Catalysis 2023 Issue

Benefits of simultaneous mesoporisation/metal incorporation With the emerging shift towards a sustainable and renewable refining and petrochemical industry, the use of tailored metal-based catalysts is likely to intensify

Danny Verboekend and Martin d’Halluin Zeopore Technologies

B y combining mesoporisation with metal incorpora- tion, a platform has been created with enormous synthetic and catalytic potential, applicable to most non-noble metals and any zeolite. The metal-containing mesoporous zeolites obtained display near 100% disper- sions, unprecedented combinations of boosted Lewis acid- ity and preserved Bronsted acidity, and stability in aqueous solutions. Activity and selectivity benefits in dewaxing and methanol-to-olefins demonstrate the potential of this novel approach to catalyst manufacturing. The benefits of these materials in other catalytic applications are currently being explored, with the f ocus on commercialising this technol- ogy in established and emerging applications. Mesoporous zeolites Mesoporous zeolites complement intrinsic zeolitic micro- pores (0.5-1 nanometer) with a network of secondary mesopores (2-20 nanometer). This way, access and diffu- sion limitations are removed, yielding superior performance and attractive business cases in various applications, such as cracking, isomerisation, and alkylation. 1 Within the discipline of mesoporisation, Zeopore’s tech- nologies are scalable and commercially applicable, not rely- ing on elaborate unit operations and/or exotic ingredients. Moreover, in-house scientific experience and the width of the technology toolbox facilitate obtaining the most out of any zeolitic material, from USY to ZSM-5 and from zeolite to SAPO. Relevance of metal-containing zeolite catalyst In many zeolite-based catalytic applications, a metal func- tion is included to yield optimal performance. For example, in hydroprocessing reactions, such as cracking and isomerisa- tion dewaxing, nickel is deposited on the catalyst to provide the required hydrogenation function. In other cases, a specific interaction with the to-be-converted substrate is achieved using metal-loaded zeolite powders, as is the case in selec- tive catalytic reduction of NOx using Cu-based zeolites. Yet in other cases, the zeolite facilitates sorption and combination of species first converted by the metal compo - nent, such as in Fischer-Tropsch chemistry. Metals can also be employed not for a direct role in the catalytic cycle but to tailor acidity and stability, such as the use of rare earths (RE) in fluid catalytic cracking.

With the emerging shift towards a sustainable and renewable refining and petrochemical industry, the use of tailored metal-based catalysts is likely to intensify. Many heavy biomass-derived oil streams benefit from qualita - tive hydroprocessing, first to lower the oxygen content (for example, using a Ni-ZSM-5-based hydrodeoxygenation process) and then to obtain the desired cloud and boil- ing points in dewaxing and hydrocracking (HDC) steps, respectively. Moreover, with these emerging applications, the conver- sion of methanol, syngas, and aromatics predominates, often relying on specific metal-containing zeolites, such as Ga- and Zn-ZSM-5. Finally, especially for oxygen-rich streams, such as sugars, conversions towards desired products, such as lactic acid, are preferably achieved using metal-containing highly Lewis acidic zeolites, such as Sn-beta. Simultaneous mesoporisation and metal deposition The simultaneous mesopore formation and metal deposi- tion occurs using an elegant process, in which both the porosity and composition can be easily tuned (see Figure 1 ). The obtained metal-containing zeolites can subse- quently be shaped into a catalyst extrudate. Hence, the method of metal deposition is fundamentally different com- pared to standard metal-containing catalysts, in which first an extrudate is made, to be subsequently complemented with a metal using in an impregnation step. The metal-containing mesoporous zeolites can be finely tuned towards any application. It has thus far proven par- ticularly effective for alkaline earth and transition metals, such as Mg, Ca, Co, Fe, Cu, Ni, and Zn. Yet also metalloids, such as Sn and Ga, and lanthanoids, such as Ce, have proven suitable candidates. Like metal-free mesoporous zeolites, the secondary porosity can be finely tuned towards applications. Typical mesopore surface areas range from 100-300 m 2 /g. These can be combined with metal contents ranging from very low, ca 100 ppm, to very high, ca. 25 wt%. Traditionally, the deposition of metals on zeolite powder is quickly disregarded, as impregnation of powder in general is a challenging unit operation. Moreover, the metal-zeolite interaction is traditionally suboptimal, resulting in large metal particles (see Figure 2 , top right). In contrast, Zeopore’s metal

Catalysis 2023