Origin of Nb₂O₅ Lewis Acid Catalysis for Activation of Carboxylic Acids in the Presence of a Hard Base

Abstract

The Nb2O5 surface catalyzes the amidation of carboxylic acids with amines through Nb5+ Lewis acid activation of the C=O group. In this work, DFT calculations were applied to theoretically investigate the C=O bond activation of a model carboxylic acid (acetic acid) on θ‐Al2O3(110), anatase TiO2(101), and T‐Nb2O5(100) surfaces. The adsorption sites, adsorption energies, reaction energy barriers, electronic properties, and vibrational frequency of acetic acid were examined in detail. It was found that the bond activation of the carbonyl group is most efficient on Nb2O5, although the adsorption energy is larger on Al2O3 and TiO2. The most efficient C=O bond activation on Nb2O5 results in the lowest energy barrier of C−N bond formation during amidation. The Nb2O5 surface also shows larger tolerance to methylamine and water molecules than Al2O3 and TiO2 surfaces. These crucial factors contribute to the highest amidation catalytic reactivity on Nb2O5. Furthermore, the position of the mean density of states of the d‐conduction band of the active metal site relative to the Fermi energy level correlates well with the efficiency in the C=O bond activation and, consequently, the catalytic activity for amidation. These results suggest that, unlike a classical understanding of strong acid sites of metal oxide surfaces, interaction of a carbonyl HOMO with an unoccupied metal d‐orbital, or, in other words, covalent‐like interaction between a carbonyl group and metal adsorption site, is relevant to the present system.

The mechanistic investigation on hydrogen donation performance of bio-acids over bi-functional carbon nanotube catalysts

“…revealed Mo improved the adsorption energy of AcOH dramatically compared with the adsorption onto non-metal loading CNTs, confirming the binding promotion effect of Mo to the AcOH adsorption, in line with recent study [5]. Over Mo/N p -CNT, AcOH exhibited higher binding energy, ascribed to the unpaired electron of pyridinic N acts as electron acceptor (Lewis acid), such that reinforces the binding between the catalyst and adsorbate molecule [34]. This is also confirmed by the lower adsorption energy of AcOH molecule over Mo/CNT.…”

Lewis Acid Catalysis of Nb2O5 for Reactions of Carboxylic Acid Derivatives in the Presence of Basic Inhibitors

“…In order to further support these experimental observations, DFT calculations were employed to theoretically investigate the C=O bond activation of a model carboxylic acid (acetic acid) on the T-Nb 2 O 5 (100) surface. [91] The bulk structure of T-Nb 2 O 5 as well as its surface structure, T-Nb 2 O 5 (100), which should have the lowest surface energy, are shown in Figure 5. [20] For Table 3.…”

Gold‐Palladium Nanocluster Catalysts for Homocoupling: Electronic Structure and Interface Dynamics

“…In these works, we demonstrated that the reactivity is controlled in delicate energetics and by some predominant factors. For example, the reactivity is correlated to the d ‐band center of each metal atom and the perimeter site, i. e. interface between NC and support, is relevant as the catalytic center ,. We also systematically investigated the geometric structure and bond activation of bimetallic Cu−M (M: group 8–11 metals) NC; in particular, the catalytic activity of Cu−Rh NC .…”

“…For example, the reactivity is correlated to the d-band center of each metal atom and the perimeter site, i. e. interface between NC and support, is relevant as the catalytic center. [44,46] We also systematically investigated the geometric structure and bond activation of bimetallic CuÀM (M: group 8-11 metals) NC; [47] in particular, the catalytic activity of CuÀRh NC. [48] Through these systematic studies on NC catalysts, we have clarified some important aspects of the NC catalysts.…”