Formation and Fate of Formaldehyde in Methanol‐to‐Hydrocarbon Reaction: In Situ Synchrotron Radiation Photoionization Mass Spectrometry Study

Abstract

HCHO has been confirmed as an active intermediate in the methanol‐to‐hydrocarbon (MTH) reaction, and is critical for interpreting the mechanisms of coke formation. Here, HCHO was detected and quantified during the MTH process over HSAPO‐34 and HZSM‐5 by in situ synchrotron radiation photoionization mass spectrometry. Compared with conventional methods, excellent time‐resolved profiles were obtained to study the formation and fate of HCHO, and other products during the induction, steady‐state reaction, and deactivation periods. Similar formation trends of HCHO and methane, and their close correlation in yields suggest that they are derived from disproportionation of methanol at acidic sites. In the presence of Y2O3, the amount of HCHO changes, affecting the hydrogen‐transfer processes of olefins into aromatics and aromatics into cokes. The yield of HCHO affects the aromatic‐based cycle and the formation of ethylene, indicating that ethylene is mainly formed from the aromatic‐based cycle.

Role of formaldehyde in promoting aromatic selectivity during methanol conversion over gallium-modified zeolites

“…The researchers studied the behavior of HCHO in MTH by adding HCHO into the reactants, and found that the addition of HCHO can significantly increase the selectivity to aromatics 15,20,21 , and accelerate catalyst deactivation 22,23 . In our previous work, the critical role of HCHO in the mechanisms of aromatic formation was confirmed with the excellent time-resolved profiles obtained by in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) 24 .…”

“…In this work, in situ SR-PIMS (Supplementary Fig. 1) was further utilized to explore the formation and function of HCHO in MTH over Ga-modified HZSM-5 24 . To alleviate the secondary reactions of HCHO, a 2 Torr pressure was applied to the catalytic reactor.…”

Assessing the effects of dealumination and bifunctionalization on 8-membered ring zeolite/zeo-type materials in the methanol-to-olefin catalytic process

“…In existing literature, this deactivation phenomenon has often been associated with the detrimental role of formaldehyde (HCHO) or its derived oxymethylene species, which promote the generation of aromatics-based coke precursors and expedite catalyst deactivation. 17,30,52,70,71 HCHO is a by-product in MTO catalysis, resulting from the disproportionation of methanol (2CH 3 OH → CH 4 + HCHO). 30 To mitigate the adverse impact of HCHO, metallic scavengers such as Y 2 O 3 are typically combined with zeolites to form bifunctional catalytic systems, enhancing the reaction's durability.…”

“…In existing literature, this deactivation phenomenon has often been associated with the detrimental role of formaldehyde (HCHO) or its derived oxymethylene species, which promote the generation of aromatics-based coke precursors and expedite catalyst deactivation. 17,30,52,70,71 HCHO is a by-product in MTO catalysis, resulting from the…”