Hydrogen sulphide is found in raw fuels such as natural gas and coal/biomass-derived syngas. It is poisonous to catalysts and corrosive to metals and therefore needs to be removed. This is often achieved using metal oxides as reactive adsorbents, but metal oxides perform poorly when subjected to repeated cycles of sulphidation and re-oxidation as a result of complex structural and chemical changes. Here, we show that Zn-Ti-O-based adsorbents with nanofibrous morphology can sustain their initial reactivity and sulphur removal capacity over multiple regeneration cycles. These nanostructured sorbents offer rapid reaction rates that overcome the gas-transport limitations of conventional pellet-based sorbents and allow all of the material to be used efficiently. Regeneration can be carried out at the same temperature as the sulphidation step because of the higher reactivity, which prevents sorbent deterioration and reduces energy use. The efficient regeneration of the adsorbent is also aided by structural features such as the growth of hierarchical nanostructures and preferential stabilization of a wurtzite phase in the sulphidation product.

Although the Clean Air Mercury Rule (CAMR) was recently vacated by the District of Columbia Court of Appeals, efficient mercury (Hg) capture is still an important topic for the coal-fired power plant industry. Several states have Hg emission regulations that are even more stringent than CAMR guidelines. All coals contain Hg, which is released during combustion. Significant research efforts have been made to capture this toxic element before it is released to the atmosphere where it can stay suspended and travel for great distances. A variety of approaches have been examined, among which the injection of sorbent materials such as powdered activated carbon (PAC) is the current method of choice. The work presented here examined the mercury capture capability of various carbon substrates decorated with metal nanoparticles when injected as sorbents. Sorbent injections were carried out in a Hg in air mixture for laboratory-scale screening and in a real flue gas at a coal-fired power plant. It was found that palladium-decorated carbon substrates showed excellent mercury capture capabilities, with total efficiencies greater than 90% in laboratory-scale tests. In the real flue gas, the total efficiency was on the order of ∼60%, comparable to the benchmark commercial sorbent Darco Hg-LH, a brominated PAC, although the tested adsorbents had much lower surface areas. The results of this study are presented herein. Novel mercury capture from a coal-fired flue gas was achieved using carbon substrates decorated with palladium nanoparticles.

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