Catalyst Particles for Fluid Catalytic Cracking Visualized at the Individual Particle Level by Micro-Spectroscopy

Abstract

In this PhD research the investigation of the reactivity and acidity of Fluid Catalytic Cracking (FCC) catalysts at the level of an individual catalyst particles is described. A range of micro-spectroscopic techniques has been applied to visualize both the active zeolite component within the catalyst particles as well as the matrix components. The most important techniques applied were UV-Vis micro-spectroscopy, confocal fluorescence microscopy, integrated laser and electron microscopy (a combination of fluorescence microscopy and transmission electron microscopy) and synchrotron-based infrared micro-spectroscopy. It was found that the Brønsted acidic zeolite component could be accurately visualized using Brønsted acid catalyzed probe reactions in combination with confocal fluorescence microscopy. The micron-sized zeolite agglomerates were inhomogeneously distributed within the FCC catalyst particles. Laboratory deactivated catalyst particles could be studied with the same approach and their Brønsted acidity, as monitored with confocal fluorescence microscopy, correlated with the cracking activity of the samples. Deactivation of the catalyst particles was observed to occur in a non-preferential manner: external zeolite domains were affected equally compared to more internal zeolite particulates. A sample taken from an industrial FCC reactor showed a large variety in Brønsted acidity among its individual catalyst particles, which accurately reflects the age distribution in such a catalyst batch. The relation between structural features and local Brønsted acidity of individual FCC catalyst particles was investigated in great detail with integrated laser and electron microscopy. Regions in the particles that contained a high amount of zeolite crystals displayed a higher Brønsted acidity than zeolite-poor regions, thus confirming previous results. Structural changes upon deactivation of the catalyst material could be studied at the nanometer scale using the same approach, leading to new insights into the effect of steaming on the zeolite component as well as the matrix material. Furthermore, synchrotron-based infrared micro-spectroscopy after pyridine adsorption was used to study the structure as well as the Brønsted and Lewis acidity of individual FCC catalyst particles in their fresh and deactivated life stages. The decrease in acidity of the FCC catalyst materials upon deactivation could be accurately monitored at the individual particle level using this method. Structural changes in the zeolite and matrix components were apparent from these measurements as well and confirmed the previously obtained insights. Several well-established bulk characterization techniques, among which X-ray powder diffraction, infrared spectroscopy after pyridine adsorption and temperature-programmed desorption of ammonia were used to validate the obtained micro-spectroscopic results. By doing so, the newly developed confocal fluorescence microscopy approach could be benchmarked.