High-temperature calcination-induced Cu–Al–O precursor environments enable accessible Cu sites in Cu/Al2O3 catalysts for the reverse water–gas shift reaction

High-temperature calcination was investigated as a precursor-engineering strategy to enhance Cu-site accessibility in Cu/Al2O3 catalysts for the reverse water–gas shift reaction. Cu/Al2O3 catalysts with different Cu loadings were calcined at 950 oC, and a 15 wt% Cu catalyst calcined at 600 oC was prepared for comparison. Although 950 oC calcination decreased the specific surface area, XRD, Raman spectroscopy, and H2-TPR showed that it diminished crystalline CuO-like features and generated strongly interacting Cu–Al–O precursor environments. After H2 reduction, 15Cu/Al2O3(950 oC) exhibited weaker metallic Cu reflections and less localized Cu-containing domains than 15Cu/Al2O3(600 oC). N2O titration further revealed that 15Cu/Al2O3(950 oC) had the highest N2O consumption of 47.5 μmol gcat-1, approximately 4.2 times higher than that of 15Cu/Al2O3(600 oC), indicating a larger population of accessible N2O-reactive reduced Cu sites. Consequently, 15Cu/Al2O3(950 oC) showed the highest CO2 conversion at 500 oC with approximately 100% CO selectivity. Similar apparent activation energies for the two 15Cu catalysts suggest that the enhanced activity mainly originated from increased Cu-site accessibility rather than a changed apparent reaction pathway. During the 50 h time-on-stream test, 15Cu/Al2O3(950 oC) maintained higher activity, while post-reaction analyses confirmed smaller spent Cu crystallites than those of 15Cu/Al2O3(600 oC). These results demonstrate that high-temperature-derived Cu–Al–O precursor environments improve selective RWGSR activity by increasing accessible reduced Cu sites.