Single-phase catalysts properties

The question arises, why do bi- or multi-phasic catalysts generally show better activity and selectivity than the active phase alone The aim of this paper is to answer this question by exploring the role of interfacial effects. We shall examine first how the thermodynamic and structural properties of one phase influence its interactions, not only with the gaseous reactants, but also with coexisting solid phases as a result of its bulk, surface, and defect structure. We will also examine the conditions necessary for these interactions and set up a structural classification of the main components of mild oxidation catalysts. This will lead finally to a discussion of the role of interfacial effects in catalyst performance using some illustrative examples. Thermodynamic and Structural Properties of Single Phase Catalysts... 

V-P oxides are known to be efficient for the production of maleic anhydride (abbreviated as MA) from n-butane (1-3). A single-phase (VO2P2O7 has been inferred to be the active catalyst phase (4-6). In addition, the catalytic properties of (VO)2P207 varied depending on the microstructure of (VO)2P207 particles (7,8). Some claimed that the... 

The complexity of designing such catalysts arises because the C-H transformation function wanted is not the property of a bulk solid or a well-defined surface but of defects in phases. Such catalysts resemble their biological counterparts, the enzymes that consist also of a complex matrix holding the active site in place and in suitable electronic isolation. The ability to mimic this principle in heterogeneous catalysis with the concept of single site catalysts [45-47] has led to first academic success but is still far away from practical realization, because of the lack of suitable procedures for synthesis of bulk quantities of highly active material. 

The catalyst l%Pd Au/C (2) was characterised by TEM, HRTEM and EDX spectroscopy. The observations on the morphology and the microstructures of both the phase and the composition highlight its single phase property. The overview of the catalyst (Fig. 1) shows that the nanoparticles are evenly distributed on the active carbon. The inserted histogram of particle size distribution indicates that most particles are smaller than 10 nm in size. The size distribution is described by a Gaussian function centered at 3.4 nm, with 2 % particles oversized (from 10 nm up to 30 nm). 

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