Abstract
Gas phase toluene hydrogenation is investigated over Pt/Al2O3 catalyst with temperature ranging from 75 to 125 °C and at atmospheric pressure. Strong activity variations are observed during long duration experiments. These variations are thoroughly investigated and a mechanistic model is proposed with dynamic adsorption activity of the reactants, used to explain the decrease in catalyst activity. This model considers competitive adsorption behaviour of the reactants and dissociative adsorption of hydrogen. Such a model can also be used to explain the strong metal-support interaction (SMSI) effect induced by the catalyst support. The decrease in activity after temperature maxima as previously observed can also be addressed by the approach presented. A comparison of activity variation at different residence times i.e. 20–50 kgcat·s·mol−1 and different hydrogen and toluene partial pressures is also simulated.
Abbreviations
- i :
-
Stoichiometric constant
- j :
-
Stoichiometric constant
- \({\mathbb{C}}\) :
-
Sites on platinum (mol·kgcat −1)
- C :
-
Concentration of species (mol·m−3)
- k :
-
Rate parameters for hydrogenation reaction
- P :
-
Partial pressures (Pa)
- r :
-
Reaction rate
- S :
-
Sites offered by support (mol·kgcat −1)
- T :
-
Temperature (K)
- t :
-
Time (s)
- Tol :
-
Toluene
- α:
-
Hydrogen reaction order
- Γ:
-
Deactivation factor
- *:
-
Species adsorbed on platinum
- s :
-
Species adsorbed on support
- d :
-
Order of deactivation
- ad, H2:
-
Hydrogen adsorption
- ad, Tol:
-
Toluene adsorption
- d, H2:
-
Hydrogen desorption
- d, Tol:
-
Toluene desorption
- H2 :
-
Hydrogen
- Tol :
-
Toluene
- t :
-
Total
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Acknowledgments
We are thankful to Government of Pakistan (Higher Education Commission) for supporting this research work through a doctoral grant to Aqeel Ahmad TAIMOOR.
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Appendix
Appendix
Internal diffusion resistance
Simple mass balance across the pore length yields the following equation
where
let \(t = 0\,\therefore\,\varphi = 1\) so, from empirical model:
Also, from the ideal gas law
By applying boundary conditions, i.e.
and integrating Eq. 17:
where:
- L :
-
= \({\frac{200 \times 10^{-6}}{6}} = 3.33 \times 10^{-5}\,\hbox{m} \)
- W :
-
= 0.002 kgcat
- C t :
-
= 4.33 × 10−2 mol
- k :
-
= \(7.8 \times 10^{-3}\exp\,{{\frac{-21.48}{T}}}\,\hbox{s}^{-1}\,\hbox{kPa}^{-0.6}\)
- \(P_{{\text {H}}_2}\) :
-
= 45585 Pa
- T :
-
= 348 K
- R :
-
= 8.314 J·K−1·mol−1
- V :
-
= 0.003 m3
- \({\cal D}e\) :
-
= \( 5\cdot 10^{-5} {\text{m}^{2}} \cdot{\text{s}^{-1}}\)
\(\triangle\hbox{P}\) is found negligible by calculating from Eq. 17.
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Taimoor, A.A., Pitault, I. Kinetics of toluene hydrogenation—integrating a dynamic approach regarding catalyst activity. Reac Kinet Mech Cat 102, 263–282 (2011). https://doi.org/10.1007/s11144-010-0270-3
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DOI: https://doi.org/10.1007/s11144-010-0270-3