From powder to technical body: the undervalued science of catalyst scale up

Abstract

Progress in catalysis has been, is, and will always be motivated by societal needs (e.g. environment, energy, chemicals, fuels), with the ultimate aim of improving process efficiency on a technical scale. Technical catalysts are often complex multicomponent millimetre-sized bodies consisting of active phases, supports, and numerous additives in shaped forms suitable for their commercial application. They can differ strongly in composition, structure, porosity, and performance from research catalysts, i.e. laboratory-developed materials constituted by a single bulk or supported active phase in powder form, which are the predominant focus of academic investigations. The industrial manufacture of heterogeneous catalysts, encompassing the upscaled preparation, formulation, and structuring, is encircled by secrecy and is decisive for the overall process viability. Yet despite the tremendous relevance, understanding the added complexity of these multicomponent systems and the consequences for the respective structure-property-function relationships has been largely neglected. Accordingly, our review examines the intricacies of the scale up of heterogeneous catalysts. While emphasising the lack of fundamental knowledge we point out the multiple functions that additives could provide by enhancing the mass and heat transfer properties, acting as co-catalysts, or imparting improved chemical, mechanical, or thermal stability. Recent exemplary studies developing rational approaches to prepare, characterise, and evaluate technical catalysts are analysed in detail and new directions for research in this field are put forward.

Binder Effects in SiO2‐ and Al2O3‐Bound Zeolite ZSM‐5‐Based Extrudates as Studied by Microspectroscopy

“…Unlike bulk or supported active‐phase catalysts predominately used in academic research, industrial catalysts involve complex physical and chemical interactions between two or more component phases. The choice of binder(s), combined with the formulation method, can severely impact the material’s catalytic properties 12. The role of the selected binder is particularly lacking in understanding and is often incorrectly labelled “inert”.…”

“…One of the main contributions to the lack of academic interest in zeolite‐based catalyst bodies is the inability to study in detail these large‐scale materials with high enough spatiotemporal resolution, owing to the reduced field‐of‐view required and the lack of suitable characterisation techniques available 12. 20, 21 Given the recent enhancements in chemical imaging methods,22, 23 such as single‐molecule and confocal fluorescence microscopy,21, 24–27 UV/Vis microspectroscopy,28, 29 IR and Raman microscopy,30–32 transmission soft and hard X‐ray microscopy,33–36 X‐ray diffraction computed tomography37 and focused‐ion‐beam scanning electron microscopy,38 coupled with the improved control of these commercial catalysts for modern‐day processes,39 the time is ripe for a shift in academic focus towards understanding these more complex multi‐component and hierarchically structured catalyst materials.…”

Relating structure and composition with accessibility of a single catalyst particle using correlative 3-dimensional micro-spectroscopy

“…The FCC catalyst is designed as a multi-component, hierarchically porous particle of 50–100 μm diameters and consists of catalytically highly active phases (zeolites) that are embedded in a matrix consisting of an active component (alumina) and a non-active part made from silica and clay234. During FCC operation, the particles are exposed to harsh conditions (high temperature) and the non-active components of the catalyst particle are added to increase the attrition resistance of the catalyst as well as the hydrothermal stability of the zeolite material567.…”

A Facile Strategy to Prepare Shaped ZSM-5 Catalyst with Enhanced para-Xylene Selectivity and Stability for Toluene Methylation

“…To implement zeolites in large-scale reactors, shaping process of zeolites (i.e. dispersing zeolites in a binder and shaping to the desired shape) is required to avoid high pressure drop in catalyst beds [16].…”

“…Until recently, the need for a better understanding of shaping process is highlighted in the vibrant area of zeolite catalysis [16][17][18]. The zeolite-binder interactions result in multiple effects on catalyst activity, stability and product selectivity, with the type of binder playing a pivotal role [17,[19][20][21].…”