Formation of Subnanometer Zr-WOx Clusters within Mesoporous W-Zr Mixed Oxides as Strong Solid Acid Catalysts for Friedel-Crafts Alkylation

WO3-ZrO2 mixed metal oxides is an important class of acid solid. Here, we successfully synthesized a variety of mesoporous WO3-ZrO2 mixed metal oxides by a well-controlled sol-gel process (AcHE) using Zr(OBu)(4) and WCl6 as the inorganic precursors in the presence of poly block copolymer F127. Their structures and acid properties have been well characterized by XRD, Raman, N-2 adsorption measurement, and HRTEM analyses. In addition, new insights from TG-DSC and P-31 NMR characterization also provide useful information on the formation of strong acidity of this important solid acid. Moreover, their structure-to-properties relationship has been studied in the Friedel-Crafts (F-C) reaction of anisole and benzyl alcohol. We identified that the subnanometer WOx clusters act as the most active sites for the F-C reaction. Most importantly, we show that the formation of these subnanometer WOx clusters can be rationally controlled. It is shown that a minimum W concentration (0.07 at the calcination temperature of 800 degrees C) and a minimum calcination temperature (650 degrees C at a given W concentration of 0.1) are required during the preparation of these acid catalysts for the development of highly active subnano WOx clusters.