MnO₂polymorphs for catalytic carboxylation of 1-butanamine by CO₂

N,N′-dibutylurea is an important fine chemical/intermediate with a wide range of applications. Here, the synthesis of N,N′-dibutylurea through catalytic carbonylation of 1-butanamine by CO₂over MnO₂heterogeneous catalysts was systematically investigated. Four polymorphs of MnO₂, including α-MnO₂, β-MnO₂, δ-MnO₂and γ-MnO₂with various morphological shapes were synthesized by hydrothermal method through altering the synthesis conditions (raw materials or parameters). Significant impact of the lattice structure of the MnO₂oxides on the catalytic activity was demonstrated. Among them, δ-MnO₂possessed the most favorable catalytic activity with N,N′-dibutylurea yield as high as 85.78 % at 160» °C for 24» h in CO₂, while it is only 76.70 % for the α-MnO₂, although they showed the similar specific surface area of around 10» m²» g^-1. To understand the different catalytic behaviors among the different structured MnO₂, the catalysts were characterized by X-ray photoelectron spectroscopy and temperature-programmed desorption of CO₂. It was discovered that the excellent performance of δ-MnO₂was ascribed to its high surface basicity from its high concentration of lattice oxygen on surface of MnO₂, while the large amount of surface unsaturated coordination manganese also positively affected the catalytic performance of γ-MnO₂.