Decomposition Of Hydrogen Sulifde In Non-Thermal Plasma Aided By Semiconductor Catalysts

Hydrogen sulfide (H2S) is a waste gas produced from a variety of natural and man-made sources. According to incomplete statistics, the amount of H2S production has reached to7million tons per year in China. Because of its high toxicity and offensive odor, H2S is converted to nontoxic elemental sulfur and water by the Claus process in industries. Unfortunately, the hydrogen component in H2S is wasted as low-value steam. Therefore, the decomposition of H2S into molecular hydrogen and elemental sulfur has been considered for hydrogen production. In this work, we demonstrated that semiconductor catalysts significantly enhanced the conversion in a non-thermal plasma-induced decomposition of H2S, achieving full conversion at reasonably low energy consumption. The mechanism of the plasma-induced H2S decomposition with an aid of a semiconductor catalyst was proposed. Moreover, a series of catalysts were prepared, which exhibited high catalytic activities for H2S decomposition in plasma.A non-thermal plasma aided by semiconductor catalysis offers an energy-efficient approach to produce high purity hydrogen by H2S decomposition. The significantly improved conversion and energy efficiency in this approach are due to the considerable contribution of the h+and e-on semiconductors generated by both strong electric field and UV-visible light irradiation across the discharge gap.Effects of specific input energy (SIE), reactor structure, diluent gases, feed flow rate, hydrogen production, and metal sulfide loading on the performance of H2S decomposition were studied. The results showed that H2S conversion increased with SIE. Increasing the inner diameter of reactor led to a decrease in the the population of high energy electrons, and thus to a decrease in H2S conversion. Argon was a favorable diluent gas in the conversion of H2S. H2S conversion increased with decreasing the H2S concentration. H2S decomposition was not significantly affect by the residence time, because the gas phase decomposition induced by plasma is a very fast reaction. In the presence of catalyst, the introduction of hydrogen increased H2S conversion, but the promoting effect of hydrogen was not involved in the semiconductor-catalyzed steps. A maximum activity was observed at a loading of10%for CdS/Al2O3and ZnS/Al2O3. The long-term test indicated that these catalysts were stable. A series of ZnxCd1-xS/Al2O3solid solutions with different Cd/Zn molar ratios were prepared, and characterized by different techniques. The catalytic performances of catalysts were investigated in the plasma-induced H2S decomposition. Zno.4Cdo.6S/Al2O3and Zn0.6Cd0.4S/Al2O3catalysts showed the highest activity for H2S decomposition, which can be attributed to their excellent visible-light responsive property and suitable VB and CB positions.Cr doped ZnS/Al2O3catalysts with different Cr/Zn molar ratios exhibited higher performance than ZnS/Al2O3, achieving full conversion at a reduced energy cost. The optimum Cr/Zn molar ratio was found to be0.20. The Cr doping led to a decrease in the particle size and the band gap and an increase in the Zn vacancies, which enhances the catalytic efficiency of ZnS/Al2O3.Al2O3supported metal sulfides, including CdS, ZnS, CoS, FeS2, Ag2S, MnS, NiS, MoS2, CuS and WS2, were prepared by non-thermal plasma. The plasma method not only reduces the preparation time and temperature but also achieves an increased dispersion, small sulfide cluster size, and uniform distribution, as compared to the traditional thermal method. Calcination is not needed in this novel approach. The CdS/Al2O3and ZnS/AlO3catalysts prepared by plasma exhibited a high performance for hydrogen production from H2S.