Model propane oxidation

The present chapter will primarily focus on oxidation reactions over supported vanadia catalysts because of the widespread applications of these interesting catalytic materials.5 6,22 24 Although this article is limited to well-defined supported vanadia catalysts, the supported vanadia catalysts are model catalyst systems that are also representative of other supported metal oxide catalysts employed in oxidation reactions (e.g., Mo, Cr, Re, etc.).25 26 The key chemical probe reaction to be employed in this chapter will be methanol oxidation to formaldehyde, but other oxidation reactions will also be discussed (methane oxidation to formaldehyde, propane oxidation to propylene, butane oxidation to maleic anhydride, CO oxidation to C02, S02 oxidation to S03 and the selective catalytic reduction of NOx with NH3 to N2 and H20). This chapter will combine the molecular structural and reactivity information of well-defined supported vanadia catalysts in order to develop the molecular structure-reactivity relationships for these oxidation catalysts. The molecular structure-reactivity relationships represent the molecular ingredients required for the molecular engineering of supported metal oxide catalysts. 

In contrast, however, the following simple model [176] for propane oxidation, in which propyl hydroperoxide is the agent of degenerate branching, viz. 

The TPD/XPS results indicated that CO, propane and propene bind stronger to a reduced V-terminated 203(000 ) surface than to an oxidized V = 0 terminated surface. Nevertheless, vanadyl groups are probably required in the course of catalytic reactions. However, rates of propane oxidative dehydrogenation (ODH) to propene at atmospheric pressure are rather low and no reaction products were observed by gas chromatography, both for oxidized and reduced V Oj model surfaces at temperatures up to 500 K [12]. 

Below we illustrate [43] the importance of facet-facet communication by analyzing a kinetic model of oxidation of saturated hydrocarbons. As a specific example, we treat propane oxidation,... 

Detailed Modelling of Acetaldehyde or Propane Oxidation.— The second approach, stated at the outset, attempts to choose a complete kinetic mechanism of a specific system and to proceed to a numerical solution of the detailed mass and energy balance equations via a digital computer. This is the approach chosen by Halstead et al. " who have concentrated on the gas-phase oxidations first of acetaldehyde and latterly of propane. " In the acetaldehyde reaction, Halstead et al. identified peracetic acid as the degenerate branching agent and attributed the self-quenching... 

Curran, H. Jayaweera, T. Pitz, W. Westbrook, C. (2004). A Detailed Modeling Study of Propane Oxidation, Proceedings of Western States Section meeting of The Combustion... 

Dagaut P, Cathormet M, Boettner J-C. Kinetic modeling of propane oxidation and pyrolysis. Int J Chem Kinet... 

Petersen EL, Kalitan DM, Simmons S, Bourque G, Curran HJ, Simmie JM. Methane/ propane oxidation at high pressures experimental and detailed chemical kinetic modeling. Proc Combust Inst. 2007 31 447-454. 

The identification and quantification of potentially cytotoxic carbonyl compounds (e.g. aldehydes such as pentanal, hexanal, traw-2-octenal and 4-hydroxy-/mAW-2-nonenal, and ketones such as propan- and hexan-2-ones) also serves as a useful marker of the oxidative deterioration of PUFAs in isolated biological samples and chemical model systems. One method developed utilizes HPLC coupled with spectrophotometric detection and involves precolumn derivatization of peroxidized PUFA-derived aldehydes and alternative carbonyl compounds with 2,4-DNPH followed by separation of the resulting chromophoric 2,4-dinitrophenylhydrazones on a reversed-phase column and spectrophotometric detection at a wavelength of378 nm. This method has a relatively high level of sensitivity, and has been successfully applied to the analysis of such products in rat hepatocytes and rat liver microsomal suspensions stimulated with carbon tetrachloride or ADP-iron complexes (Poli etui., 1985). 

The gas mixture containing the nitrogen oxides is very important as well. Experiments and modeling carried out for N2/NOx mixtures, or with addition of 02, H20, C02 and hydrocarbons will be discussed. Typical hydrocarbon additives investigated are ethane, propene, propane, 2-propene-l-ol, 2-propanol, etc. As compared to the case without hydrocarbons, NO oxidation occurs much faster when hydrocarbons are present. The reaction paths for NO removal change significantly, in fact the chemical mechanism itself is completely different from that of without hydrocarbon additives. Another additive investigated extensively is ammonia, used especially in corona radical shower systems. 

This heme-dependent enzyme [EC 1.11.1.14], also known as diarylpropane peroxidase, diarylpropane oxygenase, and ligninase I, catalyzes the reaction of 1,2-bis(3,4-dimethoxyphenyl)propane-l,3-diol with hydrogen peroxide to produce veratraldehyde, l-(3,4-dimeth-ylphenyl)ethane-l,2-diol, and four water molecules. The enzyme brings about the oxidative cleavage of C—C bonds in a number of model compounds and also oxidizes benzyl alcohols to aldehydes or ketones. 

Adlerol, i.e. l-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxyphenoxy)propan-l-ol, is a well-established dimeric model compound of lignin and, as such, its oxidation to the ketone-derivative Adlerone, i.e. l-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxyphen-oxy)propan-l-one, has been taken as a benchmark reaction (Scheme 20) to evaluate the efficiency of several chemo-enzymatic procedures. 

Table 8.1 shows the stochastic model solution for the petrochemical system. The solution indicated the selection of 22 processes with a slightly different configuration and production capacities from the deterministic case, Table 4.2 in Chapter 4. For example, acetic acid was produced by direct oxidation of n-butylenes instead of the air oxidation of acetaldehyde. Furthermore, ethylene was produced by pyrolysis of ethane instead of steam cracking of ethane-propane (50-50 wt%). These changes, as well as the different production capacities obtained, illustrate the effect of the uncertainty in process yield, raw material and product prices, and lower product... 

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