Abstract
The conversion of alcohols towards aldehydes in the presence of catalysts by non-oxidative dehydrogenation requires special importance from the perspective of green chemistry. Sodium (Na) super ionic conductor (NASICON)-type hydrogen titanium phosphate sulfate (HTPS; H1−xTi2(PO4)3−x(SO4)x, x = 0.5–1) catalysts were synthesized by the sol-gel method, characterized by N2 gas sorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), NH3 temperature-programmed desorption (NH3-TPD), ultraviolet–visible (UV-VIS) spectroscopy, and their catalytic properties were studied for the non-oxidative dehydrogenation of methanol and ethanol. The ethanol is more reactive than methanol, with the conversion for ethanol exceeding 95% as compared to methanol, where the conversion has a maximum value at 55%. The selectivity to formaldehyde is almost 100% in methanol conversion, while the selectivity to acetaldehyde decreases from 56% to 43% in ethanol conversion, when the reaction temperature is increased from 250 to 400 °C.
Highlights
Dehydrogenation of alcohols to aldehydes is important for producing the precursors for manufacturing downstream products, including fine chemicals, pharmaceuticals, polymers, and inks
We report NASICON-type hydrogen titanium phosphate sulfate (HTPS; H1−x Ti2 (PO4 )3−x (SO4 )x, x = 0.5–1) as the first metal-free solid acid catalyst that is highly efficient for dehydrogenation of methanol to formaldehyde and for conversion of ethanol to acetaldehyde and ethylene, in the absence of O2
Volume is associated with sulfate loss calcination at 700 °C coincides with an increase in the crystallite size as well as the enlargement of the unit cell volume which is associated with sulfate loss [23]
Summary
Dehydrogenation of alcohols to aldehydes is important for producing the precursors for manufacturing downstream products, including fine chemicals, pharmaceuticals, polymers, and inks. In a thermodynamic consideration of dehydrogenation, conversion of methanol to formaldehyde is 20% at 400 ◦ C and increases to 87% at 600 ◦ C [4] This reaction becomes insignificant when the competing full dehydrogenation to carbon monoxide is included. Catalysts based on transition metals, such as copper, are very active for alcohol dehydrogenation, but the main products are hydrogen and carbon monoxide [5]. Establishing kinetic control by employing catalysts is needed to enhance conversions at low temperatures and to suppress competing reactions. Other side reactions, such as the formation of coke, need to be eliminated [6]
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