N. Bogolowski, B. Sánchez Batalla, B.K. Shin and J.-F. Drillet
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 La0.75Sr0.25Cr0.5Mn0.5O3−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.
