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A general method for determining the role of spectroscopically observed species in reaction mechanisms: Analysis of coverage transients (ACT)

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Abstract.
A kinetic method is described to determine the role of adsorbed intermediates in heterogeneous reaction
mechanisms. The method, denoted as analysis of coverage transients (ACT), involves comparing the time
response of a spectroscopically observed species in an inert gas and a reactive gas to differentiate
between adsorption–desorption processes and reaction. The method is applied in a kinetic study of
pyridine hydrodenitrogenation (HDN) on a 12.2 wt% silica-supported nickel phosphide (Ni2P/SiO2)
catalyst at 423 K and atmospheric pressure. In situ Fourier transform infrared spectroscopy (FTIR)
measurements of pyridine adsorbed on Ni2P revealed the formation of a pyridinium surface intermediate.
The concentration of the pyridinium intermediate increased with pyridine partial pressure and decreased
in the presence of hydrogen, suggesting that it was a reaction intermediate. However, transient and
steady-state kinetic measurements showed that the rate of reaction of the intermediate did not
correspond to the overall reaction rate, and it is concluded that the pyridinium intermediate is not
directly involved in the HDN reaction of pyridine over Ni2P. The studies demonstrate that mere
observation of an adsorbed surface species at reaction conditions is not sufficient to prove that it is a
reaction intermediate. The ACT method has potential as it can be used with any type of spectroscopy, as
long as the surface coverage can be calibrated.

Keywords:
Hydrodenitrogenation
Mechanism, transient coverage analysis
In situ FTIR
Pyridine
2,3,4,5-Tetrahydropyridine
Nickel phosphide

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Informasi Detail

Judul Seri

Journal of Catalysis

No. Panggil

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Penerbit

London : Elsevier Inc.., 2009

Deskripsi Fisik

Journal of Catalysis 263 (2009) 359–371

Bahasa

English

ISBN/ISSN

00219517

Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

KIMIA

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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