Characterization of Thermally Stable Brønsted Acid Sites on Alumina‐Supported Niobium Oxide after Calcination at High Temperatures

Abstract

Thermally stable Brønsted acid sites were generated on alumina-supported niobium oxide (Nb2O5/Al2O3) by calcination at high temperatures, such as 1123 K. The results of structural characterization by using Fourier-transform infrared (FTIR) spectroscopy, TEM, scanning transmission electron microscopy (STEM), and energy-dispersive X-ray (EDX) analysis indicated that the Nb2O5 monolayer domains were highly dispersed over alumina at low Nb2O5 loadings, such as 5 wt%, and no Brønsted acid sites were presents. The coverage of Nb2O5 monolayer domains over Al2O3 increased with increasing Nb2O5 loading and almost-full coverage was obtained at a loading of 16 wt%. A sharp increase in the number of hydroxy groups, which acted as Brønsted acid sites, was observed at this loading level. The relationship between the acidic properties and the structure of the material suggested that the bridging hydroxy groups (Nb-O(H)-Nb), which were formed at the boundaries between the domains of the Nb2O5 monolayer, acted as thermally stable Brønsted acid sites.

Synthesis of Fluoride-Containing High Dimensionally Structured Nb Oxide and Its Catalytic Performance for Acid Reactions

“…For this purpose, a pyridine adsorption IR experiment was carried out. This method is useful for distinguishing the type of acid site (either Brønsted acid site (B site) or Lewis acid site (L site)), since pyridine adsorbed over the B site and that adsorbed over the L site give different IR bands. , The IR spectra of 0NbFO and 0.5NbFO after pyridine adsorption are shown in Figure A. Both of the catalysts showed IR bands at 1540 cm –1 assignable to pyridinium ions formed on the B site and at 1445 cm –1 assignable to coordinated pyridine on the L site.…”

A review on the synthesis and applications of sustainable copper-based nanomaterials

“…Additionally, the doped Nb as a support for the Cu NPs not only creates acidic Brønsted sites in contact with water molecules, but also contributes to reducing the leaching of Cu and aggregation of the Cu NPs during the reaction. 344–350 Additionally, the bimetallic Nb-Cu/ZPS catalyst effectively converted VA to various valeric esters in C1–C5 alcohol media (Fig. 43).…”