Catalytic conversions of chloroolefines over iron oxide nanoparticles 3. Electronic and magnetic properties of γ-Fe2O3 nanoparticles immobilized on different silicas

Abstract

Catalytic properties of superparamagnetic γ ferric oxide nanoclusters, which are uniform in terms of size and magnetic properties were studied. The catalysts were supported on the activated silica gel matrix (AGM) prepared from the KSK 2 silica gel of globular structure and on the activated silica matrix (ASM) prepared from layered natural vermiculite. The clusters are active in some reactions of chloroolefin conversions: isomerization of dichlorobutenes and alkylation of benzene with allyl chloride. Their activity in these reactions is many times higher that of usual suppоrted catalysts based on α ferric oxide. Analysis of the Mössbauer spectra of the 2.5 wt.% Fe/AGM and 2.5 wt.%Fe/ASM samples before and after the reaction at Т = 3-300 К shows that during the reaction some Fe III ions arranged in ∼2-3 nm γ Fe 2 O 3 nanoclusters magnetically ordered at 6 K are reduced to form a high spin Fe II complex in the paramagnetic state. According to the macroscopic magnetization data (SQUID) of the initial clusters, curves with hysteresis are observed at 2 K in the plots of forward and backward magnetization, while the 2.5 wt.%Fe/ASM catalyst after the reaction at Т = 2 К demonstrates a linear field dependence of the magnetization passing through the coordinate origin. Analysis of the Mössbauer spectra and magnetic properties suggests that during the catalytic reaction the Fe III ions in the γ Fe 2 O 3 nanoclusters interact with chloroolefin with the allylic structure to be partially reduced to the Fe II ions that are bound in a complex containing chloride ions and O II ion(s) of the silicate matrix as ligands. This is a reason, probably, for the high catalytic activity of γ Fe 2 O 3 nanoparticles.

Synthesis and characterization of maghemite nanopowders by chemical precipitation method

“…Among the researchers working in the field of nanotechnology, magnetic nanoparticles have attracted intense experimental activities because of their potential applications in a numerous different industries such as storage of information [4], ferrofluid [5], audio and video recording [6], bioprocess [7] gas sensor [8][9][10][11][12][13], refrigeration systems [14], information storage [15], medical applications [16], magnetic resonance imaging [17], catalyst [18,19], magnetooptic [20], and removal of heavy metals [38,39].…”

Nanocatalysts for Rearrangement Reactions

“…When it was possible to do this, the functionalization of the nanoparticles has also been determined employing nuclear magnetic resonance techniques. Changes in the electronic and magnetic properties of the catalysts during the reactions were in some cases examined by Mössbauer spectroscopy, [36][37][38] using measurements of macroscopic magnetization (SQUID) to determine the static magnetic susceptibility.…”

“…In this sense, Rostovshchikova and coworkers have described a large series of nanocatalysts able to perform the selective isomerization of 3,4-dichlorobut-1-ene 2 into trans-1,4-dichlorobut-2-ene 3 (Scheme 8.4). In particular, employing Fe(III) oxideNPs (␣-Fe 2 O 3 or ␥ -Fe 2 O 3 ) supported on silica [36][37][38] or stabilized on the surface of polymeric matrices, 62, 63 as well as copper, nickel, and palladium nanostructured metal films supported on the surface of thermally oxidized silicon, 64-66 2 could be converted into 3 with almost complete stereoselectivity (only 2% of the cis-isomer 4 was observed) and high turnover frequencies (up to 4500 h −1 ).…”