 selectivities were obtained for Mn-promoted compositions compared to Ni-only catalysts. The optimal NiMn/SA (Mn/Ni = 0.25) catalyst exhibited improved stability compared with unpromoted Ni/SA at 20 bar. The nature of the catalyst precursor and active catalyst was studied with STEM-EDX, XPS, and X-ray absorption spectroscopy (XAS). Evidence of a mixed Ni-Mn oxide in the catalyst precursor was obtained by EXAFS. EXAFS measurements revealed that the reduced catalyst consisted of metallic Ni particles and small oxidic Mn2+ species. Moreover, Mn addition improved the Ni dispersion and enhanced the Ni2+ reducibility by weakening the interaction between the Ni-oxide precursor and the support. A mechanistic study involving IR spectroscopy and steady-state isotopic (13CO2) transient kinetic analysis (SSITKA) showed that the presence of Mn enhanced CO2 adsorption and activation.
Highlights
As the world transitions towards a renewable energy-based economy, major challenges involving energy storage and transportation must be addressed
We investigated the influence of Mn on Ni/SiO2-Al2O3 catalysts in CO2 methanation
Our study shows that a higher Mn/Ni ratio leads to increased CO2 and CO methanation activity
Summary
As the world transitions towards a renewable energy-based economy, major challenges involving energy storage and transportation must be addressed. The primary drawback of renewables such as wind and solar is their fluctuating and intermittent nature, which leads to the need to store substantial amounts of energy to balance short-term and long-term seasonal variations [1]. The Power-to-Gas (PtG) concept has been proposed as a strategy to store excess renewable energy in the form of synthetic natural gas [2]. PtG involves the hydrogenation of CO2 to CH4 with H2 obtained from renewable energy forms, e.g. through water electrolysis using electricity from wind and solar. The advantages of synthetic natural gas are high energy density and compatibility with the current energy infrastructure, which includes an efficient grid for distribution [3,4,5].
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