(673f) Ammonia Reforming of Ethane over Re Supported HZSM-5 Catalyst

Production of H₂ as a green source of energy for fuel cells and power generation has grasped considerable attention in the academy and industry. Currently, Steam Methane Reforming (SMR) stands for more than 90 % of H₂ supply in the US, producing a huge amount of undesired CO₂ (13 kg/ kg H₂) by-product. Here, in a search for a more environmentally benign alternative for H₂ production, for the first time, we introduce Ammonia Reforming of Ethane (ARE) over Re supported ZSM-5 catalyst as a promising CO_x-free process.

We prepared a series of Re (0.5-10 wt%) supported on HZSM-5 (Si/Al₂: 80) catalysts through impregnation. The performance of as-prepared samples was examined for ARE at atmospheric pressure, reaction temperature of 650 °C, feed composition of 50% NH₃, 25% C₂H₆, and 25% Ar, and space velocity of 6600-132000 hr^-1. As shown in Fig. 1, for the samples with a Re concentration below 186 μmol/gr, the space time yield of products at steady state linearly changes with Re concentration, confirming the identical active site drives the reaction. This represents an identical Turnover Frequency (TOF) value of 3.3 s^-1 for H₂ production regardless of Re concentration. Likewise, the relatively similar TOF of 0.8, 0.06, and 0.1 s^-1 are also observed for HCN, CH₃CN, and CH₄, standing for 75, 18, and 7 % of hydrocarbon selectivity, respectively. Additionally, the present Re/HZSM-5 catalyst also demonstrated considerable stability and negligible coke formation over 80 hr catalytic test.

According to XAS, Raman, HR-TEM, and NH₃-TPD analysis, in the case of fresh samples, Re-oxo species anchored to the Brønsted acid sites are the most dominant species. Interestingly, for the used catalyst, the majority of Re moieties retain their initial structure as Re-oxo species, though the presence of ReO_x nanoparticles in the outer surface of zeolite was also observed.