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Amine-containing solids have been investigated as promising adsorbents for CO 2 capture, but the low oxidative stability of amines has been the biggest hurdle for their practical applications. Here, we developed an extra-stable adsorbent by combining two strategies. First, poly(ethyleneimine) (PEI) was functionalized with 1,2-epoxybutane, which generates tethered 2-hydroxybutyl groups. Second, chelators were pre-supported onto a silica support to poison p.p.m.-level metal impurities (Fe and Cu) that catalyse amine oxidation. The combination of these strategies led to remarkable synergy, and the resultant adsorbent showed a minor loss of CO 2 working capacity (8.5%) even after 30 days aging in O 2 -containing flue gas at 110 °C. This corresponds to a ~50 times slower deactivation rate than a conventional PEI/silica, which shows a complete loss of CO 2 uptake capacity after the same treatment. The unprecedentedly high oxidative stability may represent an important breakthrough for the commercial implementation of these adsorbents. Amine-containing solids are promising adsorbents for CO 2 capture, but their low oxidative stability has hindered their application. Here, Choi and colleagues develop a strategy to poison the metal impurities present in poly(ethyleneimine)/silica adsorbents, significantly improving their stability towards oxidation.

Maximum atom efficiency as well as distinct chemoselectivity is expected for electrocatalysis on atomically dispersed (or single site) metal centres, but its realization remains challenging so far, because carbon, as the most widely used electrocatalyst support, cannot effectively stabilize them. Here we report that a sulfur-doped zeolite-templated carbon, simultaneously exhibiting large sulfur content (17 wt% S), as well as a unique carbon structure (that is, highly curved three-dimensional networks of graphene nanoribbons), can stabilize a relatively high loading of platinum (5 wt%) in the form of highly dispersed species including site isolated atoms. In the oxygen reduction reaction, this catalyst does not follow a conventional four-electron pathway producing H 2 O, but selectively produces H 2 O 2 even over extended times without significant degradation of the activity. Thus, this approach constitutes a potentially promising route for producing important fine chemical H 2 O 2 , and also offers opportunities for tuning the selectivity of other electrochemical reactions on various metal catalysts. Atomically dispersed metal catalysts display high atom efficiency for electrocatalytic processes. Here, the authors report that sulfur-doped zeolite-templated carbon stabilizes highly dispersed platinum species, predominantly as single-atom centres, and probe its oxygen reduction selectivity.

Amine-containing adsorbents have been extensively investigated for post-combustion carbon dioxide capture due to their ability to chemisorb low-concentration carbon dioxide from a wet flue gas. However, earlier studies have focused primarily on the carbon dioxide uptake of adsorbents, and have not demonstrated effective adsorbent regeneration and long-term stability under such conditions. Here, we report the versatile and scalable synthesis of a functionalized-polyethyleneimine (PEI)/silica adsorbent which simultaneously exhibits a large working capacity (2.2 mmol g −1 ) and long-term stability in a practical temperature swing adsorption process (regeneration under 100% carbon dioxide at 120 °C), enabling the separation of concentrated carbon dioxide. We demonstrate that the functionalization of PEI with 1,2-epoxybutane reduces the heat of adsorption and facilitates carbon dioxide desorption (>99%) during regeneration compared with unmodified PEI (76%). Moreover, the functionalization significantly improves long-term adsorbent stability over repeated temperature swing adsorption cycles due to the suppression of urea formation and oxidative amine degradation. Carbon dioxide capture technologies have been implemented as a strategy to alleviate the environmental costs of CO 2 emissions. Here, the authors synthesize a functionalized-polyethyleneimine/silica adsorbent for post-combustion CO 2 capture that exhibits a large CO 2 capacity and long-term stability.

