Vertically-oriented Graphenes Supported Mn₃O₄ As Advanced Catalysts In Post Plasma-catalysis For Toluene Decomposition

Volatile organic compounds(VOCs),the third major gaseous pollutants,are detrimental to both human beings and environment.Non-thermal plasma(NTP),featured by the nonequilibrium characteristic between high energy electrons and other particles,has attracted great interest for VOC treatment due to its high decomposition efficiency and quick response at ambient temperature.Hybrid NTP and heterogeneous catalyst system combines the advantages of high selectivity from catalysis and the fast ignition from plasma technique,where the decomposition efficiency of VOCs and selectivity of desired products could be significantly enhanced.This work reports the catalytic performance of catalysts toward toluene decomposition in post plasma-catalysis(PPC)system.Dense networks of VGs were synthesized on carbon paper(CP)via a microwave plasma,enhanced chemical vapor deposition(PECVD)method.A constant current approach was applied in a conventional three-electrode electrochemical system for the electrodeposition of Mn3O4 catalysts on VGs.The as-obtained catalysts were characterized by inductively coupled plasma mass spectrometry(ICP-MS).Experimental results show that the manganese oxide catalyst loading mass on VG-coated CP was significantly higher than that on pristine CP(almost 1.8 times for an electrodeposition current of 10 mA).Moreover,scanning electron microscope(SEM)results show that the decoration of VGs led to a better dispersion of manganese oxide particles.According to the X-ray diffraction(XRD),X-ray photoelectric spectroscop(XPS)and fourier transform infrared spectroscopy(FT-IR)test,results provide concrete evidence for the formation of Mn3O4 nanoparticles.The oxygen O 1s spectra of XPS results are fitted roughly with two peaks,representing lattice oxygen species and surface oxygen species.The surface oxygen species have higher mobility than lattice oxygen,which could positively participate in the reaction of catalytic oxidation.Finally,the catalytic ability of Mn3O4/CP and Mn3O4/VG catalysts were tested in PPC system.The Mn3O4/VG catalysts exhibited a higher ozone conversion rate,which suggests that more atomic oxygen generated on the catalyst surface,promoting toluene oxidation into CO2 and H2O.The results of toluene degradation efficiency,CO selectivity,CO2 selectivity and NOx concentration both shows that Mn3O4/CP have a better catalytic ability than Mn3O4/CP.