Low‐Valent Manganese Atoms Stabilized on Ceria for Nitrous Oxide Synthesis

Abstract

Nitrous oxide, N2O, exhibits unique reactivity in oxidation catalysis, but the high manufacturing costs limit its prospective uses. Direct oxidation of ammonia, NH3, to N2O can ameliorate this issue but its implementation is thwarted by suboptimal catalyst selectivity and stability, and the lack of established structure–performance relationships. Systematic and controlled material nanostructuring offers an innovative approach for advancement in catalyst design. Herein low‐valent manganese atoms stabilized on ceria, CeO2, are discovered as the first stable catalyst for NH3 oxidation to N2O, exhibiting two‐fold higher productivity than the state‐of‐the‐art. Detailed mechanistic, computational and kinetic studies reveal CeO2 as the mediator of oxygen supply, while undercoordinated manganese species activate O2 and facilitate N2O evolution via NN bond formation between nitroxyl, HNO, intermediates. Synthesis via simple impregnation of a small metal quantity (1 wt%) predominantly generates isolated manganese sites, while full atomic dispersion is achieved upon redispersion of sporadic oxide nanoparticles during reaction, as confirmed by advanced microscopic analysis and electron paramagnetic resonance spectroscopy. Subsequently, manganese speciation is maintained, and no deactivation is observed over 70 h on stream. CeO2‐supported isolated transition metals emerge as a novel class of materials for N2O production, encouraging future studies to evaluate their potential in selective catalytic oxidations at large.

Lattice-Stabilized Chromium Atoms on Ceria for N2O Synthesis

“…The catalytic performance in ammonia oxidation was evaluated at atmospheric pressure in a fixed-bed microreactor (Figure S1). , The gases, He (PanGas, purity 4.6, diluent), NH 3 (PanGas, purity 3.8), O 2 (PanGas, purity 5.0), and Ar (PanGas, purity 5.0, internal standard), were fed using thermal mass-flow controllers (Bronkhorst), connected to a mixing unit equipped with a pressure gauge. The catalyst [particle size = 0.15–0.4 mm, m cat = 0.002–0.2 g for kinetic tests, and 0.05 g for stability tests; for tests at elevated GHSV (>15,000 cm 3 h –1 g cat –1 ) the catalyst bed was diluted with SiC (particle size = 0.5–0.6 mm) to minimize the formation of hot spots] was loaded into a quartz microreactor (inner diameter = 8 mm for m cat > 0.03 g or 2 mm for m cat < 0.03 g), containing a bed made of quartz wool and placed in an electrical oven.…”

“…Instead, propelled by the recent advances in the field of blue and green NH 3 production, direct NH 3 oxidation to N 2 O has emerged as a more efficient and sustainable synthesis method but requires the design of a suitable catalyst. − In this endeavor, manganese oxide-based materials have been most widely investigated, leading to the discovery of a promising Mn–Bi–O/α-Al 2 O 3 system at the Boreskov Institute of Catalysis . Still, issues of suboptimal N 2 O selectivity, catalyst deactivation, and the necessity to work in excess of O 2 , incurring significant downstream costs, have precluded commercialization. , Recently, our group has reported CeO 2 -supported gold nanoparticles and low-valent manganese single atoms as highly efficient catalysts for NH 3 oxidation to N 2 O. , Leveraging the redox properties of CeO 2 has enabled operation under stoichiometric conditions achieving N 2 O selectivity above 80% and 3- to 4-fold higher productivity per gram of catalyst than Mn–Bi–O/α-Al 2 O 3 . This has demonstrated that precise control over the nanostructure of the metal and the properties of the carrier are key to maximizing the catalytic effect , and could be translated to other underexplored materials.…”

“… 17 , 18 Recently, our group has reported CeO 2 -supported gold nanoparticles and low-valent manganese single atoms as highly efficient catalysts for NH 3 oxidation to N 2 O. 19 , 20 Leveraging the redox properties of CeO 2 has enabled operation under stoichiometric conditions achieving N 2 O selectivity above 80% and 3- to 4-fold higher productivity per gram of catalyst than Mn–Bi–O/α-Al 2 O 3 . This has demonstrated that precise control over the nanostructure of the metal and the properties of the carrier are key to maximizing the catalytic effect 21 , 22 and could be translated to other underexplored materials.…”

An Atomically Dispersed Mn-Photocatalyst for Generating Hydrogen Peroxide from Seawater via the Water Oxidation Reaction (WOR)

“…The development of single-atom catalysts (SACs) by dispersing metals onto selected supports, such as zeolites, MOFs, COFs, carbon carriers, oxides, and carbon-nitride, has seen a recent surge in designing efficient heterogeneous catalysts. − This strategy undoubtedly enhances the use of isolated dispersed metal atoms, providing more active sites compared to the corresponding metal clusters and nanoparticle forms. , Practically, it has been proven that, relative to the use of the basic support materials, SACs can enhance the catalytic reactivity and selectivity in specific reactions. − Furthermore, exploiting the advances in X-ray absorption near edge structure (XANES), , extended X-ray absorption fine structure (EXAFS), and solid-state nuclear magnetic resonance (NMR), − a complete picture of the heterogeneous catalytic processes can be provided in some cases. , While metals such as Fe, Ni, Ru, and Pt have been extensively investigated as SACs, other 3d transition metals (from Sc to Mn) have been less explored due to their lower reactivity, even though they are less toxic and expensive. − …”

A COF template-derived mesoporous CeO2-supported Au nanoparticles catalyst for the oxidative esterification of benzaldehydes and benzyl alcohols

“…In particular, in catalytic oxidation reactions, CeO 2 -based catalysts always exhibit superior catalytic performance because of their excellent oxygen storage and release capacity. 27,28 Fabrication of mesoporous CeO 2 supporting materials with a high surface area and mesopores that can strengthen mass transfer during the reaction is still a research challenge.…”