Disquisition on the Acidity in Fluid Catalytic Cracking Catalysts Using Pyridine Probe Molecule Spectroscopy

Abstract

The Fluid Catalytic Cracking (FCC) process has been used for over 75 years to convert crude oil into smaller hydrocarbons like gasoline, propylene and LPG. In this process a FCC catalyst is used composed of zeolite, alumina, silica and clay. Most of the research done on this catalyst focuses on the main active component, zeolite Y. To be able to rationally design the most active, selective and stable FCC catalyst, research on the effect of changes in the binder was done. In the FCC process steam is present, and the effect of steam on the catalysts with different binders is studied. The goal of this work is to make an acidity-activity correlation by studying all of the single components individually as well as combined. Pyridine was used as a probe molecule to determine the acidity of the samples using FT-IR and UV-Vis spectroscopy. Pyridine FT-IR spectroscopy is an established technique to probe acidity as it distinguishes Lewis acid sites (LAS) from Bronsted acid sites (BAS), as well as determines the strength of the acidic sites. While it also provides information on the pyridine adsorbed in a physisorbed manner and pyridine adsorbed on surface hydroxyl groups, it does not give information on the nature of these hydroxyl groups. Recently, pyridine UV-Vis spectroscopy has shown to provide information on the nature of hydroxyl groups present on the surface of solid acids. In this work, pyridine UV-Vis spectroscopy will be used on a full catalyst set for the first time.