Efficient Dry Impregnation of Zirconium into H‐ZSM‐5 Zeolites

• Published in: European journal of inorganic chemistry Vol. 2022; no. 24
• Main Authors: Macedo, Vinícius, Lima, Rafael O. P., Piva, Diogenes H.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 26.08.2022
• Subjects: Acids; Hierarchical zeolites; Infrared spectroscopy; Inorganic chemistry; Lewis acid; Precursors; Solid-state reactions; Solventless processes; Spectrum analysis; Zeolites; Zirconium; Zirconium dioxide
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.202200240

There is considerable interest in adjusting the acidity and pore architecture of zeolites. Herein, we present solventless incorporation of zirconium (∼2–10 wt.%) in a precursor and desilicated (0.2 and 0.4 mol L−1 NaOH) H‐ZSM‐5 zeolite. Infrared and UV‐vis‐DR spectroscopy confirmed the grafting of highly dispersed Zr in all the zeolites. XRD indicated the presence of ZrO2 in zeolites with higher Zr contents. The micropore volume of the precursor zeolite decreased by ∼10 %, suggesting the presence of Zr mainly on the external surface, while it decreased more than 20 % for the desilicated sample, suggesting Zr had access to the micropores at higher Zr contents. Infrared spectroscopy after pyridine adsorption provided evidence for the Brønsted and Lewis acid sites in all zeolites, but the Brønsted acid‐to‐Lewis acid site ratio decreased by >50 % depending on the Zr and NaOH concentrations. The presence of Zr critically changed the predominant nature of the acid sites of the desilicated zeolites. Postsynthesis modification of H‐ZSM‐5 zeolites by desilication and solventless Zr impregnation broaden their spectrum of applications as catalysts and improve the environmental effect of the methodology. Although XRD identified ZrO2, infrared and UV‐vis‐DR spectroscopy confirmed the grafting of dispersed Zr atoms and the presence of both Brønsted and Lewis acid sites.