The Dynamic Catalytic Activity of Phosphorus-containing Catalysts

05 December 2023, Version 2


The active site speciation of phosphorus-containing all-silica zeolites, P-zeosils, involves a dynamic distribution that is manipulated through controlled hydrolysis of the catalytic material. While water vapor is known to enhance the catalytic activity of phosphorus-based catalysts through phosphorous linkage hydrolysis, here we demonstrate that hydrolysis using a combination of water and sufficiently basic nitrogen-containing compounds like alkylamines increases the acid site density by more than an order of magnitude relative to water-only hydrolysis. The approach of base-assisted hydrolysis was found to be applicable to multiple catalytic chemistries, facilitating both the rates of alcohol dehydration (300× rate enhancement) and alkylamine Hofmann elimination (15× rate enhancement) over P-zeosils. Through a broad array of in situ and ex situ characterization, the enhancement of catalytic activity via base-facilitated hydrolysis was attributed to enhanced acid site density as a result of shifting the dynamic distribution of P-moieties to less condensed states. Specifically, more recalcitrant P-O-P linkages not cleaved through water only hydrolysis, were readily hydrolyzed in the presence of a base. Sufficient basicity in the nitrogen-containing group is critical to access the highest possible density of acid sites, which greatly exceeds that achievable through hydrolysis alone.


Alcohol Dehydration
Hofmann Elimination
General Base Catalysis
Phosphate Hydrolysis
Solid Phosphoric Acid

Supplementary materials

Supporting Information
Details of the experimental setup, kinetic measurement of 2-propanol dehydration over Al-BEA, activation of P-BEA with only water or only TBA, rate profile during in situ poisoning for site density measurements, rate dependence of TBA Hofmann elimination over Al-MFI and P-BEA, FT-IR spectra, XANES spectra, and elemental analysis result by XPS are available in the supporting information.


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