Electronic Properties and Catalytic Activity

Recently, we reported that an Fe supported zeolite (FeHY-1) shows high activity for acidic reactions such as toluene disproportionation and resid hydrocracking in the presence of H2S [1,2]. Investigations using electron spin resonance (ESR), Fourier transform infrared spectroscopy (FT-IR), MiJssbauer and transmission electron microscopy (TEM) revealed that superfine ferric oxide cluster interacts with the zeolite framework in the super-cage of Y-type zeolites [3,4]. Furthermore, we reported change in physicochemical properties and catalytic activities for toluene disproportionation during the sample preparation period[5]. It was revealed that the activation of the catalyst was closely related with interaction between the iron cluster and the zeolite framework. In this work, we will report the effect of preparation conditions on the physicochemical properties and activity for toluene disproportionation in the presence of 82. ... 

Despite various attempts, no single universal correlation between bulk properties and catalytic activity of solids has been found. It is now recognized that the geometric factor and the electronic factor cannot be separated from one another and that catalytic activity should be considered along with catalyst selectivity to arrive at an understanding of heterogeneous catalysis (Sachtler, 1981). 

Recent advances in the preparation of ceria-based gold catalysts for hydrogen production by the WGS and PROX reactions are reviewed in this chapter. Considerable emphasis is placed on the catalyst characterization by a number of physicochemical methods X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The relation between the structure, properties, and catalytic activity, as well as the nature of the active sites is also discussed. 

The active site of LADH contains an Asp-His-Zn triad (see Figure 11). This pattern is quite common in zinc-enzymes. The aspartate affects the structure, electronic properties and energetics of the active site and thus the catalytic activity. Indeed, Asp49 is conserved in all mammalian ADHs . 

Biomaterials such as proteins/enzymes or DNA display highly selective catalytic and recognition properties. Au nanoparticles or nanorods show electronic, photonic and catalytic properties. The convergence of both types of materials gives rise to Au NP-biomolecule hybrids that represent a very active research area. The combination of properties leads to the appearance of biosensors due to the optical or electrical transduction of biological phenomena. Moreover, multifunctional Au NP-peptide hybrids can be used for targeting nuclear cells where genetic information is stored and could be useful for biomedical applications [146]. 

Let us emphasize again that this correlation does not pretend to establish a proportionality between semiconductivity and catalytic activity. It shows however that certain changes in electronic structure of a solid which can be brought about by selected impurities are reflected upon both the conducting and catalytic properties of a solid. A deeper analysis is required if the direction of, or the change in, catalytic activity is to be predicted on a rational basis. In the last analysis these changes... 

The political justification for transition metal cluster chemistry is the assumption that clusters are models in which metallic properties may be more easily studied than in the metals themselves. These properties include electronic phenomena such as color and conductivities as well as surface phenomena, such as atom arrangements and catalytic activities. Thus, there are two main lines of cluster research. The more academic line leads to the search for new types of clusters and their structure and bonding, whereas the more practical line leads to the investigation of reactivities with the hope that clusters may open catalytic pathways that neither plain metals nor mononuclear catalysts can provide. The interdependence of both lines is obvious. 

We have chosen to present a review of experiments and the theory of surface enrichment before dealing with the catalytic properties of alloys and discussing the existing evidence for the relevance of changes in the electron distribution in catalytically active atoms. 

Since the electronic properties of solids depend on the crystal structure, the transition from the crystalline to the amorphous state is expected to result in some modification of electronic (and surface) properties. Amorphous materials have first been used in catalysis [558-560] where some evidence for higher activity has been obtained [561]. In particular, hydrogenation reactions are catalyzed by this class of materials [562]. Studies on the H recombination reaction are also available [563]. However, the evidence that the amorphous state is really the origin of enhanced catalytic activity is not completely clear [562, 564]. These materials have the peculiarity that their surface is relatively homogeneous for a solid and in particular it is free from grain boundaries [565, 566]. Therefore, they have been suggested [562] as ideal model surfaces for studying elementary catalytic reactions, since they can be prepared with controlled electronic properties and controlled dispersion. Nevertheless, many prob-... 

The study of these catalysts may sharpen our insight into the phenomenon of catalysis itself however. We have seen that the study of electron donor/ac-ceptor complexes for the activation of molecular hydrogen has shown many correlations between physical properties of the acceptor and catalytic activity. 

Arylamines are commonplace. They are part of molecules with medicinally important properties, of molecules with structurally interesting properties, of materials with important electronic properties, and of transition metal complexes with catalytic activity. An aryl-nitrogen linkage is present in nitrogen heterocydes such as indoles [1, 2] and benzopyr-azoles, conjugated polymers such as polyanilines [3-9], and readily oxidizable triarylamines used in electronic applications [10-13]. The ability of aryl halides and triflates to form arylamines allows a single group to be used as a synthetic intermediate in aromatic carbon-... 

Properties of inorganic nanotubes such as those of MoS2 have been investigated to some extent. However, by and large, there is much to be studied with respect to the electronic, optical and other properties of most of the inorganic nanotubes. Properties such as sorption, hydrogen storage and catalytic activity are worthy of exploration. Mechanical properties of BN, B-N-C and related nanotubes are also worthy of study. 

The electron microscope offers a unique approach for measuring individual nano-sized volumes which may be catalytically active as opposed to the averaging method employed by spectroscopic techniques. It is just this ability of being able to observe and measure directly small crystallites or nano-volumes of a catalyst support that sets the microscope apart from other analyses. There have been many studies reported in the literature over the past fifteen years which emphasize the use of analytical and transmission electron microscopy in the characterization of catalysts. Reviews (1-5) of these studies emphasize the relationship between the structure of the site and catalytic activity and selectivity. Most commercial catalysts do not readily permit such clear distinction of physical properties with performance. The importance of establishing the proximity of elements, elemental distribution and component particle size is often overlooked as vital information in the design and evaluation of catalysts. For example, this interactive approach was successfully used in the development of a Fischer-Tropsch catalyst (6). Although some measurements on commercial catalysts can be made routinely with a STEM, there are complex catalysts which require... 

Iron sulfur clusters appear in a great many proteins as both electron-transport and enzymatic sites see Iron-Sulfur Proteins), for this reason there has been great interest for 30 years in the development and nnderstanding of iron-snlfur model complexes. Both stmctnre and properties of synthetic analogs of 1-, 2-, 3-, and 4-iron protein active sites have been stndied extensively. This article will address the stmctnral and chemical properties, synthesis, and catalytic activity of these synthetic analogs, as compared to the native protein-bound iron-sulfur cores. 

The LDOS-based frontier orbital model is different from the simpler collective-electron model, in which all local information is averaged out. In the context of alloys. Ponec and Bond (23. p. 451). stated that it must be clear to the reader that (the collective electron model of catalytic activity of alloys] has now been consigned to the trash can of science. . . [because of] the discovery that, more in tune with chemists intuition, the atoms in an alloy retain their identity more or less completely. Such local properties disappear from the collective-electron model in which it was supposed that the available electrons were equally shared by aU the atoms present, and that. .. the density of states at the Fermi surface or some related... 

This paper describes the use of polydentate ligands to optimize the performance of palladium catalysts for CO2 reduction and to probe mechanistic aspects of catalytic reactions. Polydentate ligands can be used to precisely control coordination environments, electronic properties, and specific steric interactions that can lead to new insights into the relationship between catalyst structure and activity. 

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