Construction Of Ag-MnO₂ Catalyst And Its Performance For Toluene Catalytic Oxidation

In recent years, transition metal-oxide-supported noble metal catalysts have been proved to be promising catalysts for the application of VOCs oxidation at lower temperatures. With its exceptional capacity to store and release oxygen, Mn-base catalysts can shift among different valences revealing an excellent redox performance. Meanwhile, silver, a kind of noble metal with relative acceptable price, is often used as an active component of catalysts to promote the toluene oxidation. In order to remove VOCs more effectively, the Ag/MnO2 catalysts have been modified properly. Nanosized ?-MnO2 with different structures have been prepared via the hydrothermal method. The small size and high dispersion Ag nanoparticles supported on the surface of MnO2 are prepared by liquid-phase chemical reduction. A series of x% Ag/MnO2 catalysts are obtained by changing the amount of Ag.1. The Ag/MnO2 catalysts with different morphologies (wire-like, rod-like and tube-like) are used as toluene oxidation catalysts in an attempt to investigate how the morphology of support affects the synergy of Ag and MnO2 and the toluene oxidation activity. Analysis reveals that the morphologies of MnO2 influence the particle size and dispersion of silver particles and the combination of silver particles with MnO2, and then affect the interaction between Ag and MnO2. The small particle size and hemispherically shaped Ag particles induce the surface electrons transformation from Ag surface to MnO2, which lead that Ag has an affinity to the binding sites, and making the interaction of two parts stronger. This specific form of Ag particle can be easily formed and homogeneously dispersed on the surface of wire-like MnO2, and the Ag/MnO2 nanowires catalyst shows the strongest interaction. The strongest synergy can promote the low-temperature reducibility of support and generate more lattice oxygen in metal oxides. The abundant lattice oxygen species increase the catalytic activity.2. The toluene catalytic oxidation activities are investigated by adjusting the Ag loading. The process and mechanism of toluene adsorption-oxidation on the surface of catalysts are discussed. The catalytic performance is significantly affected by the addition of silver and reactive activity is directly related to the silver loading. With the increase of silver loading, the particle size of silver increases, and Ag has a poor attachment to the MnO2 support. When the silver loading is 4%, the hemispherically shaped Ag particles can be finely dispersed on MnO2 support with a small size, which shows the strongest interaction and promotes the redox properties of MnO2. The synergy between Ag and MnO2h is more advantageous to improve the toluene oxidation activity at low temperature phase based on the TEM and reaction activity results. Meanwhile, the appropriate amount of Ag cause the generation of more lattice oxygen species, and then abundant active lattice oxygen species can effectively oxidize the toluene adsorbed on the surface of catalysts, so that it is easier to form carboxylate intermediate over Ag/MnO2 catalysts in the low temperature.4%Ag/MnO2 catalysts exhibit outstanding catalytic performance at low temperature and high temperature. The toluene conversion reaches 40% at 180? and toluene can be completely oxidized into water and carbon dioxide at a temperature as low as 220?.