Novel Rate Constants for a Catalytic Hydrogenation Reaction of Propylene Obtained by a Frequency Response Method

Article abstract of DOI:10.1021/j100051a009

"Reaction rate (or FR) spectra" of a catalytic hydrogenation of propylene over Pt or Rh at 314 K were observed in a cell reactor composed of a proton-conducting membrane.It is shown that a variety of the spectra can be reproduced well by "characteristic functions", K^*_H(ω) and K^*_C(ω), which may be derived from a three-stage model composed of five elementary steps: X(g) -->/<-- A_X(a) -->/<-- B_X(a) --> propane (X: hydrogen or propylene), where X denotes the gaseous molecule; A_X and B_X are the first and second intermediate adsorbed species.Seven rate constants concerning these five steps were evaluated by matching K^*_H(ω) or K^*_C(ω) to the spectrum; five of them, k_PX, k_-AX, k_AX, k_-BX, and k_BX, are ordinary rate constants, while the other two, l_-BX and l_BX, are novel ones.Since all these constants except k_PX are independent of the amounts of catalyst, they are characteristic of active sites and can be compared with each other.On the basis of these constants, kinetic details have been discussed; for instance, mean residence times of A_X and B_X, τ_AX and τ_BX, respectively, were determined by (k_-AX + k_AX)^-1 and (k_-BX + k_BX)^-1, resulting in (in second units) τ_AH ca. 0.3 and τ_BH ca. 3 for hydrogen and τ_AC ca. 3 for propylene over Pt, while over Rh they were τ_AH ca. 1 and τ_BH ca. 3; τ_AC ca. 10² and τ_BC ca. 10².The nondimensional rate constants, l_-BX and l_BX, were indispensable to reproduce the various FR spectra; l_-BH and l_BH were positive, whereas l_-BC and l_BC were negative over both catalysts, which suggests heat effects.

Full text of DOI:10.1021/j100051a009

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Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.