In-Situ-Generated Active Hf-hydride in Zeolites for the Tandem N-Alkylation of Amines with Benzyl Alcohol

Abstract

[EN] In this work, we have studied the catalytic activity of different silicates (MFI, MCM-41, and Beta) containing Lewis acid sites (including Sn, Ti, Zr, and Hf) for the tandem N-alkylation reaction of aniline with benzyl alcohol. The Hf- and Zr-Beta were the most active catalysts for this transformation, showing in both cases selectivities toward the corresponding N-benzylaniline higher than 97%. FTIR and DFT analyses confirm that the active sites in the Hf-Beta catalyst for this process are the open sites where one of the four Hf-O bonds is hydrolyzed. Moreover, the amount of these active species could be notoriously increased with previous thermal treatment of the Lewis acid zeolite with benzyl alcohol. Isotopically labeled experiments and theoretical mechanistic studies reveal that the N-alkylation reaction occurs through a hydrogen borrowing pathway, in which in situ Hf-hydride species were generated. Finally, the Hf-Beta zeolite was reused several times in the N-alkylation reaction without any appreciable deactivation detected. This catalytic system could be expanded to a variety of amines, including aliphatic and biomass-derived amines. ; This work has been supported by the Spanish Government through "severo Ochoa" (SEV-2016-0683, MINECO), MAT2017-82288-C2-1-P (AEI/FEDER, UE), and RTI2018101033-B-I00 (MCIU/AEI/FEDER, UE). Dr. Susana Valencia is acknowledged for the preparation of the Ti-Beta sample. The Electron Microscopy Service of the UPV is also acknowledged for their help in sample characterization. Part of the computations were performed on the Tirant III cluster of the Servei d'Informa`tica of the University of Valencia. ; Rojas-Buzo, S.; Concepción Heydorn, P.; Corma Canós, A.; Moliner Marin, M.; Boronat Zaragoza, M. (2021). In-Situ-Generated Active Hf-hydride in Zeolites for the Tandem N-Alkylation of Amines with Benzyl Alcohol. ACS Catalysis. 11(13):8049-8061. https://doi.org/10.1021/acscatal.1c01739 ; S ; 8049 ; 8061 ; 11 ; 13