Zn Promoted Mg-Al Mixed Oxides-Supported Gold Nanoclusters for Direct Oxidative Esterification of Aldehyde to Ester

Abstract

The synthesis of ester compounds is one of the most important chemical processes. In this work, Zn-Mg-Al mixed oxides with different Zn2+/Mg2+ molar ratios were prepared via co-precipitation method and supported gold nanoclusters to study the direct oxidative esterification of aldehyde and alcohol in the presence of molecular oxygen. Various characterization techniques such as N2-physical adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and CO2 temperature programmed desorption (TPD) were utilized to analyze the structural and electronic properties. Based on the results, the presence of small amounts of Zn2+ ions (~5 wt.%) provoked a remarkable modification of the binary Mg-Al system, which enhanced the interaction between gold with the support and reduced the particle size of gold. For oxidative esterification reaction, the Au25/Zn0.05MgAl-400 catalyst showed the best performance, with the highest turnover frequency (TOF) of 1933 h−1. The active center was believed to be located at the interface between metallic gold with the support, where basic sites contribute a lot to transformation of the substrate.

Ni-Based Hydrotalcite (HT)-Derived Cu Catalysts for Catalytic Conversion of Bioethanol to Butanol

“…Figure 6a depicts the CO 2 -TPD profiles of the above NiMO x supports. Three types of basic sites (i.e., weak basic site: <300 • C, medium basic site: 300~500 • C and strong basic site: >500 • C) can be observed in the profiles [41,49]. The specific amounts of each basic site were calculated by integrating the corresponding peak areas and are summarized in Table 2.…”

Highly Selective and Stable Cu Catalysts Based on Ni–Al Catalytic Systems for Bioethanol Upgrading to n-Butanol

“…Thus, to evaluate the acid-base property, CO2-TPD and NH3-TPD were conducted, respectively, for different supported Cu catalysts. As displayed in Figure 5a, all catalysts show a desorption peak of CO2 at 350~400 °C, implying the presence of mediumstrong basic sites [49]. Notably, for the Cu/Ni3AlOx and Cu/Ni1AlOx, the total amount of CO2 adsorption is obviously larger than that of the Cu/NiO and Cu/Al2O3, implying the catalysts possess much more basic sites than those of the Cu/NiO and Cu/Al2O3, which are derived from the abundant interlayer hydroxyl groups of Ni-Al-LDH.…”

Ag substituted Au clusters supported on Mg-Al-hydrotalcite for highly efficient base-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

“…This suggested that the interlayer distance of MgAl-HT decreased correspondingly owing to the collapse of the lamellar hydrotalcite structure after heat treatment. 48,49 Nevertheless, the deposition of Au and Au-Ag NCs onto the support could greatly enhance the stability of hydrotalcite after calcination, since the diffraction peaks of (006) appeared again in the patterns, and the values of d 003 were between that of MgAl-HT and MgAl-300. Besides, no obvious diffraction peaks assigned to metallic Au or Ag could be observed in the spectra, indicating that Au and Au-Ag particles were highly dispersed in the catalysts.…”