Characterization of Ag/α-Al₂O₃ olefin epoxidation catalysts containing promoters and co-promoters using pulse hydrogen titration methods

A series of Cs and Cs + Re promoted 12 wt% Ag/α-Al₂O₃ catalysts were prepared and characterized by H₂ pulse titration of O-precovered Ag to measure active Ag site concentrations. Temperature programmed reduction (TPR) at temperatures up to 500 °C was performed on α-Al₂O₃ supported 3–4 wt% Cs, Re, or Mo only catalysts to confirm the metal–oxygen bonds of the promoters were not reactive during titration of Ag-O surface at 170 °C; absence of H₂ uptake during H₂ titration for these samples confirmed the TPR results. H₂ pulse titration results of 0 to 7.5 μmol Cs promoted, 12 wt% Ag/α-Al₂O₃ catalysts showed non-preferential deposition of Cs on Ag and α-Al₂O₃ surfaces. However, when Cs (2.6 μmol)–12 wt% Ag/α-Al₂O₃ catalyst was promoted with ≥1.3 μmol of Re, titration results showed preferential deposition of Re on Ag sites, presumably to lower overall surface free energy of the Re-Ag-Al₂O₃ system.