Catalytic Dehydrogenation Of Methanol Research Articles

Mechanistic study on dehydrogenation of methanol with [RuCl 2(PR 3) 3]-type catalyst in homogeneous solutions

Catalytic dehydrogenation of methanol has been investigated in homogeneous solutions with a series of Ru(II) complexes, [RuCl 2(P( p-C 6H 4X) 3) 3] (X = H (1), Me (2), F (3), OMe (4)) and [RuCl 2(PMePh 2) 3] (5). In the gas phase, hydrogen was formed selectively (> 99.5%), and formaldehyde, methylal (formaldehyde dimethyl acetal) and methyl formate were found in the liquid phase with satisfactory stoichiometry to the formed hydrogen. The reaction was retarded by the extra addition of free phosphine, suggesting the presence of pre-equilibrium dissociation of phosphine ligand. Kinetic analyses from this viewpoint explained well the dependence of rate on the concentration of catalyst (saturation curve). The order of evaluated pre-equilibrium constant (1 ≈ 2 > 5) is in accord with the general idea that the dissociation of phosphine ligand is controlled principally by steric bulk of ligands. The order of rate (3 > 1 > 2 > 4) for 1–4, possessing the same cone angle of phosphine ligand, correlated clearly with basicity of phosphines. The results are interpreted in terms of the mechanism of rate-determining β-hydrogen abstraction in the Ru-OCH 3 intermediate.

Studies on Catalytic Dehydrogenation of Methanol to Formaldehyde

Studies on Catalytic Dehydrogenation of Methanol to Formaldehyde

Catalytic dehydrogenation of methanol with ruthenium complexes

Dihydrogen was evolved at sufficiently high reaction rates from the methanol solution of ruthenium chloride under reflux conditions in the presence of an excess of sodium methoxide, with small amounts of sodium hydroxide. An activation energy of 123 kJ mol −1 was obtained for the methanol solution containing sodium methoxide (20 wt.%). At low sodium methoxide concentrations, however, removal of the Cl − ligand from the ruthenium species by adding silver tetrafluoroborate accelerated the reaction. Sodium formate was ascertained to be the reaction product in the solution. The correlation between the coordination structure of ruthenium and the catalytic activity is discussed.

Dehydrogenation of methanol to methyl formate over supported copper catalysts

The catalytic dehydrogenation of methanol over copper-supported (Cu/ MO χ, M=Si, Zr, Mg, Zn and graphite) catalysts has been studied in a fixed bed microreactor in the temperature range of 180–260°C. The copper/silica and copper/zirconium oxide catalysts were found to be very active and selective toward methyl formate (MF) formation. However, the copper/zinc oxide catalyst was less active and the copper/magnesium oxide one much less selective. The exception was the copper/graphite catalyst whose performance approached that of massive copper. The reaction has also been studied on CuM/SiO 2 (M=Na 2O, ZnO, Cr 2O 3) promoted catalysts. Only in the case of copper promotion by 0.1% sodium (copper/sodium=11.2 atomic) was the specific activity found to increase, while the MF selectivity remained unchanged. The state of copper in the catalysts used in the reaction was determined by X-ray photoelectron spectroscopy. With the sole exception of the copper/magnesium oxide catalyst, which was partially oxidised as Cu 2+, the other catalysts showed only reduced copper species. For the used 15.1% copper/silica catalyst the position of the copper L 3VV X-ray induced Auger transition at 913.4 eV confirmed the existence of reduced Cu 0. Additional catalytic experiments carried out on unreduced silica-supported copper catalysts, using carbon dioxide as a carrier feed, showed that a longer time onstream was required before a steady state was achieved, which in turn is typical of catalyst activation by the hydrogen reaction byproduct (eqn. 4). Carbon monoxide poisoning experiments led to the conclusion that metallic copper is very likely the active copper species in this reaction. Furthermore, the infrared spectra of methanol adsorption on the poorly selective 5.7% copper/magnesium oxide catalyst revealed that the MF product undergoes decomposition through carbonate structures at basic sites.

Orientation of CH3O on Cu(110) as examined by near-edge x-ray-absorption fine-structure spectroscopy.

The orientation of the methoxy species (${\mathrm{CH}}_{3}$O) found as an intermediate in the catalytic dehydrogenation of methanol on Cu(110) has been determined by analysis of the near-edge x-ray-absorption fine structure at the oxygen K edge in the azimuths [001] and [11\ifmmode\bar\else\textasciimacron\fi{}0]. In both azimuths the C-O axis is tilted by 36\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}5\ifmmode^\circ\else\textdegree\fi{} with respect to the surface normal.

Dehydrogenation of methanol to formaldehyde over silicalite

Formaldehyde is formed by catalytic dehydrogenation of methanol over silicalite containing sodium ions at 670–820 K.

1132. Catalytic dehydrogenation of methanol over zinc oxide and doped zinc oxide

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