Characterization of metal segregation in Pt–Re/Al2O3 reforming catalysts Original Research Article

Mono- and bimetallic platinum–rhenium reforming catalysts with the content of each metal of 0.3 wt.% were studied by H2 and O2 adsorption, TPR and X-ray absorption techniques. It has been demonstrated that combination of hydrogen and oxygen adsorption at ambient temperature is a sensitive tool to monitor Pt–Re interaction in reforming catalyst. The technique was applied to the investigation of the effect of various pretreatments on the state of Pt and Re in bimetallic catalysts. It was shown that the degree of surface hydroxylation essentially affects aggregation or segregation of Pt and Re during reduction step. Thus, pretreatments at severe conditions, leading to dehydroxylation of the alumina surface, resulted in Pt–Re segregation evidenced by an increase of H2 adsorption due to higher amount of exposed Pt atoms and a decrease of O2 adsorption due to a smaller fraction of Re atoms in close contact to Pt. On the contrary, treatments at moderate conditions, preserving surface hydroxyl groups, favored the transport of ReOx species to Pt during the reduction step and resulted in the aggregation of metals followed by a decrease of H2 adsorption and an increase of O2 adsorption. These conclusions were confirmed by TPR and X-ray adsorption experiments.