Catalytic and Sulfur-Tolerant Performance of Bimetallic Ni–Ru Catalysts on HI Decomposition in the Sulfur-Iodine Cycle for Hydrogen Production

The sulfur-iodine (SI) cycle holds great promise as an alternative large-scale process for converting water into hydrogen without CO2 emissions. A major issue regarding the long-term stability and activity of the catalysts is their poor sulfur deactivation resistance in the HI feeding process. In this work, the effect of Ru addition for enhancing the activity and sulfur resistance of SiO2-supported Ni catalysts in the HI decomposition reaction has been investigated. The presence of H2SO4 molecules in the HI results in severe sulfur deactivation of the Ru-free Ni/SiO2 catalysts by blocking the active sites. However, Ni–Ru/SiO2 catalysts show higher catalytic activity without sulfur-poisoning by 25% and exhibit more superior catalytic performance than the Ru-free catalyst. The addition of Ru to the Ni/SiO2 catalyst promotes the stability and activity of the catalysts. The experimental trends in activity and sulfur tolerance are consistent with the theoretical modeling, with the catalytic activities existing in the order Ni/SiO2 < Ni–Ru/SiO2. The effect of Ru on the improvement in sulfur resistance over Ni-based catalysts is attributed to electronic factors, as evidenced by theory modeling analysis and detailed characterizations.

Experimental Study on Sulfur Deactivation and Regeneration of Ni-Based Catalyst in Dry Reforming of Biogas

The dry reforming of methane (DRM) using biogas and a Ni-based catalyst for syngas production was studied experimentally in this study under the presence of H2S. Using the nonpoisoned DRM performance as a comparison basis, it was found that the catalyst deactivation by the sulfur chemisorption onto the catalyst surface depends on both reaction temperature and time. With low reaction temperatures, a complete sulfur coverage was resulted and could not be regenerated. With higher reaction temperatures, the H2S coverage decreased, and the poisoned catalysts could be regenerated. The experimental results also indicated that a catalyst deactivation could not be avoided by using the bi-reforming of methane by adding O2 or H2O simultaneously in the reactant due to the stronger chemisorption capability of sulfur. The catalyst could only be regenerated after it was poisoned. The experimental results indicated that the high-temperature oxidation process was the most effective process for regenerating the poisoned catalyst.

Simple physical mixing of zeolite prevents sulfur deactivation of vanadia catalysts for NOx removal

NOx abatement has been an indispensable part of environmental catalysis for decades. Selective catalytic reduction with ammonia using V2O5/TiO2 is an important technology for removing NOx emitted from industrial facilities. However, it has been a huge challenge for the catalyst to operate at low temperatures, because ammonium bisulfate (ABS) forms and causes deactivation by blocking the pores of the catalyst. Here, we report that physically mixed H-Y zeolite effectively protects vanadium active sites by trapping ABS in micropores. The mixed catalysts operate stably at a low temperature of 220 °C, which is below the dew point of ABS. The sulfur resistance of this system is fully maintained during repeated aging/regeneration cycles because the trapped ABS easily decomposes at 350 °C. Further investigations reveal that the pore structure and the amount of framework Al determined the trapping ability of various zeolites.