IR-spectral study of the metal state in low-percentage alumina-rhenium and alumina-technethillm catalysts following high-temperature reductive treatment

The state of Re and Tc in low-percentage alumina-rhenium (0.25 % Re) and aluminatechnetium (0.1 % Tc) catalysts reduced by H₂ at 500–900 °C was studied using IR spectra of the diffuse reflection of the adsorbed CO. A highly dispersed (probably two-dimensional) metal phase with a lowered electron-donating ability due to strong metal—support interaction is present on the surface of these catalysts along with the ionic forms of Re and Tc at +1 and +4 oxidation states. CO adsorbed on such metals in a linear form can be removed by evacuation even at 20°C. The amount of highly dispersed metal phase on the support surface increases monotonically with an increase in the activation temperature of Re/Al₂O₃ and Tc/Al₂O₃. The activity of the catalysts in the dehydrogenation ofn-dodecane varies directly with the concentration of the electron-deficient highly dispersed metal phase. It is therefore concluded that highly dispersed Re⁰ and Tc⁰ formed during high-temperature treatment by H₂ are the precursors of the catalytically active centers in the paraffin dehydrogenation reaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 664–667, April, 1993.