Ru-Based Catalysts for Ammonia Decomposition: A Mini-Review

Abstract

Ammonia with a hydrogen content of 17.6 wt % is viewed as a promising hydrogen carrier because the infrastructures for its production, storage, and transportation have been well established. The challenge is that currently the straight production of H2 from NH3 only works at high temperatures. To date, various metal-based catalysts have been developed for NH3 decomposition, among which the Ru-based ones are the most superior due to the suitable Ru–N binding energy. In the past decade, efforts have been put in to improve the performance of Ru-based catalysts, and the target is to lower Ru loading and reaction temperature. A large variety of support and promoter materials were studied, and advanced techniques were employed to disclose the relationship between catalytic performance and catalyst structure. In this paper, we conduct a review on the materials that are used as supports and/or promoters, focusing specifically on the carbon (CNTs, CNFs, and graphene) and metal oxide (Al2O3, MgO, SiO2, and others) materials. Moreover, the reaction mechanism for ammonia decomposition over Ru-based catalysts is described, and future works on designing novel catalysts and unravelling the catalyst structure–activity relationship are proposed.

Characterization of Energy Materials with X-ray Absorption Spectroscopy─Advantages, Challenges, and Opportunities

“…Single-atom catalysts are a common type of active material that has quickly gained popularity. ,,− From an XAS perspective, single-atom catalysts are not a single type of material but can encompass a number of different situations, including those shown in panels c–e of Figure . The popularity of the term “single-atom catalyst” means that some catalysts described a decade ago as sorbed materials (Figure c) and supported coordination compounds (Figure d) are now collectively described as single-atom materials.…”

Hydrogen generation via ammonia decomposition on highly efficient and stable Ru-free catalysts: approaching complete conversion at 450 °C

“…The GHSV was calculated by using the catalytic mass loading (0.1 g) under the flow of pure NH 3 gas (20 mL min À1 ), which was determined to be 12 000 mL h À1 g cat À1 . 17,20,26 Meanwhile, we also used 0.3 g catalyst and the volume-based GHSV, i.e., h À1 , to evaluate catalytic activity, which is more desirable for Ru-free nonprecious metal catalysts, as the amount of Ru-free catalysts is not a concern anymore. The NH 3 conversion efficiency was calculated by using eqn (S1) (ESI †).…”

“…16 Traditionally, ruthenium (Ru) is a well-known metal catalyst for catalyzing the ADR, but its commercial-scale applications are impeded because of its scarcity and high cost. 17 Significant efforts have been made to reduce the cost of catalysts by dispersing Ru nanoparticles (NPs) on various supports, including carbon nanotubes and metal oxides. However, these catalysts still cannot meet the demands of the industry due to the incomplete conversion efficiency at economically feasible temperatures (<450 °C), insufficient stability, and the remaining cost issues.…”

Facile Synthesis and High‐Value Utilization of Ammonia

“…Our group has extensively explored the Ru‐based and Ni‐ based NH 3 decomposition catalysts. [ 36‐38 ] Ru was reported to be the most active metal for ammonia decomposition based on theoretical and experimental researches. [ 39 ] However, current studies on Ru‐based catalysts are of high Ru loading from ca .…”

“…3.0—7.0 wt%, and Ru nanoparticles are prone to agglomerate during long‐ term measurement. [ 38 ] To lower the amount of Ru loading and improve its stability in ammonia decomposition, various supports were applied for supporting Ru in our group, including active metal oxides ( e.g ., CeO 2 and ZrO 2 ) and inert oxide ( e.g ., SiO 2 ). [ 36‐37 ] As displayed in Figure 11a, NH 3 conversions of CeO 2 and ZrO 2 supported Ru catalysts are higher than those of SiO 2 supported ones below 500°C, but beyond 500°C it is quite the reverse.…”