Promoting effect of active carbons on methanol dehydrogenation on sodium carbonate: hydrogen spillover

Abstract

Methanol dehydrogenation to formaldehyde was conducted in a fixed-bed flow reactor with sodium carbonate catalyst mixed with active carbons or transition metals. The additives promoted the reaction rate at 880-970 K without modifying formaldehyde selectivity. This effect increases with increasing carbon content in the carbon-carbonate mixture. Activation energy of methanol conversion is the same for the mixture and the carbonate alone. Temperature-programmed desorption experiments showed that hydrogen adsorption resulting from dissociative methanol chemisorption was enhanced by adding active carbon to the carbonate. Also, the carbon facilitates hydrogen desorption in comparison to the carbonate. It is suggested that atomic hydrogen produced on sodium carbonate during methanol dehydrogenation spills over onto active carbons (or metals) and recombines to form hydrogen gas. Hydrogen desorption from sodium carbonate, the rate-determining step, is thus accelerated.

Catalytic dehydrogenation of methanol to water‐free formaldehyde

“…As shown in Table2 (Nos3-5), the activity of the carbonate is largely enhanced on mixing with large-surface area active carbons or transition metals (iron or nickel) [46]. This is probably due to hydrogen spillover from the carbonate to the carbons (or metals), which accelerates the rate-determining step.…”

A Comparative Ab Initio Study of Anhydrous Dehydrogenation of Linear-Chain Alcohols on Cu(110)

“…Aldehydes, especially formaldehyde (CH 2 O), with millions of tons produced per year, are key precursors to many important chemical compounds. Currently, formaldehyde is manufactured by oxidative dehydrogenation of methanol (CH 3 OH) using silver-based catalysts, with water as a byproduct: 2 CH 3 OH + O 2 → 2 CH 2 O + 2 H 2 O. − It is desirable to dehydrogenate methanol to formaldehyde in an anhydrous manner, CH 3 OH → CH 2 O + H 2 , that is, without production of water, at moderate temperatures over nonprecious metals, such as Cu or Ni, so that the high energy-cost process of formaldehyde/water separation can be eliminated, − with the H 2 byproduct being useful as a clean fuel. Copper catalyzes anhydrous acetaldehyde (CH 3 CHO) production from ethanol (CH 3 CH 2 OH) at around 200–300 °C, − while the production of formaldehyde from methanol requires either the addition of a promoter (preadsorption of oxygen or water) or extremely high reaction temperatures. ,,, Given that methanol and ethanol, which differ by only one carbon atom in the carbon skeleton, are the two simplest alcohols, it is important to explain the mechanisms responsible for their very different dehydrogenation behavior over Cu.…”

Techno-economic assessment and carbon footprint of processes for the large-scale production of oxymethylene dimethyl ethers from carbon dioxide and hydrogen

“…7), this route was investigated since 1960 to identify selective catalysts for the anhydrous FA synthesis. 61 The lack of direct application of the highly reactive monomeric FA product hinders the market establishment of this production route. In the case of OME synthesis, this valuable monomeric FA product is important, and this route is considered the "dream reaction".…”

“…There is no commercial anhydrous FA synthesis based on the endothermic dissociation of MeOH to monomeric FA and valuable H 2 (eqn (7)), although this route has been investigated since 1960 to identify selective catalysts for the anhydrous synthesis of FA. 61 The lack of direct application of the highly reactive monomeric FA product hinders the market establishment of this production route. In the case of OME synthesis, this valuable monomeric FA product is important, and thus this subprocess is considered the "dream reaction" for the OME value chain.…”