IR-SPECTRAL STUDY OF THE METAL STATE IN LOW-PERCENTAGE ALUMINA-RHENIUM AND ALUMINA-TECHNETIUM 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 H-2 at 500-900-degrees-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 approximately 20-degrees-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 of n-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 H-2 are the precursors of the catalytically active centers in the paraffin dehydrogenation reaction.