Controllable Acid/Base Propriety of Sulfate Modified Mixed Metal Oxide Derived from Hydrotalcite for Synthesis of Propylene Carbonate

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.

Efficient Synthesis of C4 Compound with Low Carbon Emission from Acetaldehyde: Aldol Condensation Catalyzed by Regulable Acidic–Alkaline Al/Mg Sites of CuMgAlO

“…Besides, from Figure c and d and Figures S1 and S2, the SEM patterns of the samples before and after calcination have presented a transformation from the typical lamellar petal structures of the LDH precursors to the collapsed scattered LDO cluster particles. This is consistent with the degradation trend of the diffraction peak of the XRD pattern …”

“…As presented in Figure S3, with the increase of copper content, the absorption kurtosis at 927 cm –1 decreases obviously, which indicates the change in the lattice vibration of interlayer cations M (Mg 2+ , Al 3+ ) with further doping of Cu 2+ . This could be the reason for the degradation of the diffraction peak intensity at the phases of [110] and [113] as shown in Figure a …”

“…It can be explained as the better electron absorption ability resulting from the stronger electronegativity of Cu, making the central aluminum atom in MgAlO more electron deficient to produce more Lewis acid sites . However, after further addition of Cu 2+ , the unavoidable Jahn–Teller effect could finally lead to distortion and breaking up the laminate, covering the acidic sites in LDO. , The total alkalinity of MgAlO reached a maximum of 0.936 mmol/g in all catalysts. The obvious decline in alkalinity can be explained by a similar explanation (Figure b and Table ).…”

“…Acid–base synergistic catalysis is an important factor for the self-condensation of acetaldehyde. Inverse gas chromatography (IGC) is a gentle method to determine acidities and alkalinities of heat-sensitive materials at the temperatures below 393 K. ,, The results of the IGC test are shown in Table , where K a is the acidic parameter and K b is the basic parameter. The K a values of X/CuMgAlO were all larger than those of MgAlO, indicating that the introduction of Cu can increase the acidity of the material surface.…”

“…Hydrotalcite is a kind of inorganic acid–base bifunctional catalyst with a strong base and weak acid. Tunable acid–base bifunctional mixed metal oxide catalytic materials can be obtained after calcination by adjusting the chemical composition and ratio of the former hydrotalcite precursors. , In our previous works, we have verified that the introduction of heteroelements could modify the surface acidity of MgAlO quantitively . With the addition of Cu species, the acidity in the layered double hydroxide (LDH) or layered double oxide (LDO) can be changed due to the Jahn–Teller effect, inducing the shattered lamellar layer of LDH/LDO to expose more acidic sites .…”