Abstract
Extension and clustering of polycyclic aromatic hydrocarbons (PAHs) are key mechanistic steps for coking and deactivation in catalysis reactions. However, no unambiguous mechanistic picture exists on molecule-resolved PAHs speciation and evolution, due to the immense experimental challenges in deciphering the complex PAHs structures. Herein, we report an effective strategy through integrating a high resolution MALDI FT-ICR mass spectrometry with isotope labeling technique. With this strategy, a complete route for aromatic hydrocarbon evolution is unveiled for SAPO-34-catalyzed, industrially relevant methanol-to-olefins (MTO) as a model reaction. Notable is the elucidation of an unusual, previously unrecognized mechanistic step: cage-passing growth forming cross-linked multi-core PAHs with graphene-like structure. This mechanistic concept proves general on other cage-based molecule sieves. This preliminary work would provide a versatile means to decipher the key mechanistic step of molecular mass growth for PAHs involved in catalysis and combustion chemistry.
Highlights
Extension and clustering of polycyclic aromatic hydrocarbons (PAHs) are key mechanistic steps for coking and deactivation in catalysis reactions
The dominating deactivating species for SAPO-34-catalyzed MTO reaction evolve from adamantanes at around 270–300 °C28,29, to methylated naphthalene at around 300–450 °C, and to more condensed PAHs when temperature is above 450 °C30
We have demonstrated, through coupling the state-ofthe-art MALDI FT-ICR mass spectrometry (MS) with isotope labeling technique, the cage-passing growth concept by identifying the structural fingerprints of PAHs in an exemplary, industrially important SAPO-34-catalyzed methanol conversion reaction
Summary
Extension and clustering of polycyclic aromatic hydrocarbons (PAHs) are key mechanistic steps for coking and deactivation in catalysis reactions. The formation of PAHs is inevitable in catalysis processes, especially in industrially important petrochemical processes (catalytic cracking, isomerization, transalkylation of aromatics, etc.) and coal-based chemical processes (such as methanol-toolefins (MTO) and syngas conversion) The deposition of these extended aromatic hydrocarbons detrimentally induce catalyst coking and deactivation, necessitating regeneration operations, and posing challenges to practical process design. With the help of two advanced microscopic techniques: confocal fluorescence microscopy (CFM)[10,15] and atom probe tomography (APT)[16,17,18], they visualized the spatial distribution of coke deposits at sub-μm or sub-nm scale in a single catalyst particle, and identified the affinity between the acid sites (enriching on the nearsurface region of catalysts) and the coke clusters (located in the same region)[16,17] These microscopic techniques can unprecedentedly provide effective information on the spatial distribution of coke molecules. They are, still unable to provide molecular fingerprints of those clustered PAHs
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