Insight into rare-earth-incorporated catalysts: The chance for a more efficient ammonia synthesis

Abstract

Recent studies have suggested that rare earth (RE) elements in catalysts significantly influence the performance of the ammonia synthesis. The REs appear in various forms in the ammonia synthesis catalysts including supports (oxides, hydrides, and nitrides), promotors, and intermetallic. Besides the conventional RE oxide-supporting catalysts (mainly Ru/REO), some new RE-containing catalyst systems, such as electrode and nitride systems, could drive the ammonia synthesis via a benign Mars—van Krevelen mechanism or multi-active-site mode, affording high ammonia synthesis performance under mild conditions. These works demonstrate the great potential of RE-containing catalysts for more efficient ammonia synthesis. This review summarizes the contributions of different kinds of RE-based catalysts and highlights the function mechanism of incorporated REs. Finally, an overview of this area and the challenges for further investigation are provided.

Influence of the Rare Earth (R) Element in Ru‐supportedRScSi Electride‐like Intermetallic Catalysts for Ammonia Synthesis at Low Pressure: Insight into NH3Formation Mechanism

“…[17] However, a systematic study of the impact of the rare earth element (R) in RScSi ternary intermetallics for the catalytic Haber-Bosch synthesis is still lacking. In fact, Gong et al [18] recently noted the great potential of rare earth-containing catalysts for more efficient ammonia synthesis. In addition, ammonia production at the laboratory scale is usually monitored under steady-state conditions of temperature, by ammonia trapping in a sulphuric acid solution and subsequent analysis by ion chromatography.…”

Potential Future Alternative Resources for Rare Earth Elements: Opportunities and Challenges

“…REE are vital even to the space industry as they are used in everything from launch vehicles to national defence and commercial communications and observation satellites. REE are also used in making catalysts in several industrial processes as well as in the fabrication of autocatalytic catalytic converters in transport vehicles [5,6]. Although REE deposits are found practically in all parts of the world, currently there is a global shortage, due to the decreasing number of economically profitable deposits.…”

CeNix Alloys as Catalysts for Ammonia Synthesis: Insights on Ni–CeN Surface Layer Formation and Its Impact

“…RE elements have attracted significant attention in the field of ammonia synthesis at mild conditions. 17 Their versatile chemical nature allows them to generate different active centers, thereby facilitating the dispersion of TMs on their surface. In the case of RE oxides, the high reducibility of these materials results in the formation of surface oxygen vacancies upon reduction, promoting the so-called strong metal−support interaction (SMSI).…”

“…RE elements have attracted significant attention in the field of ammonia synthesis at mild conditions . Their versatile chemical nature allows them to generate different active centers, thereby facilitating the dispersion of TMs on their surface.…”

“…In the case of RE oxides, the high reducibility of these materials results in the formation of surface oxygen vacancies upon reduction, promoting the so-called strong metal–support interaction (SMSI). The formation of these oxygen vacancies improves the dispersion of the TM while promoting electron transfer processes toward the metal, thereby facilitating the activation and dissociation of the N 2 molecule. , This strategy has demonstrated to be useful for metals with optimum nitrogen absorption energy, such as Ru , or Co . RE hydrides and oxyhydrides have shown higher activities compared to RE oxides since the highly mobile H – further enhances the electron donation process. , In general, the use of a suitable material as a secondary active center has been demonstrated to boost the activity of TMs with optimum nitrogen absorption energies.…”