Metal promotion is the most widely adopted strategy for enhancing the hydrogenation functionality of an oxide catalyst. Typically, metal nanoparticles or dopants are located directly on the catalyst surface to create interfacial synergy with active sites on the oxide, but the enhancement effect may be compromised by insufficient hydrogen delivery to these sites. Here, we introduce a strategy to promote a ZnZrO x methanol synthesis catalyst by incorporating hydrogen activation and delivery functions through optimized integration of ZnZrO x and Pd supported on carbon nanotube (Pd/CNT). The CNT in the Pd/CNT + ZnZrO x system delivers hydrogen activated on Pd to a broad area on the ZnZrO x surface, with an enhancement factor of 10 compared to the conventional Pd-promoted ZnZrO x catalyst, which only transfers hydrogen to Pd-adjacent sites. In CO 2 hydrogenation to methanol, Pd/CNT + ZnZrO x exhibits drastically boosted activity—the highest among reported ZnZrO x -based catalysts—and excellent stability over 600 h on stream test, showing potential for practical implementation. Boosting activity of oxide catalysts is a long-lasting challenge to developing efficient catalysts for industrially important reactions such as CO 2 -to-methanol. Here, the authors report a strategy for enhancing the activity of a ZnZrO x methanol synthesis catalyst via engineered nanoscale H supply.

Hydrogen spillover has been studied for several decades, but its nature, catalytic functions and even its existence remain topics of vigorous debate. This is a consequence of the lack of model catalysts that can provide direct evidences of the existence of hydrogen spillover and simplify the catalytic interpretation. Here we use platinum encapsulated in a dense aluminosilicate matrix with controlled diffusional properties and surface hydroxyl concentrations to elucidate the catalytic functions of hydrogen spillover. The catalytic investigation and theoretical modelling show that surface hydroxyls, presumably Brønsted acids, are crucial for utilizing the catalytic functions of hydrogen spillover on the aluminosilicate surface. The catalysts with optimized nanostructure show remarkable activities in hydro-/dehydrogenation, but virtually no activity for hydrogenolysis. This distinct chemoselectivity may be beneficial in industrially important hydroconversions such as propane dehydrogenation to propylene because the undesired hydrogenolysis pathway producing light hydrocarbons of low value (methane and ethane) is greatly suppressed. The hydrogen spillover mechanism has been studied for several decades, although its exact elucidation has been hampered by the lack of suitable model catalyst systems. Here, the authors combine experimental and computational techniques to probe the role of surface hydroxyls in the mechanism.

Metal promotion is the most widely adopted strategy for enhancing the hydrogenation functionality of an oxide catalyst. Typically, metal nanoparticles or dopants are located directly on the catalyst surface to create interfacial synergy with active sites on the oxide, but the enhancement effect may be compromised by insufficient hydrogen delivery to these sites. Here, we introduce a strategy to promote a ZnZrO methanol synthesis catalyst by incorporating hydrogen activation and delivery functions through optimized integration of ZnZrO and Pd supported on carbon nanotube (Pd/CNT). The CNT in the Pd/CNT + ZnZrO system delivers hydrogen activated on Pd to a broad area on the ZnZrO surface, with an enhancement factor of 10 compared to the conventional Pd-promoted ZnZrO catalyst, which only transfers hydrogen to Pd-adjacent sites. In CO hydrogenation to methanol, Pd/CNT + ZnZrO exhibits drastically boosted activity-the highest among reported ZnZrO -based catalysts-and excellent stability over 600 h on stream test, showing potential for practical implementation.

Zeolite catalysis: the thin of it Zeolites — microporous crystalline aluminosilicates — are widely used in industry as size- and shape-selective catalysts. But the very micropores that make this catalytic activity possible also cause diffusion limitations. Choi et al . now show that the problem can be overcome by synthesizing zeolites in the presence of bifunctional surfactants, which simultaneously direct the formation of micropores and limit the growth of the zeolite crystal to that of a 'nanosheet' with a thickness of only one unit cell. These structural features render the ultrathin zeolites highly active for the catalytic conversion of large organic molecules; they also minimize the adverse effects of diffusion limitations, as illustrated by drastically reduced coke deposition and catalyst deactivation during methanol-to-gasoline conversion. Zeolites — microporous crystalline aluminosilicates — are widely used in industry as size- and shape-selective catalysts, but the micropores that enable this catalytic activity also cause diffusion limitations that adversely affect it. This can be overcome by reducing the thickness of the zeolite crystals and thus improving molecular diffusion. Here it is shown that bifunctional surfactants can direct the formation of zeolite structures that are only one unit cell thick. Zeolites—microporous crystalline aluminosilicates—are widely used in petrochemistry and fine-chemical synthesis 1 , 2 , 3 because strong acid sites within their uniform micropores enable size- and shape-selective catalysis. But the very presence of the micropores, with aperture diameters below 1 nm, often goes hand-in-hand with diffusion limitations 3 , 4 , 5 that adversely affect catalytic activity. The problem can be overcome by reducing the thickness of the zeolite crystals, which reduces diffusion path lengths and thus improves molecular diffusion 4 , 5 . This has been realized by synthesizing zeolite nanocrystals 6 , by exfoliating layered zeolites 7 , 8 , 9 , and by introducing mesopores in the microporous material through templating strategies 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 or demetallation processes 18 , 19 , 20 , 21 , 22 . But except for the exfoliation, none of these strategies has produced ‘ultrathin’ zeolites with thicknesses below 5 nm. Here we show that appropriately designed bifunctional surfactants can direct the formation of zeolite structures on the mesoporous and microporous length scales simultaneously and thus yield MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolite nanosheets that are only 2 nm thick, which corresponds to the b -axis dimension of a single MFI unit cell. The large number of acid sites on the external surface of these zeolites renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-to-gasoline conversion. We expect that our synthesis approach could be applied to other zeolites to improve their performance in a range of important catalytic applications.

