An insight into the mechanism of selective mono-N-methylation of aniline on Cu1-xZnxFe2O4: a DRIFTS study

Vijayaraj, Munusamy ; Murugan, Balasundaram ; Umbarkar, Shubhangi ; Hegde, Sooryakant G. ; Gopinath, Chinnakonda S. (2005) An insight into the mechanism of selective mono-N-methylation of aniline on Cu1-xZnxFe2O4: a DRIFTS study Journal of Molecular Catalysis A: Chemical, 231 (1-2). pp. 169-180. ISSN 1381-1169

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Mechanism of selective mono-N-methylation of aniline with methanol on Cu1-xZnxFe2O4 catalysts was investigated in detail. The interaction of reactants (aniline, methanol and methanol:aniline) and possible products (N-methylaniline (NMA), N,N-dimethylaniline (DMA) and o-toluidine (OT)) on catalysts surface was studied by temperature-dependent in situ FTIR spectroscopy. Methanol adsorbs dissociatively over catalysts surface at 373 K as methoxy species and is oxidized to formate species at high temperature through dioxymethylene and/or formaldehyde as a surface intermediate species. On the other hand, adsorption of aniline:methanol mixtures shows that methanol oxidation was completely hindered in the presence of aniline. Aniline adsorbs on the Lewis acid sites at ≤373 K with phenyl ring oriented in a perpendicular manner to the catalyst surface; however, N—H bond scission occurs above 373 K. A comparison of adsorbed NMA and methanol:aniline (3:1) mixture on Cu0.5Zn0.5Fe2O4 shows NMA forms from the reaction mixture at 473 K. However, maximum activity at 573 K in catalytic reaction studies suggests that desorption limits the methylation kinetics. FTIR study displays stable aniline and methyl species on ZnFe2O4 even at 573 K; however, no methyl species is detected on Cu0.95Zn0.05Fe2O4 at 473 K due to methanol reforming reaction and that limits the overall reaction and hence low catalytic activity. It is proposed that methanol is protonated on catalysts surface by the labile H+ due to N—H bond scission. Co-adsorption of acidity probes with aniline and methanol indicates that aniline methylation takes place at single acid-base site.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Cu1-xZnxFe2O4; Aniline; Methanol; N-methylation; DRIFT; IR; Reaction Mechanism; N-methylaniline; Desorption Limited
ID Code:61863
Deposited On:15 Sep 2011 12:13
Last Modified:15 Sep 2011 12:13

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