Model methanol dehydrogenation

Metal cations Metal cation reduction Metal cations in MeAPO synthesis Metal corrosion prevention Metallocene, supported catalyst 24-0-05 Metallosilicates, microporous Methanol adsorption Methanol amination Methanol conversion Methanol dehydrogenation Methanol formation Methanol in alkylation 15-0-03 25-0-03 Methanol to hydrocarbons Methanol, reagent Methanol, steam reforming Methylamine in MFI synthesis N-Methylation, aniline Methylation, 4-methylbiphenyl Methylation, toluene, model 4-methylbiphenyl, methylation Methylcyclohexane cracking Methylcyclopentane hydroconversion Methylene silanes... 

In this chapter, we provide a succinct review of some of the advances in the development and application of ab initio methods toward understanding the intrinsic reactivity of the metal and the influence of the reactive site and its environment. We draw predominantly from some of our own recent efforts. More specifically we describe (a) the chemistry of the aqueous-phase on transition metal surfaces and its influence on the kinetics and thermodynamics within example reaction mechanisms, and (b) computational models of the electrode interface that are able to account for a referenced and tunable surface potential and the role of the surface potential in controlling electro-catalytic reactions. These properties are discussed in detail for an example reaction of importance to fuel cell electrocatalysis methanol dehydrogenation over platinum(ll 1) interfaces [24,25]. 

The oxidative dehydrogenation of methanol to formaldehyde is a model reaction for performance evaluation of micro reactors (see description in [72]). In the corresponding industrial process, a methanol-air mixture of equimolecular ratio of methanol... 

The oxidative dehydrogenation of methanol to formaldehyde was choosen as model reaction by BASF for performance evaluation of micro reactors [1, 49-51, 108]. In the industrial process a methanol-air mixture of equimolecular ratio of methanol and oxygen is guided through a shallow catalyst bed of silver at 150 °C feed temperature, 600-650 °C exit temperature, atmospheric pressure and a contact time of 10 ms or less. Conversion amounts to 60-70% at a selectivity of about 90%. 

Another model in which bulk effects are suspected was discussed by Dress et al. (177,178) for methanol oxidation on supported Pd catalysts. The authors postulate that an initial dehydrogenation of the methanol to CO and H2 occurs. The dissolves in the Pd lattice until the concentration necessary for the formation of the Pd-H /3 phase is reached. On the jS phase, CO oxidation is assumed to exhibit a higher rate, and CO is thus removed by reaction with oxygen. The H from the Pd bulk is then oxidized until the Pd-H a phase is again formed. The stability of a simplified version of this model was analyzed in the same publications. 

Fig. 8.9 Up) Model of a (a) pure fcc(lll) surface (x = 0), Se-containing surface with (b) small (x = 0.25), (c) moderate (x = 0.50), (d) high (x = 0.75) content in Se, and a fcc(lll) surface covered with a monolayer of Se (x = 1) (Bottom) Change in free energy associated with the initial activation of methanol (UMO) plotted against the ORR activity (UORR). For structures lying on the upper left part of the plot methanol activation is thermodynamically unfavorable, with UMO > UORR. For structures lying on the lower right part such as Pt, methaonol readily dehydrogenates since UMO < UORR (Source [126] reproduced with permission of Elsevier)...

Diakov, V. and Varma, A. (2003). Methanol Oxidative Dehydrogenation in a Packed-Bed Membrane Reactor Yield Optimization Experiments and Model, Chem. Eng. Sci, 58, pp. 801-807. 

According to bifunctional mechanism proposed by Watanabe and Motoo [62], the dehydrogenation of methanol occurs on the Pt active sites as a result of producing CO-like species. The Ru species could decompose water at a lower potential than Pt to produce —OH species, which could react with the CO-like species on Pt active sites and detoxify them. On the premise of this mechanism, the model catalyst should be described as good PtRu alloy (atomic ratio Pt/Ru = 1 1) with the two elements mixing at atomic scale (Figure 10.11). 

Diakov, V., Blackwell, B. and Varma, A. (2002) Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor Experiments and model. Chemical Engineering Science, 57, 1563—1569. 

---