Catalytic Combustion Study of Ethanol Over Manganese Oxides with Different Morphologies
Beibei Feng, Chunlan Qin, Ying Shi, Lidong Zhang
Abstract
Ethanol is extensively used in the transport field as a clean additive and alternative for gasoline in internal combustion engines, although its incomplete combustion inevitably releases harmful species to humans and the environment. Mn-based oxides, one of the most promising materials for catalytic combustion, have attracted considerable interest due to their excellent catalytic performance and low cost. In this work, hydrothermal methods were used to synthesize the different manganese oxides with distinct morphologies (1D-Mn3O4 nanorod, 2D-Mn3O4 nanoplate, and 3D-Mn3O4 nano-octahedron). Meanwhile, catalytic activity over these three catalysts was evaluated for ethanol combustion. The physicochemical properties of these samples were characterized by X-ray diffraction, N2-BET, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Raman, and H2-TPR. Among the three catalysts, the Mn3O4 nanoplate exhibited an optimal performance at a space velocity of 60 000 mL g–1 h–1. The apparent activation energy associated with the nanoplate material (25.6 kJ/mol) was lower than that of the 1D-Mn3O4 nanorod (28.9 kJ/mol) and 3D-Mn3O4 nano-octahedron (37.3 kJ/mol). According to characterization results, the Mn3O4 nanoplate catalyst exhibits a small crystal size, large surface area, more exposed (112) facets, abundant Mn4+, and defective structure, contributing to a superior catalytic performance at the high space velocity of 120 000 mL g–1 h–1. In addition, we conclude that the catalytic combustion of ethanol follows the Mars-van Krevelen mechanism based on the kinetic simulation results of experimental data.