Aromatic aldehydes as tuneable and ppm level potent promoters for zeolite catalysed methanol dehydration to DME

Abstract

Dimethyl ether (DME) is a valuable chemical intermediate and renewable fuel that can be made, via methanol, from many sources of carbon, including carbon dioxide and biomass. Benzaldehyde and its...

Molecular Tuning of Reactivity of Zeolite Protons in HZSM-5

“…Esters are prone to undergo methanolysis and hydrolysis . Although when cofed with methanol, esters and aldehydes promote zeolite-catalyzed methanol dehydration, , their reaction with methanol makes it difficult to clearly delineate effects on the zeolite proton. For example, aromatic aldehydes are shown recently to promote the methanol dehydration reaction by reacting with a protonated methanol to form a transient reactive methyl oxonium species, which directly reacts with another methanol via a S N 2 mechanism to give DME and regenerate the aldehyde promoter .…”

“…Although when cofed with methanol, esters and aldehydes promote zeolite-catalyzed methanol dehydration, , their reaction with methanol makes it difficult to clearly delineate effects on the zeolite proton. For example, aromatic aldehydes are shown recently to promote the methanol dehydration reaction by reacting with a protonated methanol to form a transient reactive methyl oxonium species, which directly reacts with another methanol via a S N 2 mechanism to give DME and regenerate the aldehyde promoter . Because of their direct participation in the reaction, such promotors are reaction-specific and may not be applicable as a general strategy for tuning the reactivity of a zeolite proton.…”

The Oxygenate-Mediated Conversion of COxto Hydrocarbons─On the Role of Zeolites in Tandem Catalysis

“…(1) Catalyst optimization: A wealth of zeolite/zeotype structures, compositions, and BAS/LAS siting are yet to be explored for the tandem reaction. Inspiration for catalyst design may be found from prior studies cited herein. Catalyst morphology may be altered to facilitate product diffusion. Rapid/selective DME or C 2 formation before the zeolite/zeotype function may accelerate hydrocarbons formation in the zeolite/zeotype compared to methanol-mediated routes and mitigate catalyst deactivation, and should be further explored. Long-term catalyst performance, in particular the effect of repeated activation-reaction-regeneration cycles, is underexplored and needs further attention. Potential element migration within and between catalyst functions during synthesis, activation, testing, and regeneration calls for advanced catalyst characterization studies before, during, and after test cycles. Organo-catalysis by guest species in zeolite/zeotype pores and cavities (beyond conventional reaction intermediates and products) may promote desired reactions …”

“…Organo-catalysis by guest species in zeolite/zeotype pores and cavities (beyond conventional reaction intermediates and products) may promote desired reactions …”

Multilevel quantum mechanical calculations show the role of promoter molecules in the dehydration of methanol to dimethyl ether in H-ZSM-5

“…1) can act as potent promoters for the low-temperature (110–150 °C) dehydration of methanol to DME. Preliminary kinetic and spectroscopic studies suggest a mechanism in which the promoters react with methanol to form DME via an associative mechanism, 30,32,33 except possibly for methyl formate which partially dissociates into formic acid and a surface methoxy species. 32 FT-IR studies show that these promoters rapidly adsorb at BASs through the carbonyl group, binding more strongly than methanol; 32 while both species are adsorbed to the BAS through hydrogen bonds, the promoters are further stabilised by van der Waals interactions with the pore walls.…”