No abstract

Ammonium persulfate modified mixed metal oxide derived from hydrotalcite with tunable acid/base properties can be prepared via thermal decomposition of Mg-Al hydrotalcite-type precursors and ammonium persulfate. By controlling the ammonium persulfate content, these sulphur mutated samples, denoted as SMgAlO-y (y = 1; 3; 5; 7), were investigated in this research. The resulted materials were characterized by XRD, SEM, FT-IR spectra, Py-IR spectra, XPS, Hammett indicator, CO2-TPD, as well as NH3-TPD. Furthermore, the acid-base property of the sample surface was determined by inverse gas chromatography measurements (IGC). Among all the obtained outcomes, the target SMgAlO-5 demonstrated the maximal Ka/Kb value, and it presented the highest activity as a catalyst in the synthesis of propylene carbonate (PC) through 1,2-propylene glycol and urea, giving the yield of 97.2% at the optimized reaction condition, which indicated that the PC yield counted on the synergic effect of the acidity and basicity on catalysts.

A series of CuMgFe layered double hydroxides (denoted as X/CuMgFe–LDHs) with different Cu contents were synthesized by co‐precipitation as catalysts for phenol hydroxylation under mild conditions. The as‐prepared samples were analyzed by X‐ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma emission spectroscopy (ICP‐ES), N2 adsorption–desorption, Fourier transform infrared (FT‐IR), thermogravimetric differential scanning calorimetry (TG‐DSC), X‐ray photoelectron spectroscopy (XPS) and hydrogen temperature‐programmed reduction (H2‐TPR) to investigate the morphologies and physicochemical properties. As presented by the characterization results, introducing a certain amount of copper not only increased the amount of active metal centers but also formed more oxygen vacancies and lattice oxygen to promote electron transport between the double layers in LDHs. However, the excess copper would significantly disrupt the X/CuMgFe–LDH framework, declining the activity. Therefore, the 20/CuMgFe–LDH sample presented the best catalytic performance among all the catalysts in terms of activity, which was correlated with the layered structure, low‐temperature reducibility, oxygen species and low Cu+/Cu2+ and Fe2+/Fe3+ ratios. The catalyst could maintain good stability even after recycling for five times. Finally, a possible mechanism for phenol hydroxylation via Cu+–OV–Fe2+ and Cu2+–O–Fe3+ redox cycles on CuMgFe–LDHs was proposed.

In this work, a series of CuZnFeAl-LDH catalysts for phenol oxidation to dihydroxybenzene have been prepared through coprecipitation method. Versatile characterizations are applied to reveal electron transfer from oxygen vacancies...

Aldol condensation is an optimal method for carbon growth free from the thermo-cleavage technique of fossil resources with high carbon emissions. To further develop a catalyst with high activity and selectivity, a CuMgAl layered double oxide, named X/CuMgAlO, is successfully obtained after calcinating the MgAl hydrotalcite precursor doped with Cu 2+ . The resulting sample is applied as a catalyst in the self-condensation of acetaldehyde to crotonaldehyde. On the basis of the investigation of the reaction conditions, sample 15/CuMgAlO has presented to be the optimal catalyst in the aldol condensation of acetaldehyde to form crotonaldehyde with the conversion and selectivity of 92.3% and 80.4%, respectively. NH 3 -TPD, CO 2 -TPD, IGC, and Py-IR were applied to investigate the synergistic effect of the acidic and alkaline sites. It has been verified that a suitable acidity could be regulated through the addition of Cu species, and more Lewis acidic sites from Al sites can be formed due to the Jahn−Teller effect, the enhanced electronegativity of Cu, and the shattered lamellar layer in the calcinated CuMgAlO. Besides, the relatively mild acid could guarantee high selectivity to the target crotonaldehyde. Considering that aldol condensation could create a new carbon bond without the use of fossil resources, carbon emissions are significantly reduced in the field of fine-chemical synthesis industry.