Does Pelletizing Catalysts Influence the Efficiency Number of Activity Measurements? Spectrochemical Engineering Considerations for an Accurate Operando Study
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- 作者：S酶ren B. Rasmussen ; Susana Perez-Ferreras ; Miguel A. Ba帽ares ; Philippe Bazin ; Marco Daturi
- 刊名：ACS Catalysis
- 出版年：2013
- 出版时间：January 4, 2013
- 年：2013
- 卷：3
- 期：1
- 页码：86-94
- 全文大小：452K
- 年卷期：v.3,no.1(January 4, 2013)
- ISSN：2155-5435
文摘
Porosity is a factor affecting catalyst efficiency in pelletized form. This implies that care should be taken with uncritically relating activity measurements from transmission operando FTIR to final catalyst performance. If the pelletizing pressure is excessive, a destruction of the pore structure of, for example, support oxides might take place, which in turn affects the pore size distribution and the porosity of the catalyst, leading to the observation of lower activity values due to decreased catalyst efficiency. This phenomenon can also apply to conventional activity measurements, in the cases that pelletizing and recrushing of samples are performed to obtain adequate particle size fractions for the catalytic bed. A case study of an operando investigation of a V2O5-WO3/TiO2-sepiolite catalyst is used as an example, and simple calculations of the influence of catalyst activity and internal pore diffusion properties are considered in this paper for the evaluation of catalyst performance in, for example, operando reactors. Thus, it is demonstrated that with a pelletizing pressure of <1鈥? ton/cm2, the pore structure is only negligibly altered, and small deteriorations of estimated catalyst efficiencies are observed for first-order kinetic constants lower than 100 mL/gs. However, if the operando study deals with highly active catalysts, it is necessary to consider efficiency losses. A simple procedure for evaluating efficiencies based on pellet dimensions and solid phase characteristics is proposed. The Thiele modulus is directly proportional to the thickness of the pellet, and, thus, inversely related to the catalyst efficiency. As a rule of thumb, we found that for catalytic constants below 100 mL/gs, the maximum thickness of the pellet pressed at 2 tons/cm2 has to be as low as 80 渭m to exhibit catalyst efficiencies above 90%. For catalysts with k鈥?= 10 mL/gs, the value is 260 渭m. This strongly underlines the importance of taking internal diffusion limitations into account when working with highly active catalysts.