Effect of zirconia polymorph on the synthesis of diphenyl carbonate over supported lead catalysts

High-Performance Na-CH3ONa/γ-Al2O3 Catalysts for High-Efficiency Conversion of Phenols to Ethers

An efficient alkaline catalyst with a porous structure (Na-CH₃ONa/γ-Al₂O₃) was prepared by the melting method. The wastewater from the semicoke plant (WW_SCP) was extracted multiple times with isometric dimethyl carbonate (DMC)-cyclohexane mixed solvent at room temperature to obtain an organic phase (OP) with a high concentration of phenols. Ether (OPCP) was obtained by catalytic conversion of OP over catalyst Na-CH₃ONa/γ-Al₂O₃ at 210 °C and with a reaction time of 2.5 h. Both OP and OPCP were analyzed with a gas chromatograph/mass spectrometer (GC/MS) and a quadrupole Exactive Orbitrap mass spectrometer (QPEOTMS). The results showed that only DMC, phenol, o-cresol, and other monohydric phenols were detected in OP, and only other saturated ethers such as anisole and O-methylanisole were detected in OPCP. Through the study of the catalytic conversion of the WW_SCP-related model compound, it was found that Na-CH₃ONa/γ-Al₂O₃ could effectively activate (deprotonate) phenol into phenate, and the strong nucleophilic oxyanion of phenate would attack the methyl carbon and carbonyl carbon on DMC to obtain methyl and methoxy groups. Thereby, phenate can be combined with methyl and methoxy groups to acquire the product anisole. In addition, the catalyst Na-CH₃ONa/γ-Al₂O₃ was found to still have high catalytic activity after 10 repeated cycles. It was speculated that this was related to the abundant microporous and mesoporous structure of the catalyst Na-CH₃ONa/γ-Al₂O₃.

Incorporating Pb2+ Templates into the Crystalline Structure of MnO2 Catalyst Supported on Monolith Applications in H2O2 Decomposition

Several MnO₂ catalysts, promoted with Pb²⁺ ions and supported on a wash-coated monolith (WMon), briefly, xPbyMn-WMon (x = 0, 0.5, 1.0, 1.5, 2, and 2.5 and y = 8 wt %), were prepared. The presence of Pb²⁺ affects the manganese oxidation state, crystalline phase, thermal resistance, metal dispersion, and catalytic performance. According to XPS spectra, XRD patterns and HRTEM images, manganese was dispersed on the monolith surface as Mn³⁺ and Mn⁴⁺ species in both α and β crystalline phases. The ratios of Mn⁴⁺/Mn³⁺ states and α/β phases were highly enhanced, and the desired Pb _x Mn₈O₁₆ phase (coronadite) was formed. Concentrations of the defect oxygen (Mn-O-H) and oxygen vacancies, which improve the catalyst reducibility and the MnO₂ reduction temperature, were also increased. Further, based on the H₂ chemisorption analysis, the Pb²⁺ template would increase the manganese dispersion and the reaction sites. Meanwhile, the average MnO₂ crystallite size was decreased from 13.26 to 8.15 nm. The optimum catalyst 1.5Pb8Mn-WMon exhibited an activity 149% more than the manganese-only catalyst in decomposition of H₂O₂. Evaluation of catalyst stability in the presence of Pb²⁺ after 10 recycles showed only a 6.8% decrease. The catalytic reaction was evaluated based on different criteria.

Highly effective transformation of methyl phenyl carbonate to diphenyl carbonate with recyclable Pb nanocatalyst

Diphenyl carbonate (DPC) is a type of versatile industrial chemical, and the disproportionation of methyl phenyl carbonate (MPC) is a key step to produce DPC. However, the design and formulation of a catalyst for the efficient synthesis of DPC is a major challenge due to its small equilibrium constant. The support material is a critical factor influencing the performance of Pb nanocatalysts. Thus, a series of Pb-based catalysts over MgO, ZrO₂, SiO₂, TiO₂ and Al₂O₃ were prepared to investigate the effect of the support materials on the physicochemical properties and catalytic performances for the conversion of MPC to effectively synthesize DPC. The catalysts were well characterized by XRD, BET, TEM, XPS, ICP-OES, H₂-TPR, Py-IR and NH₃-TPD. The results showed that the nature of the support obviously affected the structural properties and catalytic performances, and Pb was dispersed better on SiO₂, TiO₂, ZrO₂ and MgO than on Al₂O₃, and showed stronger metal-support interaction over MgO and ZrO₂. The activity results revealed that PbO/MgO and PbO/ZrO₂ exhibited higher catalytic activities because they contained higher Pb dispersion and more Lewis acid sites, and the catalytic activities followed the order PbO/MgO > PbO/ZrO₂ > PbO/SiO₂ > PbO/Al₂O₃ > PbO/TiO₂. On the contrary, PbO/MgO and PbO/ZrO₂ exhibited better reusability due to strong interaction between the highly dispersed Pb and the supports, and the activity decrease in the case of PbO/SiO₂, PbO/Al₂O₃ and PbO/TiO₂ mainly resulted from the Pb leaching loss. This work would contribute to exploiting novel catalytic materials in a wide range of applications for the efficient synthesis of organic carbonates.