Formation Mechanism of the First Carbon–Carbon Bond and the First Olefin in the Methanol Conversion into Hydrocarbons

Abstract

In dieser Zuschrift wurde fälschlicherweise eine in der Literatur angegebene Reakti-onsgeschwindigkeit als Geschwindigkeitskonstante bei der Geschwindigkeitsberech-nung in den Hintergrundinformationen (S9) verwendet:"As emi-quantitative estimation of the carbonylation rate is made based on reported kinetic data from literature. A rate constant of 6.8 mol (g atom Al) À1 h À1 was applied for the reaction on HZSM-5 at 450 8 8C, according to literature (Fig. 1Angew.C hem. Int. Ed. 2006, 45, 1617-1620). Applying areaction order of 1f or CO and 0f or dimethyl ether,and an H-ZSM-5(Si/Al 90) loading of 1g,acetyl species (HOAc and MeOAc) formation rate of 560 mmol/min under 1mbar CO or 5.6 mmol/min under 0.01 mbar CO was obtained." Eine neue Schätzung der Carbonylierungsgeschwindigkeit durch die Autoren auf der Grundlage ihrer experimentellen Daten ergab, dass diese Aussage korrigiert werden muss zu "A semi-quantitative estimation of the carbonylation rate is made based on our experimental results over H-ZSM-5(Si/Al 90). Acarbon-based reaction rate constant of 140 mmol (g cat) À1 h À1 (bar CO) À1 at 450 8 8Cwas obtained from our DME carbonylation experiment. Applying areaction order of 1f or CO and 0f or dimethyl ether,and an H-ZSM-5 loading of 1g,acetyl species (HOAc and MeOAc) formation rate is calculated to be 140 mmol h À1 (2.3 mmol min À1)under 1mbar CO." Bei 450 8 8Czeigt dieser Katalysator eine Anfangsperionde von ca. 1.5h(g cat) À1 (mol MeOH) À1 vor der Olefindetektion, und er liefert ca. 0.4 %Ausbeute an Methan, was zu einem geschätzten CO-Druck von ca. 0.7 mbar führt. Daraus resultiert eine Ausbeute von 150 ppm Acetylspezies während dieser Anfangsperiode, was sich im DME-Carbonylierungsexperiment als ausreichend zur Initiierung der Olefinbildung selbst bei 300 8 8Cerwies. Die Korrektur der Rechnung ändert daher nichts an der Feststellung eines langsamen Carbonylierungsprozesses und der ausreichenden Anreicherung von Acetylprodukten zur Initiierung der Kohlenwasserstoffbildung. Die Autoren danken Prof. Aditya Bhan, University of Minnesota, fürhilfreiche Kommentare.

Transient kinetic studies and microkinetic modeling of primary olefin formation from dimethyl ether over ZSM‐5 catalysts

“…Recently, we observed that higher temperatures are required to desorb DME in comparison to methanol providing evidence that DME stays longer on the catalysts and is the key oxygenate. This was also evidenced by Liu et al and Wei et al . In this paper, we investigate the induction period during the formation of primary olefins from DME at 300°C by conducting novel step response experiments in a temporal analysis of products (TAP) reactor.…”

“…Various direct mechanisms have been proposed for the conversion of methanol/DME to primary olefins . These direct mechanisms are known by their intermediates and include oxonium ylide, carbene, methane‐formaldehyde, carbon monoxide, methoxymethyl, and surface methoxy groups . Using density functional theory (DFT) calculations, Lesthaeghe et al refuted some direct mechanisms based on high activation energy barriers and highly unstable intermediates.…”

“…Recently, there has been a surge in the evidence for the direct mechanisms leading to primary olefin formation . Li et al gave evidence, using DFT calculations for the formation of propylene from methanol through methoxymethyl cations.…”

“…Nonetheless, the methoxymethyl pathway was more kinetically and thermodynamically favorable. Liu et al, Chowdhury et al, and Plessow and Studt provided spectroscopic and theoretical evidence for a carbon monoxide mechanism. The formation of the first C–C bond (surface acetate group) was shown to involve a low activation barrier of 80 kJ mol −1 .…”

“…In this paper, we investigate the induction period during the formation of primary olefins from DME at 300°C by conducting novel step response experiments in a temporal analysis of products (TAP) reactor. Nine reaction schemes obtained from the literature were compared and used as a basis for a microkinetic model. The experimental data were simulated to extract kinetic parameters that describe the formation of primary olefins from DME over fresh ZSM‐5 catalysts.…”