A structure sensitivity approach to temperature programmed desorption

A novel approach for explaining the effect of the metal cluster size on Temperature Programmed Desorption (TPD) from supported catalysts is described. Based on the assumption that metal clusters have regular cuboctahedral geometry, it was possible to develop a model that describes how three dimensional aspects of the metal clusters may affect the TPD profiles. Depending on the way that the metal clusters are assumed to be arranged in the surface, two different approaches are described to account for desorption. The first one, named Monocluster Model, considers a surface with a narrow cluster size distribution in which an average cluster diameter reasonably well describes the cluster population. A more complete approach, named Multicluster Model, explains desorption based on the cluster size distribution of the metal sites. TPD curves of ammonia from different platinum supported carbon materials were numerically treated and compared with the geometrical information obtained from Transition Electron Microscopy. The results displayed a reasonable agreement, indicating that TPD curves should be interpreted taking into account the metal cluster size.