Effect of basicity on the catalytic properties of Ni-containing hydrotalcites in the aerobic oxidation of alcohol

Abstract

A series of Ni-containing hydrotalcites with different basicities have been prepared by introducing different Mg 2+ contents, and characterized by XRD, SEM, TG-DTG, ICP, FTIR, Hammett analysis, DR UV-Vis, XPS, et al. The effects of basicity on the catalytic performance in the selective aerobic oxidation of alcohols and the mechanism have been studied. The results showed that substituting Ni 2+ in the structure by Mg 2+ ions significantly increased the surface basicity of the catalysts. The surface basicity of Ni-containing hydrotalcites could accelerate the first acid-base reaction step in the oxidation and improve the catalytic activity. Varied alcohols were tested and discussed in the reaction system to verify the effect, and the results indicated that the activity of α-C-H bond is the key factor for the benzyl alcohol derivatives, while the first base-acid reaction step may be more important for aliphatic alcohols. The comparison results between the hydrotalcites and the calcined samples showed that the type of basic site have significantly influence on the catalytic activity, and only the Brønsted OH basic sites accelerate the oxidation. In addition, a probable mechanism for the reaction was postulated based on catalytic results, Hammett and a series of controlled experiments. The main factors affecting the catalytic oxidation of varied alcohols using molecular oxygen as the ultimate oxidant have been discussed, which may be helpful in designing more efficient catalyst.

Effect of Calcination Temperature on Mg-Al Layered Double Hydroxides (LDH) as Promising Catalysts in Oxidative Dehydrogenation of Ethanol to Acetaldehyde

“…Some common features of layered material, sharp and symmetric diffraction peaks in 2θ range of 10-25 and broad diffraction peaks in 2θ range of 30-50 , were observed for non-calcined Mg-Al-000 sample 10 12 . The basal spacing d 003 reflection of Mg-Al-000 was 7.67 Å at 2θ of 11.5 , indicating that the interlayer of Mg-Al-000 was mainly carbonate ion, water and hydroxide ion 13 . For all catalysts calcined between 450-900 , the diffraction peaks were observed at 2θ 43 and 63 , which were attributed to a periclase MgO phase 10,14 , and diffraction peaks of layered structure disappeared.…”

“…The sharp peak at 1359 cm 1 with a shoulder at 1559 cm 1 corresponded to symmetric and asymmetric stretching absorption of C-O and C O in interlayered carbonate ion 11,16 . The broad peaks in the range of 400-1000 cm 1 correspond to stretching absorption of Mg-OH or Al-OH 13,17 . From the results, the absorption bands of interlayer water and hydroxyl groups decreased as calcination temperature increased indicating that calcination of Mg-Al LDH samples resulted in water removal and dehydroxylation.…”

Glycerol aerobic oxidation to glyceric acid over Pt/hydrotalcite catalysts at room temperature

“…The actual Mg/Al ratio and Pt loading are determined by inductively coupled plasma atomic emission spectrometer (ICP-AES), which accord with the theoretical values. In addition, re-Mg x Al 1 -LDH-Pt samples were titrated with benzoic acid dissolved in toluene and the amount of basic sites was labeled using the amount of benzoic acid used per mass of sample [30][31][32]. As listed in Table 1, the concentration of surface basic sites increases with the enhancement of Mg 2+ content, from 0.07 mmol g -1 (re-Mg2Al1-LDH-Pt) to 0.27 mmol g -1 (re-Mg 8 Al 1 -LDH-Pt).…”

Ternary Hydrotalcites in the Multicomponent Synthesis of 4H-Pyrans

“…On the other hand, the reflections at high 2θ angles with (110) and (113) planes indicate an adequate distribution of the anions in the intermediate layer and of the cations in the sheet layer [25]. The unitary cell parameters a and c calculated from the XRD results in Table 1 show that there is no significant change in the LDH-Mg with the incorporation of another divalent cation, and the hydrotalcite structure is maintained.…”

“…All materials show characteristic hydrotalcite-type bands. A predominant band between 3400 and 3700 cm −1 corresponds to -OH stretching vibrations of the hydroxyl groups and water molecules found in the interlaminar region, while a bending band at 1639 cm −1 is assigned to the water molecules present between the layers [25,32]. The band at 1384 cm −1 is attributed to the antisymmetric stretching mode of carbonate anion in the interlaminar layer, while other bands at 625 and 823 cm −1 are related to vibrational modes of CO 3 2− [1,33].…”