(569ac) Investigating Metal Poison Deposition Onto Zeolite-Supported Hydropyrolysis Catalysts Via Liquid-Phase Titration of Acid Sites and Infrared-Spectroscopic Analyses

Methods for quantifying acid site density and speciation in zeolites have only recently been extended broadly to the liquid phase. The presumed need to study gas-phase metals disposition into zeolite catalysts under self-consistent laboratory conditions in order to understand their impacts on catalyst deactivation behaviors has therefore limited the pace of fundamental research into this issue, as acid site distributions determined by liquid and gas phase methods cannot necessarily be directly compared. For example, the formation of solvent structures around basic probe ions will alter their effective kinetic diameter vs. in a vacuum. However, liquid phase protocols lend themselves more readily to controlled dosing of metal precursors into support framework than gas phase methods at bench top scales. Accordingly, the ability to reliably compare materials synthesized via gas- vs. liquid-phase metals deposition mechanisms directly represents an opportunity in biomass pyrolysis research, where realistic feedstocks entrain concentrated alkali metals and other catalyst poisons; which are non-volatile and will quickly deposit on the catalyst under gas-phase processing conditions. Here, we report the design and fabrication of an ATR-FTIR-enabled, liquid-phase apparatus for determining the total acid site density within the pores of zeolites, and the speciation of same across IR-distinguishable Brønsted- and Lewis-acidic facets via analysis of extinction coefficients. We demonstrate the utility of this liquid-enabled protocol in qualifying the impact of depositing metals (e.g. K) into HZSM-5 zeolites via liquid precursors (e.g. KNO3) on the acid site density and speciation of the catalysts, and compare these profiles to the amount of metal dopant introduced into the framework (determined by XRF) and the activity of the acid catalyst (reported by GC-MS-determined selectivities of gas-phase ethanol dehydration toward corresponding hydrocarbon products). We demonstrate the ability to recover literature-reported trends in acid catalyst properties and activities versus those modified with metal dopants under gas-phase conditions.