Activity of La0.75Sr0.25Cr0.5Mn0.5O3−δ, Ni3Sn2 and Gd-doped CeO2 towards the reverse water-gas shift reaction and carburisation for a high-temperature H2O/CO2 co-electrolysis

Abstract

The syngas mixture of CO and H₂, e.g. from natural gas reforming, is currently an important feedstock supplier for the synthesis of numerous chemicals. In order to minimize fossil source dependency and reduce global warming, alternative processes to produce syngas, such as high-temperature co-electrolysis of H₂O and CO₂ via the internal reverse water-gas shift (RWGS) reaction, may be meaningful. In this study, the influence of the H₂ : CO₂ ratio on the activity, selectivity and stability of the as-prepared La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCrM) and Ni₃Sn₂ as well as commercial Ni and Gd-doped CeO₂ (GDC₂₀) powder materials for the reverse RWGS reaction was investigated in a tubular quartz glass reactor at 700 °C and 800 °C and ambient pressure. The highest conversion factor close to the maximum value of 50% for CO was yielded for the LSCrM, Ni and GDC₂₀ samples by applying a 0.5 : 0.5 H₂ : CO₂ feed ratio at 800 °C. Similar activity was calculated for the Ni₃Sn₂ alloy after normalization to the Ni mass content. Moreover, all the investigated catalysts exhibited higher selectivity for CO and H₂O products than Ni, with which CH₄ molar concentrations up to 0.9% and 2.4% were collected at 800 °C and 700 °C, respectively. The influence of feed pressure on the carburisation process was inspected in a tubular Ni–Cr reactor. Under a carbon-rich gas mixture at 3 bar and 700 °C, large amounts of graphitic carbon were deposited solely on the Ni sample after 100 h of exposure time. After the exposure of the powder materials to 0.5 : 0.5 and 0.9 : 0.1 H₂ : CO₂ atmospheres for 300 h at 700 °C and 10 bar, traces of amorphous carbon were surprisingly detected only on Ni₃Sn₂ powder via Raman microscopy. Thus, because GDC₂₀ ist not active for electrochemical H₂ production, LSCrM or a mixture of both LSCrM and GDC₂₀ materials appears to be the most promising candidate for Ni substitution in high-temperature H₂O/CO₂ co-electrolysis.