ELECTRON-PARAMAGNETIC RESONANCE STUDY OF CHROMOSILICALITE

An electron paramagnetic resonance (EPR) study of crystalline chromosilicalite has been presented with the purpose of characterization of the distribution of Cr3+ sites in the solid. In addition, a deconvolution process is described whereby the EPR parameters can be analysed.88142071207

Journal of the Chemical Society, Chemical Communications

p. 922-923Incorporation of oxygen to crystalline zeolitic chromosilicates, with oxidation of anchored Cr"' to non-interacting CrVl species, has been confirmed by photoacoustic spectroscopy; the dichromate anion being extracted from the chromosilicate with water and identified by precipitation of AgCr04 and oxidation to Cr05

Journal of the Chemical Society, Faraday Transactions

p. 2071-2073The catalytic importance of chromium has prompted numerous attempts to introduce chromium cations in zeolites. For example, Naccache and Ben Taarit,' Atanasova et aL2 and Pearce et d3 have investigated the Cr species mainly in A, X, and Y zeolites, whereas Hemidy et aL4 and Kucherov and Slinkin' reported results for the Cr-mordenite system. In a recent communication6 we reported the incorporation of Cr3+ in the structural positions of ZSM-5 type zeolites, and recently we have demonstrated the incorporation of oxygen in this zeolite with oxidation of anchored Cr3+ to noninteracting Cr6+ species.' Here an EPR study of crystalline chromosilicalite is presented with the purpose of further characterizing the distributon of each Cr3+ site in the solid. Such characterization is a necessary prelude to establishing the chromosilicalite activity as a catalyst in the production of alkenes. In addition a deconvolution process is described whereby the EPR parameters could be analysed. This method proved to be quite successful, and the results provide evidence that Cr3+ ions are at least in two substitutional-like or highly distorted sites and in another one outside the silicon framework.Salvado

Metal Complexes as Structure-Directing Agents for Zeolites and Related Microporous Materials

Metal complexes can act as structure-directing agents (SDAs) for zeolites and zeotypes, either alone or together with additional SDAs in dual-templating approaches. Such complexes include organometallic cobaltocenium ions, alkali metal crown ether complexes, first-row transition-metal (Fe, Co, Ni, Cu) poly-amines and thiol-complexed second-and third-row transition metals (Pd, Pt). Their inclusion has been demonstrated in some cases by crystallographic methods but more commonly by spectroscopy (UV-visible, X-ray absorption, M€ossbauer). The unique feature of this class of template is that they can not only direct crystallisation but also give solids with homogeneously distributed metal cations or metal oxide species upon calcination, precluding the need for an additional post-synthesis modification step. Materials prepared via this ‘one-pot’ synthetic route have been shown to give shape-selective catalysts for reactions such as the selective catalytic reduction of NOx with ammonia and the hydrogenation, dehydration and oxidative dehydrogenation of small hydrocarbons and oxygenates.</p