Iron, Copper And Tin Incorporated Rice Husk Ash Silica : Preparation, Characterization And Application As Catalysts For Friedel-Crafts Benzoylation Reactions
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Date
2011-07
Authors
Hassan, Ishraga Abdelmoniem
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Abstract
Iron, copper and tin incorporated silica catalysts were prepared via sol-gel
method using the silica extracted from rice husk ash. The modified catalysts were
denoted as RHA-xFe (x = 5, 10, 15 and 20 wt.%), RHA-10Cu and RHA-10Sn.
Prepared catalysts were characterized by various physico-chemical techniques such
as XRD, FT-IR, N2-sorption, AAS, SEM-EDX, TEM, DR UV/Vis, solid state 29Si
MAS NMR, EPR, TGA-FT-IR and FT-IR-pyridine adsorption. The catalysts were
found to be amorphous. Elemental analysis confirmed the presence of the metals in
the silica framework. The acidity studies on the catalysts by using FT-IR-pyridine
adsorption demonstrated that, there is no Brønsted acid sites. However, it has mainly
Lewis acid sites. The catalytic activity of RHA-xFe with different iron loadings was
studied for liquid-phase benzoylation of p-xylene, anisole and toluene with benzoyl
chloride as benzoylating agent. The effect of various reaction parameters such as iron
loadings, catalyst mass, molar ratio of the reactants, reaction temperature, catalyst
type, leaching of metal and catalyst reusability was discussed. Compared to other
iron loadings, RHA-10Fe was found to be the most efficient catalyst in terms of
conversion and selectivity. Comparison of catalytic activity of RHA-10Fe, RHA-
10Cu and RHA-10Sn in the benzoylation reaction of the aromatic compounds under
the optimized reaction conditions was found to be in the order: RHA-10Fe >> RHA-
10Sn > RHA-10Cu. However, the products selectivity followed the order: RHA-
10Fe >> RHA-10Cu > RHA-10Sn for the benzoylation of p-xylene and toluene,
while for the benzoylation of anisole as in the order: RHA-10Fe >> RHA-10Sn >
RHA-10Cu. The homogeneous iron salt (Fe(NO3)3.9H2O) was tested for the reaction
under the optimized conditions, and it showed higher activity over the heterogeneous
catalysts (RHA-10Fe and RHA-10Fe(Cal)), whereas the highest desired product
selectivity was obtained using RHA-10Fe(Cal) in the benzoylation reaction.
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Keywords
Iron, copper and tin incorporated silica catalysts , silica extracted from rice husk ash