Theoretical Study of the Catalytic Performance of Activated Layered Double Hydroxides in the Cyanoethylation of Alcohols

Abstract

The layered double hydroxides (LDHs) containing Mg2+, Al3+, and OH– (MgAl-OH), commonly known as meixnerite, meixnerite-like, or activated LDH, act as catalyst in the cyanoethylation of alcohols, for which the catalytic activity depends on the LDH composition, particularly on the ratio R between the amount of Mg2+ and Al3+. It is known that MgAl-OH with R = 3 presents the largest catalytic activity when the reactants are methanol and acrylonitrile. To determine the molecular basis of such behavior, the adsorption of OH–, CH3O–, and H2O on the (001) surfaces of MgAl-OH with compositions R = 2, 3, and 3.5 is investigated using density functional theory. It is found that the peculiar catalytic activity of MgAl-OH in the methanol cyanoethylation reaction correlates with the capability of the MgAl-OH surface to stabilize CH3O–a process in which hydrogen bonding plays a crucial roleand the reactivity of the adsorbed CH3O– lone pairs.

Multiscale Mechanistic Study of the Adsorption of Methyl Orange on the External Surface of Layered Double Hydroxide

“…To investigate the thermodynamic of this system in full, DFT calculation will have to be brought into this methodology to derive the energy of adsorption. 52 The calculated optimum geometry could be further validated by comparing experimental and calculated vibrational spectra. This would be an interesting topic for future work but is out of the scope of the present study.…”

Activated layered double hydroxides: assessing the surface anion basicity and its connection with the catalytic activity in the cyanoethylation of alcohols

“…The deviation of the a and b lattice parameters from 901 in the LDH relaxed structures with 1H layer stacking (see Table 1) leads to a consecutive layer sliding in a direction perpendicular to the [001] direction, making the surface models built using such bulk structures resemble the 3R 1 layer stacking. 19 Interlayer hydroxide anions are located between the trivalent and divalent metallic cations, as suggested by Cuautli et al after a thorough search for the most energetically favored interlayer anion positions. 30 Bulk geometry optimizations are carried out including all internal coordinates and lattice parameters.…”

“…PBE has been successfully used by several groups to investigate the structure and dynamical properties of LDH materials. 18,19,[28][29][30][31][32][33][34][35][36] Moreover, an appropriate description of dispersion is included with the Tkatchenko-Scheffler (TS) method. 37 The combination of PBE with TS gives an adequate description of hydrogen bonding, 38,39 which is a significant contribution to the anionlayer interaction in meixnerite-like LDHs.…”

“…Recently, in a theoretical investigation using DFT and surface models as used in this work, we have shown that the catalytic activity of MgAl-LDH with R = 3 is indeed connected to its ability to stabilize the methoxide anion on its surface, in accordance with the proposed reaction mechanism, but also with the reactivity of the oxygen lone pairs of the methoxide anion. 19 Chemical processes assisted by catalytic surfaces are usually rationalized in terms of the acid-basic nature of the active surface sites. The identification of reactive surface sites and their classification as acidic or basic is thus important for getting insight into the molecular mechanisms driving such chemical processes.…”

LDH Nanocubes Synthesized with Zeolite Templates and Their High Performance as Adsorbents

“…The lamellar structure of LDHs is favored as a catalyst for different practical applications due to its tunable chemical composition, unique structure, nontoxicity, and wide variety of material properties [12,13]. These characteristics allow them to be used as adsorbents [14], and in catalysts [15], fuel cells [16], drug delivery [17], CO 2 capture [18], and many other potential applications. In particular, LDHs exhibit effective performance as an adsorbent for organic pollutants, mainly due to their low cost, positively charged layers with anion exchange capability, colloidal and thermal behavior, and high surface area [19,20].…”