Catalyst modeling

The tltanla-based thin film catalyst models were constructed by first oxidizing the titanium surface In 5 x 10 torr of O2 for approximately 30 minutes at 775 K. This produced an AES llneshape consistent with fully oxidized TIO2. The metal was then vapor deposited onto the oxide support with the latter held at 130 K. The thickness of the metal overlayer and Its cleanliness were verified by AES. After various annealing and adsorption procedures, these thin films were further characterized using SSIMS, AES and TDS. For comparison, some work was done with Pt on Al20s. In this case a Mo foil covered with AI2O3 replaced the Tl(OOOl) substrate. 

Colmenares L, Wang H, Jusys Z, Jiang L, Yan S, Sun GQ, Behm RJ. 2006. Ethanol oxidation on novel, carbon supported Pt alloy catalysts— Model studies under defined diffusion conditions. Electrochim Acta 52 221-233. 

Catalyst Model Compound Model Compound to Glucose Ratio (mole ratio) Glucose Conversion (mol%) HMF Yield (mol%) Other ( mol%)... 

Abstract A three-function catalyst model for hydrocarbon SCR of NOx is described, based on experimental evidence for each function, during temperature-programmed surface reactions (TPSR). 

The single catalyst models for initial NO storage/reduction were then extended to include the catalyst composition, as shown by Eqns (5), (6) and (7). This general model included the nominal weight loadings of Pt, Ba, and Fe, in addition to the five reaction... 

Figure 11.10. Single catalyst model predictions versus experimental initial NO storage/reduction results for catalyst 0.5Pt/7.5Ba/2.5Fe 4 for a) Training data set b) Validation data set for batch 2.

Concept A theozyme ( theoretical enzyme") is a theoretical catalyst model consisting of an array of functional groups optimized so as to maximize stabilization of a transition state (see cartoon below). Theozymes... 

Fully metalated silsesquioxane derivatives of the type Cy7Si709(0M)3 (M = Li, Na, K) would constitute highly desirable precursors for the construction of realistic catalyst model compounds, including novel heterobimetallic species. However, such alkali metal derivatives of 2-7 were unknown until recently, and structural information on such materials was lacking. There have also been contrasting reports in the literature concerning the metalation of 3 by alkali metal... 

The model was validated against heavy duty and passenger car diesel engine test bench experiments. A good correlation was obtained between ESC and ETC experiments and simulation with 0 and 0.5% NO2 NO ratios and a virtual oxidation catalyst. The virtual oxidation catalyst model was realized by placing an oxidation catalyst model in front of the SCR catalyst. 

Wolf-Dieter Deckwer was working along this line and performed experimental investigations to characterise bubble column reactors without and with suspended catalysts, modelled transport processes and chemical reactions in them. 

The studies of well defined systems consists of spectroscopic studies of individual molecules and measurements of the rate of catalytic reactions on single crystal surfaces, as well as structure and reactivity of well-defined catalyst models. 

The structure. The catalyst consists of small particles stabilized by a structural promoter. This challenge may be overcome by studies of suitable catalyst models... 

Pure surfaces to be used as catalyst models may be prepared in a number of ways ... 

The model provides a performance reference to evaluate commercial reformer operation by taking into account the wide variation in operating conditions, feedstocks, and product octane typically experienced commercially. Such variations in reformate yield have already been discussed in Fig. 29, where the model effectively predicts the yield variations. As a monitoring tool, the model is routinely used to assess reformer yield and activity losses due to catalyst deactivation relative to fresh catalyst model estimates. When commercial yield and/or activity losses relative to the model are uneconomical, a decision to regenerate the catalyst is made. A typical monitoring trend (Fig. 36) illustrates the use of the model as a performance reference. 

They focus on the ID simulation of an urea SCR system. The system includes a model for N02 production on a DOC, a model for urea injection, urea decomposition and hydrolysis catalyst, a model for a vanadium-type SCR catalyst and a model for NH3 decomposition on a clean-up catalyst. The catalyst models consist of a ID monolith model with global kinetic reactions on the washcoat surface, kinetic parameters have been taken from literature or adjusted to experimental data from literature. The complete model was implemented in AVL BOOST (2006). AVL BOOST is an engine cycle and gas exchange simulation software tool, which allows for the building of a model of the entire engine. 

The global rate law considering the reaction equilibrium constant is employed quite often in automotive exhaust catalyst models because it ensures the following thermodynamic limitations in a wide range of operating conditions ... 

The different catalyst models within the simulation environment ExACT are used for the simulation of combined aftertreatment systems, when exhaust conditions for a catalyst are influenced by its upstream component and changes in one catalyst affect all components further down the line. An application example is given in the following section and in Chatterjee et al. (2006). It investigates a combined system of DOC and SCR catalyst. Further examples for such combined systems to be investigated are DOC and NSRC or combinations of different catalyst technologies with DPF. 

Li and Balbuena conducted a study of the first electron transfer step (Eq. 47) using the DFT method with a catalyst model of five Pt atoms.105... 

Catalyst models (hypotheses) consist of sets of abstract chemical features arranged at certain positions in the three-dimensional space. The feature definitions are designed to cover different types of interactions between ligand and target, e.g. hydrophobic, H-bond donor, H-bond acceptor, positive ionizable, negative ionizable. Except in some special cases, different chemical groups that lead to the same type of interaction, and thus to the same type of biological effect,... 

Cundari, T.R., Deng, J., Pop, H.F. and Sarbu, C. (2000) Structural analysis of transition metal beta-X substituent interactions. Toward the use of soft computing methods for catalyst modelling. J. Chem. Inf. Comp. Sci., 40, 1052. 

Catalysts, Models of Active Sites and the Polymerisation Mechanism... 

---