Zeolite‐Encaged Single‐Atom Rhodium Catalysts: Highly‐Efficient Hydrogen Generation and Shape‐Selective Tandem Hydrogenation of Nitroarenes

Abstract

Single‐atom catalysts are emerging as a new frontier in heterogeneous catalysis because of their maximum atom utilization efficiency, but they usually suffer from inferior stability. Herein, we synthesized single‐atom Rh catalysts embedded in MFI‐type zeolites under hydrothermal conditions and subsequent ligand‐protected direct H2 reduction. Cs‐corrected scanning transmission electron microscopy and extended X‐ray absorption analyses revealed that single Rh atoms were encapsulated within 5‐membered rings and stabilized by zeolite framework oxygen atoms. The resultant catalysts exhibited excellent H2 generation rates from ammonia borane (AB) hydrolysis, up to 699 min−1 at 298 K, representing the top level among heterogeneous catalysts for AB hydrolysis. The catalysts also showed superior catalytic performance in shape‐selective tandem hydrogenation of various nitroarenes by coupling with AB hydrolysis, giving >99 % yield of corresponding amine products.

Commercially Available CuO Catalyzed Hydrogenation of Nitroarenes Using Ammonia Borane as a Hydrogen Source

“…[27][28][29][30][31][32][33][34][35][36][37][38][39] Multiple reports have described nanoparticle-type catalysts that exhibit good activity, selectivity, and reusability for hydrogenation reactions; however, most of these are composed of at least two types of transition metals, [27][28][29][30][31][32] and even noble metals. [30][31][32][33][34]38,39] In general, these ultra-small metal nanoparticles are loaded onto special solid supports, such as graphene, [28,29] MOFs, [30] reduced graphene oxide, [31] nitrogen-doped graphene, [32] TiO 2 , [34] or N-doped porous carbon. [35] For example, Sun and co-workers reported the chemoselective reduction of 3-nitrostyrene to 3-vinylaniline within 1.5 h using exquisitely designed Cu nanoparticles anchored on WO 2.72 nanorods.…”

“…Having established the optimized reaction conditions, we next investigated the substrate scope of this transformation to probe the generality and limitations of the reaction (Scheme 2). Various electron-donating groups, including Me (2, 3), iPr (4), NH 2 (6-8), MeO (9, 10), OH (20, 21, 27), MeS (22), and CH 2 OH (38), and electron-withdrawing substituents, such as halogens (11)(12)(13)(14), CF 3 (16,17), and CO 2 Me (26), were compatible with the reaction system, delivering the aniline products in excellent yields. This hydrogenation proved to be insensitive towards steric encumbrance in the vicinity of the targeted nitro group (1-4, 6-8).…”

Sustainable Hydrogenation of Nitroarenes to Anilines with Highly Active In-Situ Generated Copper Nanoparticles

“…By the hydrolysis of AB, hydrogen release occurs at room temperature and under ambient pressure, eliminating the safety issues and the poor solubility problem of H 2 gas in water. [16] We demonstrated that after the hydrogen generation from AB is complete, fresh and highly crystalline mineral microcrystals are regenerated from Cu 0 NPs in a quantitative yield. Therefore, AB hydrolysis was performed for at least 10 cycles with a negligible decrease of the catalyst's activity.…”

Nanopore‐Supported Metal Nanocatalysts for Efficient Hydrogen Generation from Liquid‐Phase Chemical Hydrogen Storage Materials

“…Nanoporous materials with abundant nanopores and/or cavities are ideal hosts to encapsulate ultrafine metal species inside their nanoporous matrices against sintering. [11] In recent years, nanoporous materials, such as microporous zeolites, [12] metal-organic frameworks (MOFs), [13] mesoporous silica, [14] porous carbon, [15] porous organic cages (POC), [16] and porous onto these porous materials, which further enhance the stability of immobilized metal species, modify the nanostructure of metal active sites, and improve the catalytic activity. [18] Notably, the inherent acidity and basicity of some porous supports integrated with metal species can also promote the catalytic performance.…”