CO2 and steam-CO2 reforming of ethanol over CuО/Al2O3 catalysts: Influence of additives on catalyst coking

The effect of γ-Al₂O₃ modification with CeO₂ and La₂O₃ oxides on the catalytic and performance characteristics of copper catalysts in CO₂ reforming and steam–CO₂ reforming of ethanol is investigated. Catalysts with compositions of 10 wt% CuO/Al₂O₃, 10 wt% CuO/2 wt% CeO₂–Al₂O₃ and 10 wt% CuO/2 wt% La₂O₃–Al₂O₃ were synthesized, characterized by TPD-CO₂, TPR-H₂, TPO, TGA/DTA and XRD techniques, and tested in the temperature range of 500–800 °C. The addition of La₂O₃ was shown to generate the strongest basic sites and suppress the formation of the CuAl₂O₄ spinel phase, resulting in an optimal combination of high CO₂ conversion (95 %), maximum hydrogen concentration (55.3 vol%), and minimal coking under steam–CO₂ reforming conditions. In contrast, CeO₂ addition enhances oxygen mobility and promotes ethanol dehydration activity but leads to the highest ethylene yield (67.5 vol%) and the greatest coke deposition (167 mgC/gcat), particularly in the presence of steam. A linear correlation (R² ≈ 0.98) between ethylene yield and the amount of deposited carbon was identified, indicating the key role of ethylene as a coke precursor in the investigated systems. Thermogravimetric analysis of spent catalysts revealed that the La-modified catalyst accumulated the lowest amount of predominantly reactive carbon species and exhibited the lowest deactivation rate. The obtained results establish the relationship between basicity, redox properties, and coking tendency in CuO/Al₂O₃–CeO₂/La₂O₃ systems, providing a rational basis for the design of stable copper catalysts for ethanol reforming with simultaneous CO₂ utilization. • First systematic comparison of La₂O₃ and CeO₂ promoters on CuO/Al₂O₃ in CO₂ and steam-CO₂ ethanol reforming. • La₂O₃ suppresses CuAl₂O₄ spinel, enables 95% CO₂ conversion and 55.3% H₂ yield with minimal carbon deposition. • CeO₂ increases oxygen mobility and ethylene output (67.5 vol%) but maximizes coke (167 mgC/g), R²=0.98 ethylene-coke link. • La-modified catalyst accumulates minimum reactive coke and exhibits slowest deactivation rate in extended cycles. • Steam enhances coking on Ce-catalysts, acid-base and redox balance critical for stable Cu/CO₂ utilization catalysts.