Lewis Acidity in Cracking and Polymerization Catalysis

Abstract

The aim of this PhD thesis was to provide insight into the nature and variety of Lewis acidity in solid acid catalysts and to clarify the role of Lewis acid sites in fluid catalytic cracking (FCC) and metallocene-based olefin polymerization catalysis. The definition of an acid site, according to Gilbert Lewis, is an electron pair acceptor.[1–5] A category within the definition of Lewis acidity is the Brønsted acid site (as defined by Johannes Brønsted and Thomas Lowry), which is a molecule capable of donating a proton.[6–8] Cracking and polymerization catalysis by solid acids belong to the pillars of the chemical industry. [9] The fundamental understanding of the chemical nature of their active acid sites is a key parameter for the rational design of these catalysts, which will result in enhanced catalytic performance. An essential part in the investigation into the nature and variety of Lewis acidity in solid catalysts comprised the exploitation of the heterogeneous catalyst characterization toolbox. This PhD thesis has employed a wide range of available state-of-the-art laboratory characterization techniques, including, but not limited to infrared spectroscopy, electronic spectroscopy, optical microscopy, and electron microscopy. A specific category within the characterization toolbox involves the use of probe molecules, whose interaction with acid sites can be studied with spectroscopy. A common thread running throughout this PhD thesis was the necessity to combine multiple characterization techniques at different length-scales, while often pushing the boundaries of what these techniques have to offer in order to achieve insights into the nature and variety of Lewis acidity in solid acid catalysts.