الفهرس 
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Abstract
This thesis study explores the use of various photocatalysts for the removal of elemental mercury (Hg0) from Natural gas. The study begins by introducing the importance of Hg0 removal from Natural gas due to its toxicity and environmental impact. Several types of photocatalysts are then discussed, including TiO2, Ag/TiO2, Co/TiO2, N/TiO2, S/TiO2, Ce0.02Ti0.98O2, and Ti0.75Cu0.25O2. The photocatalytic properties of each catalyst were evaluated using a fixed-bed reactor system, and their efficiencies were compared in terms of Hg0 removal capacity under different wavelengths of irradiation.
the break through curves of Hg0 photo-oxidation and adsorption over Ag/TiO2. As mentioned earlier, the Ag/TiO2 catalyst was less effective at removing Hg0 in the dark conditions compared to undoped TiO2, with a capacity of removal of Hg0 of 8.935 µg/g. However, when the catalyst was exposed to UV light, the capacity of removal of Hg0 increased to 51.912 µg/g. This suggests that the presence of Ag nanoparticles on the surface of the TiO2 catalyst can enhance the photocatalytic process and increase the removal efficiency of Hg0. Furthermore, when the Ag/TiO2 catalyst was exposed to UV-visible light, the capacity of removal of Hg0 further increased to 86.783 µg/g. This indicates that the addition of Ag ions to TiO2 can also broaden the light absorption range of the catalyst and improve its efficiency for the removal of Hg0.
the breakthrough curves of Hg0 photo-oxidation and adsorption over Co/TiO2 that exhibits a higher capacity for Hg0 removal compared to undoped TiO2 under both dark and UV-visible light conditions. This suggests that Co/TiO2 can effectively remove Hg0 from the air in the
absence of light as well as in the presence of both UV and visible light. This is a desirable property for air purification technologies since indoor environments often have limited exposure to UV light.
In summary, the addition of Co ion to TiO2 enhances its photocatalytic activity for the removal of Hg0 due to the formation of a new intermediate band within the band gap, which promotes the movement of electrons from the valence band to the conduction band. The increase in surface area and pore volume of Co/TiO2 also contributes to its enhanced activity for Hg0 adsorption. Co/TiO2 is stable and effective under both UV and visible light irradiation, making it a promising material for the removal of gaseous pollutants such as Hg0 from natural gas
The effect of temperature on the photocatalytic activity of unmodified TiO2 for the oxidation of elemental mercury. The experiments were conducted at three different temperatures (25, 50, and 90°C) using UV light with a wavelength of 253.7 nm. The Hg0 removal efficiency was evaluated using a Q equation and the results were presented as breakthrough curves.
The study found that the Hg0 removal capacity of TiO2 photocatalyst decreased with increasing temperature, with the best removal capacity of 116.663 µg.m-3 observed at 25°C and a spent time of 120 hours. In contrast, the worst removal capacity of Hg0 was observed at 90°C, with a removal capacity of only 16.135 µg.m-3 in 20 hours. The weak intermolecular attraction between Hg0 and TiO2 surface at high temperature was suggested as a possible explanation for the decreased removal efficiency.
The results indicate that the temperature has a significant effect
on the removal efficiency of Hg0 by TiO2 photocatalyst. At higher temperatures, the removal capacity of Hg0 decreases, which could be attributed to the desorption of Hg0 from the TiO2 surface due to weak intermolecular attraction. The highest removal capacity of Hg0 was observed at 25oC, with a removal efficiency of 116.663 µg.m-3 and a spent time of 120 h. This suggests that the temperature should be optimized for maximum removal efficiency when using TiO2 photocatalyst for Hg0 oxidation.
N/TiO2 photocatalysts have shown promise in the removal of gaseous pollutants such as Hg0 in the presence of UV-visible light. Their photocatalytic properties are activated by light, and the movement of electrons between the conduction and valence bands facilitated by the formation of an intermediate energy level helps to generate more electron-hole pairs that can participate in the photo-oxidation of Hg0. The nitrogen ions in the N/TiO2 photocatalyst can create new energy states in the bandgap, which can enhance the photocatalytic activity and improve Hg0 removal efficiency. However, their performance as an adsorbent in the absence of light is inferior to undoped TiO2, which can adsorb Hg0 even in the absence of light due to its non-photocatalytic nature.
The present study investigated the use of S/TiO2 catalyst for the removal of Hg0 from natural gas. The results showed that S/TiO2 had a remarkable effect on the removal of Hg0 in dark conditions due to chemical adsorption and the formation of a chemical bond between Hg0 and sulfur nonmetal ion. Additionally, S/TiO2 demonstrated a significant improvement in Hg0 removal efficiency when used as a photocatalyst, with a removal capacity of 65.415 µg/g, compared to undoped-TiO2,
which only achieved 31.74 µg/g. Moreover, replacing the UV lamp with a UV-visible lamp further improved the performance of the S/TiO2 catalyst, resulting in a removal capacity of 82.798 µg/g, which is much higher than that of pure TiO2. The improvement in photocatalytic activity is attributed to the formation of a new band in the S/TiO2 catalyst between the valence and conduction bands, which enables efficient electron transfer under UV-visible light. These findings suggest that S/TiO2 is a promising material for not only dark Hg0 removal but also for photocatalytic Hg0 removal in natural gas.
The results indicate that the addition of copper to TiO2 to form Ti0.75Cu0.25O2 led to an increase in Hg0 removal capacity due to the formation of an intermediate band between the conduction and valence bands. Similarly, Ce0.02Ti0.98O2 also showed high photocatalytic activity, attributed to its mesoporous structure and the presence of Ce3+ ions. In comparison, the other catalysts showed moderate to low photocatalytic activity.
Furthermore, the study examined the surface properties of Ce0.02Ti0.98O2 after the photocatalytic process for Hg0 using XPS analysis. The results showed that the proportion of adsorbed oxygen in the used catalyst was higher than that in the fresh catalyst, indicating that the adsorbed oxygen was consumed during the Hg0 test.
The XPS analysis of Mesoporous Ce0.02Ti0.98O2 catalyst before and after a catalytic process for Hg0 revealed that the proportion of adsorbed oxygen was higher in the fresh catalyst than in the used catalyst. This suggests that the adsorbed oxygen was consumed during the Hg0 test due to its interaction with mercury. The XPS spectra showed two peaks corresponding to adsorbed oxygen and lattice oxygen, and the
binding energy of the adsorbed oxygen was found to be higher than that of the lattice oxygen. The percentage of adsorbed and lattice oxygen on the catalyst surface was denoted as Oα /OT and Oβ /OT, respectively. The proportion of each type of oxygen was calculated by measuring the integral area of each peak. The XPS analysis provides valuable information about the surface chemistry and electronic state of the catalyst, which can help in the optimization of the photocatalytic process for the removal of Hg0.
In conclusion, this study demonstrates that Ti0.75Cu0.25O2 and Ce0.02Ti0.98O2 are efficient photocatalysts for the removal of Hg0 from air streams. These findings have important implications for the development of effective and sustainable technologies for Hg0 content control. However, further research is needed to optimize the photocatalytic properties of these catalysts and to investigate their long-term stability and practical applicability in natural gas industry.