Clusters interaction with framework

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. ... 

Fig. 15.8 Top side row B3-LYP/6-31+G(d,p) optimized clusters mimicking Lewis acidic Al(III) sites. LS model mimics highly strained Al(lll)atoms, typical of defects present in H-BEA zeolites LC cluster simulates the Al(III) atoms coordinating an additional nearby framework O atom. Bottom side row B3-LYP/6-31+G(d,p) optimized structures of the LS and LC clusters interacting with one H2O molecule (LSW and LCW, respectively). Atomic symbols are reported in the model cluster LS. Adapted from ref. [7] Figs. 2 and 3...

Metal clusters (M ,) can be roughly described as small pieces of metal,but closer studies show that their atomic and electronic structures deviate from those of bulk metals either because of intrinsic size effects (deviation from normal electronic structure at very small nuclearities) or because of their interaction with framework anions and extra-framework species including cations. Clusters can be naked or bonded to various extra-framework ligands. They may be charged as a result of incomplete reduction or of interactions (inductive and/or field effects) with framework or extra-framework species. Clusters can involve two metals homogeneously alloyed or segregated. 

Obviously we may expect that the simple two- and three-particle collision approximation discussed in the previous sections is not appropriate, because a large number of particles always interact simultaneously. Formally this approximation leads to divergencies. In the previous sections we used in a systematic way cluster expansions for the two- and three-particle density operator in order to include two-particle bound states and their relevant interaction in three- and four-particle clusters. In the framework of that consideration we started with the elementary particles (e, p) and their interactions. The bound states turned out to be special states, and, especially, scattering states were dealt with in a consistent manner. 

Silvestrelli5 reached a similar conclusion for Si(001) -(2x1) interaction with ethanol in the framework of a periodic slab approach, where the Car - Parrinello method was used, instead of a cluster model. Quantitatively, substantial differences... 

The reaction of M3(CO)12 with both open-chain and cyclic poly-alkenes has attracted some attention, especially in the case of Ru3(CO)i2. In most of the examples reported, the organic fragment bonds to the metal framework in such a way as to interact with more than one of the three metal atoms (68-77). There are some exceptions to this general statement, however. One is the reaction of Ru3(CO)j 2 with cyclopentadiene, in which a mononuclear complex is obtained (78). In other cases, tetranuclear and hexanuclear compounds are obtained (79 81). Cluster breakdown has also been observed in the case of a rhodium complex upon reaction with ethylene (55) as shown in Fig. 3. 

The overwhelming majority of the theoretical studies were performed on cluster models of the catalytic site, hi spite of the fact that the role of space confinement and the secondary interactions with the framework atoms is well-known, there are only a few electronic structure calculations on lattice models involving hydrocarbons, using either periodic DFT calculations, or embedding methods. In this brief account of the subject we attempt to overview some of the recent computational results of the literature and present some new data obtained from ab initio DFT pseudopotential plane wave calculations on Cl - C4 alkanes in the chabazite framework. 

The conjugate base of a cluster generated by deprotonation (see Section 5.1) is a Lewis base. Any metal-metal, metal boron, or boron boron bond is a potential Lewis base. The former have considerable nucleophilic character if anionic and effectively interact with electrophiles more complex than the proton. As the site of basicity is associated with framework bonding, this reaction type results in cluster building, for... 

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