Developing multiple-site kinetic models in catalysis simulation: A case study of O-2+2NO <-> 2NO(2) oxidation-reduction chemistry on Pt(100) catalyst crystal facets

作者：Disselkamp RS^*; Tonkyn RG; Chin YH; Peden CHR

来源：Journal of Catalysis, 2006, 238(1): 1-5.

DOI：10.1016/j.jcat.2005.11.031

• multiple-site kinetic model
• site-specific microkinetic modeling

It is generally recognized that developing a kinetic model for a supported catalyst is difficult because of the existence of multiple sites. These sites can arise from a distribution of crystal facets (e.g., (100), (110)) each with its unique intrinsic site types (e.g., atop, bridge, hollow). Additional complexities arise from non-basel plane site types (e.g., defect, edge, corner), the differing lateral interaction energies of which may be coverage-dependent for each of their pairwise interactions. To demonstrate the complexities that develop for even a greatly simplified system, we examine a multiple site kinetic model of the reaction 2NO + O-2 <-> 2NO(2) on an ideal Pt(100) catalyst. A model of the Pt(100) surface is adopted where atop, bridge, and fourfold hollow sites are responsible for O-2, NO, and NO2 chemisorption to form Pt-O, Pt-NO, and Pt-NO2 species. In our kinetic scheme, equilibrium is assumed for O-2, NO, and NO2 chemisorption due to their high sticking coefficients (all > 0.1). A single rate-determining step of the Langmuir-Hinshelwood type was chosen to describe the oxidation of NO on platinum via the reaction Pt-H,Pt-A,Pt-B-O + Pt-H,Pt-A,Pt-B-NO <-> Pt-H,Pt-A,Pt-B + Pt-H,Pt-A,Pt-B-NO2, where H, A, and B represent hollow, atop, and bridge sites. Equal kinetic parameters for all site combinations were assumed to exist and were in part taken from the literature to be Delta H-dagger = 83 kJ/mol and Delta S-dagger = 20 J/(K mol). The exercise here is largely hypothetical but offers insight into how more detailed kinetic models may be developed, such as through the use of reaction velocity matrices, a concept introduced here. Specifically for this system, the model yielded insight into NOx chemistry on Pt(100) in that it predicted that the greatest reaction velocities (forward and reverse) occurred via the reaction Pt-O(atop) + Pt-NO(bridge) <-> Pt(atop) + Pt-NO2(bridge). We believe that the framework of a site-specific modeling scheme presented here is ail important starting point for future site-specific microkinetic modeling. In particular, a definition and description of use of surface coverages, reaction rate coefficients, and computed reaction velocity matrices are presented.

• 出版日期2006-2-15