Author:

Keywords:

Science & Technology, Physical Sciences, Technology, Chemistry, Physical, Materials Science, Multidisciplinary, Chemistry, Materials Science, STRUCTURE-DIRECTING AGENTS, FRAMEWORK-AL DISTRIBUTION, CHABAZITE ZEOLITES, ALUMINOSILICATE ZEOLITES, SILICA-ALUMINA, SI/AL RATIO, METHANOL, CRYSTALLIZATION, OLEFINS, CHEMISTRY, G0C1618N#54518325, G085220N#55518315, 12ZQ420N#55267580, 1260321N#55921202, 03 Chemical Sciences, 09 Engineering, Materials, 34 Chemical sciences, 40 Engineering

Abstract:

The performance of zeolite catalysts depends not only on the strength and number of Brønsted acid (or exchange) sites but also on synergistic effects derived from their proximity, in particular, and their distribution, in general. Little is known on the genesis of acid sites and site distributions in hydrothermal zeolite synthesis. By an extensive study of five crystallization systems yielding ZSM-5 (MFI) and SSZ-13 (CHA), with a focus on interzeolite conversion (IZC) methods, several synthesis factors and mechanisms that are key in determining the output acid site distribution have been identified. Key in this study were temporal synthesis profiles while probing the distribution and evolution of proximal acid sites with divalent cation capacity measurements. Over the course of different crystallizations, changing local charge distributions are detected, notably within crystalline materials upon prolonged exposure (maturation). Aluminum is clearly the key driver in IZC syntheses, from charge, dissolution, concentration, and mobility points of view. Quasigeneric principles for IZC syntheses are proposed, distinguishing between Al-loving and Al-averse systems, enabling a new degree of control over the acidity and ion-exchange properties of zeolites, of use to tailoring catalytic activity.