Methyl N-phenyl carbamate synthesis over Zn/Al/Ce mixed oxide derived from hydrotalcite-like precursors

Enhanced Performance of Zirconium-Doped Ceria Catalysts for the Methoxycarbonylation of Anilines

The methoxycarbonylation of anilines stands as an attractive method for the phosgene-free production of carbamates. Despite the high yields obtained for ceria catalysts, the reduction of the amount of side products and the prevention of catalyst deactivation still represent major hurdles in this chemistry. One advantage of ceria is the possibility of tuning its reactivity by doping its lattice with other metals. In the present work, a series of doped ceria-based materials, prepared by substitution with metals, are evaluated in the methoxycarbonylation of 2,4-diaminotoluene with dimethyl carbonate. Among all catalysts, containing Eu, Hf, La, Pr, Sm, Tb, Y or Zr, ceria promoted with 2 mol % Zr exhibited 96 % selectivity towards the desired carbamates, improving the pure CeO₂ catalyst. Density functional theory demonstrates that two descriptors are needed: 1) a geometric factor that governs the reduction of energy barriers for carbamate formation through ureas; 2) catalyst basicity as N-H bonds need to be activated. Assessment in subsequent reaction cycles revealed that the CeO₂ -ZrO₂ catalyst is more stable than bulk CeO₂ , along with the reduction of fouling processes.

An Escape from Noble Metals for Generating Urethanes via Reductive Carbonylation of Nitroarenes over FeSe2/γ-Al2O3 †

The reaction of FeCl3, SeO2, and Pyridine (Py) in the presence of methanol (MeOH) under CO pressure generates a black precipitate, which has been confirmed as ferric di-selenide, FeSe2 through different structure characterization methods. Furthermore, impregnation of 5 wt% of FeSe2 onto γ-Al2O3 exhibits better catalytic performance than FeSe2 due to the highly dispersed and smaller particle sizes ca. 200–300 nm. The reductive carbonylation of nitrobenzene (NB) was investigated over FeSe2/γ-Al2O3 as a heterogeneous catalyst, delivering an excellent yield and high selectivity of methyl-N-phenyl carbamate (MPC). Moreover, a set of reactions was performed with variation in the reaction time, temperature, and pressure to investigate the effects of these factors. In particular, FeSe2/γ-Al2O3 is highly stable and can be recycled for up to five cycles without significant loss in catalytic performance. A mechanistic study was also conducted on this low-cost catalyst system, especially proposing a crucial role of FeSe2 (μ-CO) active species.

Zn/Al/Pb Mixed Oxides as Efficient Heterogeneous Catalysts for the Synthesis of Methyl N-Phenyl Carbamate

Dimethyl carbonate aminolysis is an effective and green pathway for the synthesis of methyl N-phenyl carbamate (MPC), which is an important intermediate for the synthesis of polyurethanes and many other chemicals. In this work, we demonstrate the fabrication of Zn/Al/Pb mixed oxides as efficient and stable heterogeneous catalysts for MPC synthesis. The catalysts are prepared via facile coprecipitation and subsequent thermal annealing. Their micromorphology and physical-chemical properties are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning TEM (STEM), X-ray photoelectron spectroscopy (XPS), and NH3-TPD. The results show that rather than being doped into ZnO and/or Al2O3, PbO is highly dispersed in the ZnO/Al2O3 base forming ultrafine nanoparticles. Despite the weak interactions within the mixed oxides, the high density of active sites generates outstanding catalytic activity and cycling stability for MPC synthesis, with an aniline conversion of almost 100% and MPC yield of up to 90% during six repeated tests, providing great potential for their further application.