Effect of Crystal Phase of MnO₂ with Similar Nanorod‐Shaped Morphology on the Catalytic Performance of Benzene Combustion

Abstract

Four manganese oxides with different crystal structures in the similar nanorod‐shaped morphology were synthesized and investigated for the catalytic combustion of benzene. The physicochemical properties of the materials were characterized by N2 physisorption‐desorption, transmission electron microscope (TEM), X‐ray photoelectron spectroscopy (XPS), Raman spectra, O2 temperature programmed desorption (O2‐TPD) and temperature programmed surface reaction (TPSR). The catalytic activities on benzene combustion over various manganese oxides decreased in the order: γ‐MnO2 > β‐MnO2 > α‐MnO2 > δ‐MnO2. The activation energy of benzene combustion over γ‐MnO2 (67.4 kJ/mol) was lower than that over α‐MnO2 (69.2 kJ/mol), β‐MnO2 (79.1 kJ/mol) and δ‐MnO2 (85.2 kJ/mol). The TPSR results with or without gaseous oxygen revealed that the reaction pathway was occurred via MVK mechanism. The surface adsorbed oxygen species concentration and low temperature O2 desorption of these manganese oxides, determined by XPS and O2‐TPD, decreased in the order of γ‐MnO2 > β‐MnO2 > α‐MnO2 > δ‐MnO2, are in good agreement with the sequence of their catalytic performance on benzene combustion. It is concluded that higher surface adsorbed oxygen species ratio and better low temperature O2 desorption were crucial to the superior catalytic performance of the α‐MnO2, β‐MnO2, γ‐MnO2 and δ‐MnO2 materials.

Recent progresses in the synthesis of MnO2 nanowire and its application in environmental catalysis

“…Hu et al 146 found that the order of catalytic activities on benzene combustion over MnO 2 with different phase structures was γ-MnO 2 > β-MnO 2 > α-MnO 2 > δ-MnO 2 . The surface adsorbed oxygen species concentration and low temperature O 2 desorption of these manganese oxides were in good agreement with the sequence of their catalytic performance on benzene combustion.…”

Morphology Effects of CeO2 Nanomaterials on the Catalytic Combustion of Toluene: A Combined Kinetics and Diffuse Reflectance Infrared Fourier Transform Spectroscopy Study

“…Heterogeneous catalysis generally involves the cleavage and formation of chemical bonds for the reactant and the product on the surface of a catalyst, and these elementary steps could be rationally expected to be closely associated with the coordination environment or active sites of the catalyst surface. − Catalyst morphology is a significant tool to investigate these impacts on heterogeneous catalysis because a morphology-controllable catalyst could expose specific crystal planes, which had different coordination environments. ,,− Therefore, morphology effects have been paid much attention for investigating heterogeneous catalysis.…”

Comparative Study of the Flue Gas Desulfurization Using Different‐Grade Natural Manganese Oxides

“…Based on the analysis of the activity of MnO 2 with different crystal forms, Hu et al. conclude that the activity sequence of these MnO 2 phases is γ ‐MnO 2 > α ‐MnO 2 > δ ‐MnO 2 . The existence of γ ‐MnO 2 could be more favorable to desulfurization.…”