Underpinnings of Carbonaceous Deposition among Structurally Diverse Hierarchical Zeolites during Hydrocarbon Upgrading

This work examines how engineered hierarchical (microporous- mesoporous) zeolites influence deactivation during hydrocarbon upgrading. Accumulations of carbonaceous deposits in microporous (MFI, MOR BEA), hierarchical (MFIh, MOR-h, BEA-h), and mesoporous (Al-MCM-41) aluminosilicates at differing crystal size regimes and pore topologies are evaluated as functions of overarching material descriptors like surface areas and pore volumes after liquid-phase, batch alkylation of 1,3,5-trimethylbenzene with benzyl alcohol. Thermogravimetric analysis (TGA) of spent catalysts shows that total foulant accumulation increases linearly with BET surface area (Pearson's r = 0.82), even absent considerations of physical nuances (mesopore connectivity and distribution) or chemical nuances (silanol and proton densities) among diverse hierarchical zeolites prepared by demetalation or recrystallization. Comparing calcination (O2) to pyrolysis (inert) in TGA reveals two foulant classes that preferentially deposit in micropores or mesopores: low organics decomposing at 353-623 K and coke combusting at 623-1073 K. Mass spectrometry of foulants and Raman spectroscopy of catalysts show that low organics are strongly adsorbed reaction species from the alkylation network, while coking involves occlusion of undesired graphitic products of polyalkylation and dehydration. These investigations yield general insights into fouling behaviors of (hierarchical) zeolites having broad synthetic diversity.