Tutorials Manual
Tutorials Manual
Tutorials Manual
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Chemkin 4.1.1<br />
Chapter 3: Catalytic Processes<br />
3.3 Chemistry Sets<br />
In this section, we discuss briefly the chemistry sets used in Chapter 3 and provide<br />
references for further study.<br />
3.3.1 Methane Oxidation on Pt<br />
Two projects in this chapter involve methane oxidation on a platinum surface. This<br />
demonstrates that the gas-phase mechanism does not need to align to a particular<br />
surface mechanism by implementing two different surface mechanisms to describe<br />
the same surface process – methane oxidation on a platinum (Pt) surface.<br />
The chemistry set of the two-stage catalytic combustor project (Section 3.1.1) uses a<br />
slightly altered version of the surface mechanism published by Deutschmann et al. 28<br />
(see p. 93)<br />
in 1996 and put into CHEMKIN format by L. Raja. A different surface<br />
mechanism developed by Chou et al. 30 (see p. 109) in 2000 is employed by the<br />
Parameter Study Facility for the surface chemistry analysis project (Section 3.2.1).<br />
If gas-phase reactions are expected to be important, any reaction mechanism<br />
describing the gas-phase kinetics for methane oxidation chemistry can be used, but<br />
Pt needs to be added to the element list. In both projects, an altered version of the<br />
GRImech 3.0 is provided as an example. In the case of a simulation where it is known<br />
that gas-phase chemistry is not important, a simple gas-phase chemistry input file can<br />
be used that only defines the elements and species that are included in the SURFACE<br />
KINETICS input file.<br />
The SURFACE KINETICS input file for Duetschmann's mechanism describes chemistry<br />
occurring on one material called CATALYST that has one site type called PT_SURFACE.<br />
The PT(B) bulk material is defined, but does not participate in any reactions, as<br />
neither etching or deposition of platinum occurs in this system. The surface site can<br />
be occupied by any of 11 surface species, where PT(S) is the open platinum site, and<br />
the other surface species represent H, C or O atoms, CO, CO 2 or H 2 O molecules,<br />
OH, CH 3 , CH 2 , or CH radicals adsorbed on the platinum surface atom. Note that<br />
GRImech has already used the symbol CH 2 (S) to represent gas-phase methylene<br />
radicals in the singlet electronic state, such that adsorbed methylene radicals have<br />
been given the symbol CH 2 (S)s. Thermochemical data for surface species are<br />
included in the surface kinetics input file, and have been defined using PT(S) as the<br />
reference point. There are 22 surface reactions, some reversible and some<br />
irreversible. These reactions include simple and dissociative adsorption reactions, as<br />
© 2007 Reaction Design 112 RD0411-C20-000-001
Change language