Electron paramagnetic resonance study of chromosilicalite

Abstract

An electron paramagnetic resonance (EPR) study of crystalline chromosilicalite has been presented with the purpose of characterization of t h e distribution of Cr3+ sites in the solid. In addition, a deconvolution process is described whereby the EPR parameters can be analysed. 135.

Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides

“…The synthesis and characterization of chromium-substituted molecular sieves have only recently received special attention from researchers working in the field of molecular sieve science. Consequently, only a limited number of detailed papers − ,−,− and some patents − have appeared in the literature, which report the synthesis and characterization of Cr-containing AlPO's (CrAPO- n ) and silicalite (Cr silicalite) materials. The applied characterization techniques for studying these crystalline materials are XRD, SEM, DRS, ESR, NMR, and IR.…”

“…Besides this signal, a broad and positive lobe around g ) 4 is observed. This signal has some similarities with the δ-signal on amorphous supports and can be simulated by using high zero field parameters D and E. In view of the work on Cr silicalite of Nakamura et al, 130 lattice-substituted Cr 3+ cannot be excluded. Also Mosser et al 144 and Gaite and Mosser 145 have shown that pseudooctahedral Cr 3+ in kaolinite materials gives a g ) 4.0 signal.…”

“…[125][126] In the case of calcined Cr silicalite, Cr can be easily washed off from the crystalline material, suggesting a weak interaction between silicalite and Cr and a high solubility of Cr in the aqueous phase. 123 Although several authors [123][124][130][131] claim the isomorphous substitution of Cr in molecular sieves, no spectroscopic signatures of lattice substituted Cr have been available up to now in the literature. Only for CrAPO-14, an aluminophosphate with octahedral framework sites, is it clearly shown by single crystal XRD measurements that 4-5% of the octahedral sites are occupied by Cr 3+ ions.…”

“…Consequently, only a limited number of detailed papers [123][124][125][126][130][131][137][138][139][140][141] and some patents [142][143] have appeared in the literature, which report the synthesis and characterization of Cr-containing AlPO's (CrAPOn) and silicalite (Cr silicalite) materials. The applied characterization techniques for studying these crystalline materials are XRD, SEM, DRS, ESR, NMR, and IR.…”

Electron spin resonance spectroscopy

“…Three distinguished Cr3+ (d3) ESR signals are observed in molecular sieves, independently of their type and composition [63][64][65][66]:…”