Ruthenium‐Based Catalysts Supported on Lanthanum and Carbon‐Modified Alumina for Low‐Pressure Ammonia Synthesis

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Abstract
Low‐pressure ammonia synthesis technology holds revolutionary significance in ensuring food security, promoting energy transition, and addressing climate change. However, the hydrogen poisoning of catalysts has long restricted the development of low‐pressure ammonia synthesis processes. Focusing on the regulation of support surface properties, this study successfully prepared a Ru/Al 2 O 3 ‐La‐C catalyst. By regulating the transfer and desorption pathways of hydrogen on the catalyst surface, the hydrogen poisoning phenomenon under low‐pressure conditions was effectively alleviated. Under the reaction conditions of 400°C and 3 MPa, the ammonia synthesis yield of the Ru/Al 2 O 3 ‐La‐C catalyst reached 4.74 mmol NH 3 ·g cat −1 ·h −1 , which was 10 times higher than that of the unmodified Ru/Al 2 O 3 catalyst. Meanwhile, the reaction order of hydrogen changed from −0.43 to 0.58, and the reaction order of nitrogen changed from 0.98 to 0.44, further confirming that the hydrogen poisoning issue of the catalyst was significantly improved and the activation of nitrogen was promoted. Characterization results from H 2 ‐TPD and H‐D exchange experiments showed that La doping constructed La‐O sites, which facilitated the transfer of active hydrogen from the active component Ru to the support. In contrast, the introduction of carbon regulated the recombination and desorption mode of hydrogen on the surface of metallic Ru, prompting hydrogen to desorb in the form of H 2 instead of forming H 2 O. This study provides a new insight for the design and development of catalysts for low‐pressure ammonia synthesis.

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