Reactions CO, H2 - synthese du methanol sur chromite de zinc etude d'especes chimisorbees a la surface du catalyseur schemas reactionnels possibles

A New Approach to the Mechanism of Fischer–Tropsch Syntheses Arising from Gas Phase NMR and Mass Spectrometry

“…In af urther experiment, 13 C-labeled iron carbide NPs were reactedw itha1:1H 2 / 12 CO mixture at 210 8Cf or 48 h. NMR spectroscopy of the gas phase showedt he formation of several hydrocarbons ando lefins, as expected for aF TS reaction, but none of these products showed any evidenceo f 13 Ce nrichment (Figure 3a and b). This demonstrates the absence of the incorporation of the carbide carbon atom into the reaction products under these conditions.…”

“…[4] The surfacec arbide mechanism has received support from many groups, [5] and more recently from Niemantsverdriet and co-workers [6] who used DFT calculations to model CO hydrogenation over Fe 5 C 2 .V ery recently, Khodakov et al [7] investigated the role of the carbon atoms of supported 13 C-labeled iron carbide in FTS at 300 8C. They evidenced the incorporation of the carbidec arbon atoms into the reactionp roducts (initialf raction of 13 Ci nC 2 -C 4 :1 0-16 %), but the isotope distribution in the C 2 -C 4 fraction led them to conclude that the carbidem ay play the role of ac hain growth initiator.T he enol mechanism [8] deals with the nondissociative chemisorption of CO that reacts with adsorbed hydrogen to form enolic units.…”

“…They evidenced the incorporation of the carbidec arbon atoms into the reactionp roducts (initialf raction of 13 Ci nC 2 -C 4 :1 0-16 %), but the isotope distribution in the C 2 -C 4 fraction led them to conclude that the carbidem ay play the role of ac hain growth initiator.T he enol mechanism [8] deals with the nondissociative chemisorption of CO that reacts with adsorbed hydrogen to form enolic units. Ac ombination of surface polymerization, condensation, andw ater elimination steps by adjacent groups leads to the formation of hydrocarbons.…”

“…[2d, 10, 11] The CO insertion mechanism, also known as the Pichler-Schulz mechanism, wasi ntroduced later and consists of the insertion of CO into am etalÀalkyl bond that is then hydrogenated to produce alcohols, alkenes, and alkanes. [12] Variants of this mechanism include the insertiono fC Oi nto the OÀHb ond of an adsorbed OH group [13] and even the hydrogenation of CO to lead to oxygen atoms bondedd irectly to the metal surface. [14] We have shown recently that it is possible to transform monodisperse Fe 0 nanoparticles (NPs) into monodisperse iron carbide( FeC x )N Ps by at wo-step procedure.…”

Methanol

“…Until the beginning of the 1980s, mechanistic considerations were based almost exclusively on the hydrogenation of carbon monoxide to methanol (Eq. 1, see 4.1.1) [55][56][57][58][59]. The increased yield achieved by adding carbon dioxide was ascribed to the displacement of the reverse water-gas shift equilibrium (Eq.…”