Promoters methanol

Bewick et al." identified CO as the species that acts as a catalytic poison and inhibits further oxidation of methanol on Pt electrodes. The reactive intermediate is a formate species, HCOO that generates asynunetric COO vibration around 1300 cm, leading to an increase in the methanol oxidation current after CO oxidation. "Recently, water molecules were detected adsorbed on the Ru sites on Ru and Pt-Ru (but not on Pt) catalysts, and were assigned as the oxy gen donor to the methanol adsorbates that promote methanol oxidation."" This was considered as directly supporting the bi-functional mechanism of Pt-Ru catalysts for the methanol-oxidation reaction. ... 

Alkali and barium hydroxide promotion of the Cu/ZnO methanol synthesis catalysts has been investigated with the following results (i) at low temperatures, high H2/CO ratios, water-free and C02-free synthesis gas, the alkali promote methanol synthesis rates in the order Cs>Rb>K>Na>Li (ii) the alkali hydroxides are highly dispersed on the catalyst surface (iii) Ba hydroxide agglomerates and shows little effects ... 

There still stands valid for platinum alloys the two metals that are able to promote methanol oxidation are ruthenium and tin. The case of ruthenium is interesting since it was also studied under UHV conditions [43,44]. The reaction of methanol on Pt/Ru alloys results in the production of carbon dioxide at lower potentials than on pure platinum. However, the presence of tin in Pt3Sn alloys only enhances methanol oxidation at low potentials, increasing carbon dioxide production (and diminishing carbon monoxide production) [45]. The addition of tin (II) ions to previously adsorbed methanol produces a fast oxidation process, demonstrated by DEMS experiments [46]. 

Figures Activity in methanol formation at 215°C (conversion selectivity X 10 ) as a function of the relative amounts of extractable Pd " d, Mg promoted total CO conversion o, La promoted total CO conversion , La promoted, methanol formation activity Mg promoted, chlorine free (data from ref. 169)...

A reverse water-gas shift is also promoted over catalysts that promote methanol synthesis and thus must also be considered. This reaction proceeds according to... 

In general, to balance the decomposition of methanol to CO and further oxidation to CO2 requires the consideration of some key factors. In Gasteiger s model [5], it is assumed that methanol oxidation proceeds only via adsorbed CO, and that the dissociative adsorption of methanol is the rate-determining step for methanol oxidation on PtRu electrodes. The electronic effect of Ru on methanol adsorption was not considered. In fact, at low potentials, a low Ru content can promote methanol decomposition to form adsorbed CO, and the oxidation of methanol adsorbates could also control the oxidation of methanol on PtRu electrodes. 

Ru adatoms not only promote methanol oxidation on ft at low potentials but also increase the current efficiency for CO2 generatiOTi. This can be explained by the facts that Ru adatoms can lower the oxidadmi potential of COads on ft, due to the bifunctional mechanism, and that low coverages of Ru adatoms can promote methanol dissociation to form COads on ft at low potentials, resulting from electronic effects. Therefore, Ru adatoms induce a shift from the reaction pathway via soluble intermediates to that via adsorbed CO. At potentials above +0.65 V, the current efficiency for CO2 generation during methanol oxidation on PtRu decreases, since Ru loses its co-catalytic activity at high potentials due to the formation of inactive Ru oxide. 

Abanda-Nkpwatt, D., Miisch, M., Tschiersch, J. et al. (2006) Molecular interaction between Methylobacterium extorquens and seedlings growth promotion, methanol consumption, and localization of the methanol emission site. J. Exp. Botany. 57,4025. 

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