Hydrogen (H) spillover in nonreducible oxides such as zeolites and Al 2 O 3 has been a highly controversial phenomenon in heterogeneous catalysis. Since industrial catalysts are predominantly prepared using these materials as supports, it is important to understand the mechanism and catalytic functions of H spillover on their surfaces. In the past decade, fundamental studies on zeolite-encapsulated metal catalysts have revealed that H spillover and reverse spillover can be utilized in the design of hydrogenation and dehydrogenation catalysts with improved properties. Both experimental and theoretical studies have indicated that H spillover can occur in nonreducible oxides when they possess substantial acid sites that aid the surface migration of active H. In the present review, we will discuss the possible mechanisms of H spillover in nonreducible oxides and the unique opportunities of using this phenomenon for the design of advanced hydroprocessing catalysts.

Zeolites are a family of crystalline aluminosilicate materials widely used as shape-selective catalysts, ion exchange materials, and adsorbents for organic compounds 1 , 2 . In the present work, zeolites were synthesized by adding a rationally designed amphiphilic organosilane surfactant to conventional alkaline zeolite synthesis mixtures. The zeolite products were characterized by a complementary combination of X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The analyses show that the present method is suitable as a direct synthesis route to highly mesoporous zeolites. The mesopore diameters could be uniformly tailored, similar to ordered mesoporous silica with amorphous frameworks 3 . The mesoporous zeolite exhibited a narrow, small-angle XRD peak, which is characteristic of the short-range correlation between mesopores, similar to disordered wormhole-like mesoporous materials 4 , 5 . The XRD patterns and electron micrographs of the samples taken during crystallization clearly showed the evolution of the mesoporous structure concomitantly to the crystallization of zeolite frameworks. The synthesis of the crystalline aluminosilicate materials with tunable mesoporosity and strong acidity has potentially important technological implications for catalytic reactions of large molecules, whereas conventional mesoporous materials lack hydrothermal stability and acidity.

NaA zeolite (Si/Al = 1.00) has been commercially applied for capturing radioactive 90Sr 2+ because of its high surface charge density, effectively stabilizing the multivalent cation. However, owing to its narrow micropore opening (4.0 Å), large micron-sized crystallites, and bulkiness of hydrated Sr 2+, the Sr 2+ exchange over NaA has been limited by very slow kinetics. In this study, we synthesized nanocrystalline low-silica X by minimizing a water content in a synthesis gel and utilizing a methyl cellulose hydrogel as a crystal growth inhibitor. The resulting zeolite exhibited high crystallinity and Al-rich framework (Si/Al of approximately 1.00) with the sole presence of tetrahedral Al sites, which are capable of high Sr 2+ uptake and ion selectivity. Meanwhile, the zeolite with a FAU topology has a much larger micropore opening size (7.4 Å) and a much smaller crystallite size (~340 nm) than NaA, which enable significantly enhanced ion-exchange kinetics. Compared to conventional NaA, the nanocrystalline low-silica X exhibited remarkably increased Sr 2+-exchange kinetics (> 18-fold larger rate constant) in batch experiments. Although both the nanocrystalline low-silica X and NaA exhibited comparable Sr 2+ capacities under equilibrated conditions, the former demonstrated a 5.5-fold larger breakthrough volume than NaA under dynamic conditions, attributed to its significantly faster Sr 2+-exchange kinetics.