2 research outputs found
Acceptorless Dehydrogenative Coupling of Neat Alcohols Using Group VI Sulfide Catalysts
Group VI sulfides
were synthesized via coprecipitation of elemental
sulfur and metal hexacarbonyl and characterized with XRD, XPS, and
TEM. These materials were then demonstrated as active catalysts for
the acceptorless dehydrogenative coupling of neat ethanol to ethyl
acetate, rapidly reaching equilibrium conversion and up to 90% selectivity.
Other primary alcohols form the corresponding esters, while diols
formed the corresponding cyclic ethers and oligomers
Origins of Unusual Alcohol Selectivities over Mixed MgAl Oxide-Supported K/MoS<sub>2</sub> Catalysts for Higher Alcohol Synthesis from Syngas
A series
of MoS<sub>2</sub> catalysts supported on Mg/Al hydrotalcite-derived
mixed-metal oxide (MMO) supports promoted with K<sub>2</sub>CO<sub>3</sub> is used for alcohol synthesis via CO hydrogenation. Alcohol
selectivities are found to vary greatly when the Mo is loaded on the
support at 5 wt % compared with 15 wt % Mo samples, all with a Mo/K
atomic ratio of 1:1. The most striking difference between the catalysts
is the comparatively low methanol and high C<sub>3+</sub> alcohol
selectivities and productivities achieved with the 5% Mo catalyst.
This catalyst also produces more ethane than the 15% Mo catalyst,
which is shown to be associated with ethanol dehydration and hydrogenation
over residual acid sites on this catalyst with lower K content. A
series of catalysts with common composition (5% Mo and 3% K supported
on MMO) prepared in different manners all yield similar catalytic
selectivities, thus showing that selectivity is predominately controlled
by the MMO-to-Mo ratio rather than the synthesis method. When the
Mo loading is the same, catalytic higher alcohol productivity shows some correlation to the degree of stacking of the MoS<sub>2</sub> layers,
as assessed via X-ray diffraction and scanning transmission electron
microscopy. Control reactions in which K loading is increased or the
positioning of the MMO in the catalyst bed is changed via creation
of multiple or mixed catalyst beds show that Mo/K/MMO domains play
a significant role in alcohol-forming reactions. Higher alcohol-forming
pathways are proposed to occur via CO insertion pathways or via coupling
of adsorbed reaction intermediates at or near MoS<sub>2</sub> domains.
No evidence is observed for significant alcohol-coupling pathways
by adsorption of alcohols over downstream, bare MMO supports. Nitrogen physisorption,
XRD, Raman, UV–vis DRS, STEM, and XANES are used to characterize
the catalysts, demonstrating that the degree of stacking of the MoS<sub>2</sub> domains differs significantly between the low (5% Mo) and
high (15% Mo) loading catalysts