Tracking the coupling conversion of C1-C4 aldehydes with methanol-to-hydrocarbon reaction

Small-molecule aldehydes are promising additives to regulate product distribution in methanol-to-hydrocarbon (MTH) reaction. Herein, the co-feeding of C-1-C-4 aldehydes with methanol resulted in a significant increase in aromatic formation with the order: acetaldehyde > formaldehyde > propanal approximate to butanal. The mechanistic basis for this enhancement in aromatic production derived from both a direct participation pathway of aldehydes and an indirect pathway via driving the aromatic-based cycle. C2+ aldehydes could undergo multiple aldol-condensation on Br & oslash;nsted acid sites to form larger alkenals, followed by sequential cyclization-dehydration reaction to cycloalkenes or aromatic species. The Prins reaction could be extended to all C-1-C-4 aldehydes with alkenes by generating the corresponding dienes. The hydrogen transfer from methanol to C2+ aldehydes produced C2+ olefins and formaldehyde, which would lead to extra formaldehyde-mediated aromatic formation pathway. The intricate evolution pathway of C-1-C-4 aldehydes in MTH reaction was constructed by detecting abundant oxygenate and hydrocarbon intermediates.