一级脱附反应TPD谱的峰高、峰温与脱附活化能的关系

1. 南京大学化学系
• 收稿日期:1986-01-19 修回日期:1986-09-29 发布日期:1987-06-15
• 通讯作者: 杨上闰

RELATIONSHIP BETWEEN PEAK HEIGHT,PEAK TEMPERATURE AND ACTIVATION ENERGY OF DESORPTION IN TPD SPECTRUM OF FIRST ORDER DESORPTION KINETICS

Yang Shangrun

1. Department of Chemistry; Nanjing University
• Received:1986-01-19 Revised:1986-09-29 Published:1987-06-15
• Contact: Yang Shangrun

Abstract: A consulting table method (CTM) of determining E_d according to T_m and h_m is presented. A relationship, which is the basis of this method, between h_m, T_m and E_d in TPD spectrum of first order desorption kinetics is deduced as follows:
h_m/S_m=(k_0/b)exp(- E_d/RT_m)
where h_m, S_m, k_0, b, E_d, R and T_m are peak height, peak area of T≥T_m, pre- exponential factor, heating rate, activation energy of desorption, standard gas cons- tant and peak temperature, respectively. It has been proved that the number of independent variable in the above five variables is 2. The h_m value has a dimension of K~(-1) and may be evaluated by the following equation:
h_m=W_(ABCD)/W_0(T_D-T_A)
where W_(ABCD) is the weight of the paper corresponding to the rectangle ABCD (see Fig.1), W_o is that under the spectrum T_LPT_H, T_D and T_A are the temperatures at D and A, respectively.
The numerical values which show relationships between h_m, T_m and E_d are tabulated in table 1. In this table, the peak temperatures range from 200 K to 1100 K with interval of 10 K and the activation energy of desorpton range from 20 kJ mol~(-1) to 220 kJ mol~(-1) with interval of 20 kJ mol~(-1). The calculation tolerance of the T_m values in the table are generally within ±0.1 K which only causes a slight error in the h_m value. The relative error of interpolation between two points possessing ΔE_d=20 kJ mol~(-1) or ΔT_m=10 K is within 1%. From table 1 and by using interpolation, it is very easy to evaluate the E_d values from a pair of h_m and T_m values which represents the total information of a spectrum.
Considering that the CTM utilizes the whole information of a TPD spectrum and determines E_d without assuming k_0 value, it has advantages that E_d and k_0 may be determined by only one run of TPD experiment, the data treatment may be simple accomplished without any more computer calculation, and the reliability of results is as high as that obtained by the spectrogram superposition method (SSM)~[2].