Detailed Modelling of Heterogeneous Chemistry on Palladium and Platinum
Author(s)
Bonanni, Michele
Type
Thesis
Abstract
The investigation presents the development, analysis and iterative validation of a heterogeneous
chemical kinetic model for the simulation of reactive hydrocarbon flows over noble metal
catalysts. An axisymmetric, two-dimensional boundary layer system is used to model a virtual
pore, physically and chemically representative of the average pore through a catalytic bed in
short contact time reactors.
A mechanism for the modeling of heterogeneous chemistry over palladium was developed by
adopting the Unity Bond Index Quadratic Exponential Potential (UBI-QEP) for the calculation
of the energetics. This was integrated, where appropriate, with results from ab initio and
experimental investigations. The surface mechanism was coupled with a thoroughly validated
homogeneous gas mechanism to model the oxidative dehydrogenation of ethane over an alumina
supported palladium catalyst (1%Pd/Al2O3).
A bimetallic palladium-platinum mechanism was constructed by coupling the palladium chemistry
with a platinum mechanism previously developed with the same methodology. The refinement of the mechanism was carried out and validated with experimental measurements
of ethane and ethane-acetylene co-feeds over two catalysts (0.2%Pd 3%Pt/Al2O3 and 1%Pd
3%Pt/Al2O3).
Extensive investigation of the sensitivity of the model to physical and chemical parameters was
undertaken and evaluated in concert with the analysis of modifications to the energetics and
chemical kinetic mechanisms. Of particular significance, for the palladium mechanism, was
the reduction of the atomic heat of adsorption of carbon on palladium (to 363 kJ/mol). On
platinum, evidence of poisoning by acetylene confirmed the indication that an increase in the
adsorption energy of acetylene (to 219 kJ/mol) would correct the balance in relative heats of
adsorption of key species.
The study provides a framework for the construction and development of bimetallic heterogeneous
chemical kinetic mechanisms and produces a validated working model for the simulation
of reacting flows over pure palladium and bimetallic palladium-platinum catalysts in a range
of conditions.
chemical kinetic model for the simulation of reactive hydrocarbon flows over noble metal
catalysts. An axisymmetric, two-dimensional boundary layer system is used to model a virtual
pore, physically and chemically representative of the average pore through a catalytic bed in
short contact time reactors.
A mechanism for the modeling of heterogeneous chemistry over palladium was developed by
adopting the Unity Bond Index Quadratic Exponential Potential (UBI-QEP) for the calculation
of the energetics. This was integrated, where appropriate, with results from ab initio and
experimental investigations. The surface mechanism was coupled with a thoroughly validated
homogeneous gas mechanism to model the oxidative dehydrogenation of ethane over an alumina
supported palladium catalyst (1%Pd/Al2O3).
A bimetallic palladium-platinum mechanism was constructed by coupling the palladium chemistry
with a platinum mechanism previously developed with the same methodology. The refinement of the mechanism was carried out and validated with experimental measurements
of ethane and ethane-acetylene co-feeds over two catalysts (0.2%Pd 3%Pt/Al2O3 and 1%Pd
3%Pt/Al2O3).
Extensive investigation of the sensitivity of the model to physical and chemical parameters was
undertaken and evaluated in concert with the analysis of modifications to the energetics and
chemical kinetic mechanisms. Of particular significance, for the palladium mechanism, was
the reduction of the atomic heat of adsorption of carbon on palladium (to 363 kJ/mol). On
platinum, evidence of poisoning by acetylene confirmed the indication that an increase in the
adsorption energy of acetylene (to 219 kJ/mol) would correct the balance in relative heats of
adsorption of key species.
The study provides a framework for the construction and development of bimetallic heterogeneous
chemical kinetic mechanisms and produces a validated working model for the simulation
of reacting flows over pure palladium and bimetallic palladium-platinum catalysts in a range
of conditions.
Date Issued
2011-09
Date Awarded
2012-04
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Lindstedt, Peter
Sponsor
INEOS Technology Limited
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)