Despite the existence of numerous photocatalyst heterostructures, their separation efficiency and charge flow precision remain low due to the poor study on interfacial properties. The photocatalysts ...with confined defects can effectively control the photogenerated carrier migration, but the metastability of such defects considerably decreases the photocatalyst stability. Meanwhile, the introduction of defective region can increase the coordinative unsaturation and delocalize local electrons to promote their interactions with the molecules/ions in that region. The selective growth of modulated heterogeneous interface by defect‐induced strategy may not only increase the stability of defective structures, but also enhance the migration of interfacial charges. Using this method, photocatalytic heterostructures with low contact resistances and intimate interfaces are constructed to achieve the optimal charge migration in terms of efficiency and accuracy. In this work, the point, linear, and planar heterogeneous interfaces and related defect engineering techniques are discussed. Particularly, it is focused on the external, defect‐induced interfacial heterogeneities with various spatial and dimensional configurations, which exhibit modulated and controllable interfacial properties. Furthermore, the main aspects of fabricating photocatalyst heterostructures by the defect‐induced strategy, including the i) controllable generation of defects, ii) advanced characterization methods, and iii) elaborate construction of the minimal interface, are described.
The heterostructures constructed in the defective areas containing new active sites not only solve the metastability problem of defective structures, but also exhibit unique architectures and spatially modulated properties that preserve their high efficiencies. Eventually, the atomic‐level and modulated interfaces can be customized masterly by regulating defect property, transforming a common interface to a defective interface.
Nanocrystalline Sn-Beta zeolites have been successfully prepared via an improved two-step postsynthesis strategy, which consists of creating vacant T sites with associated silanol groups by ...dealumination of parent H-Beta and subsequent dry impregnation of the resulting Si-Beta with organometallic dimethyltin dichloride. Characterization results from UV–vis, XPS, Raman, and 119Sn solid-state MAS NMR reveal that most Sn species have been successfully incorporated into the framework of Beta zeolite through the postsynthesis process and exist as isolated tetrahedral Sn(IV) in open arrangement. The creation of strong Lewis acid sites upon Sn incorporation is confirmed by FTIR spectroscopy with pyridine adsorption. The Sn-Beta Lewis acid catalysts are applied in the ring-opening hydration of epoxides to the corresponding 1,2-diols under near ambient and solvent-free conditions, and remarkable activity can be obtained. The impacts of Lewis acidity, preparation parameters, and reaction conditions on the catalytic performance of Sn-Beta zeolites are discussed in detail.
Abstract
As a commercial MTO catalyst, SAPO-34 zeolite exhibits excellent recyclability probably due to its intrinsic good hydrothermal stability. However, the structural dynamic changes of SAPO-34 ...catalyst induced by hydrocarbon pool (HP) species and the water formed during the MTO conversion as well as its long-term stability after continuous regenerations are rarely investigated and poorly understood. Herein, the dynamic changes of SAPO-34 framework during the MTO conversion were identified by 1D
27
Al,
31
P MAS NMR, and 2D
31
P-
27
Al HETCOR NMR spectroscopy. The breakage of T-O-T bonds in SAPO-34 catalyst during long-term continuous regenerations in the MTO conversion could be efficiently suppressed by pre-coking. The combination of catalyst pre-coking and water co-feeding is established to be an efficient strategy to promote the catalytic efficiency and long-term stability of SAPO-34 catalysts in the commercial MTO processes, also sheds light on the development of other high stable zeolite catalyst in the commercial catalysis.
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•MoS2/Bi2WO6 nanocomposites (MB) were fabricated by a facile two-step approach.•MoS2 was first used as a cocatalyst coupling with Bi2WO6 for CO2 photoreduction.•MoS2 significantly ...enhanced the photoelectric properties and photoactivity.•The CO32−, HCO3− and H2CO3 in CO2 solution actually act as the reactive substrates.
A novel composite material, MoS2/Bi2WO6, has been fabricated via a facile two-step approach. The few layered MoS2 as a cocatalyst has intimate interactions with the hierarchical flower-like Bi2WO6 microspheres, which boosts the visible light harvesting and charge transferring, and promotes the separation of electron-hole pairs, thus leading to the superior photocatalytic activity. It was found that the as-synthesized MoS2/Bi2WO6 nanocomposites exhibited significantly enhanced performance for the photoreduction of CO2 into hydrocarbons, i.e. methanol and ethanol, as compared with pure Bi2WO6. The yields of methanol and ethanol obtained over the composite with optimal content of MoS2 (0.4wt%) were 36.7 and 36.6μmolgcat−1 after 4h of visible light irradiation, respectively, which were 1.94 times higher than that over pure Bi2WO6. Furthermore, the mechanism of CO2 photoreduction was also investigated. It indicates that the CO32−, HCO3− and H2CO3 generated in CO2 aqueous solution would be the reactive substrates during the photoreduction reaction, proving the thermodynamic feasibility of CO2 photoreduction. This work demonstrated that MoS2 is a very promising candidate for development of highly active photocatalysts, and supplied a facile and simple strategy for designing environmentally benign, cheap non-noble metal, and highly efficient semiconductor composites.
Noble metal nanoparticles or subnanometric particles confined in zeolites, that is, metal@zeolite, represent an important type of functional materials with typical core–shell structure. This type of ...material is known for decades and recently became a research hotspot due to their emerging applications in various fields. Remarkable achievements are made dealing with the synthesis, characterization, and applications of noble metal particles confined in zeolites. Here, the most representative research progress in metal@zeolites is briefly reviewed, aiming to boost further research on this topic. For the synthesis of metal@zeolites, various strategies, such as direct synthesis from inorganic or ligand‐assisted noble metal precursors, multistep postsynthesis encapsulation and ion‐exchange followed by reduction, are introduced and compared. For the characterization of metal@zeolites, several most useful techniques, such as electron microscopy, X‐ray based spectroscopy, infrared and fluorescence emission spectroscopy, are recommended to check the successful confinement of noble metal particles in zeolite matrix and their unique physiochemical properties. For the applications of metal@zeolites, catalysis and optics are involved with an emphasis on catalytic applications including the size‐dependent catalytic properties, the sintering‐resistance properties, the substrate shape‐selective catalysis, and catalysis modulation by zeolite microenvironment.
Noble metal nanoparticles or subnanometric particles confined in zeolites have been known for decades and recently have become a research hotspot due to their emerging applications in various fields. Here, the most representative research progresses on metal@zeolites are briefly reviewed, aiming to boost further research on this topic.
Co3O4@C improved the degradation and conductivity, while SnO2/CC cathode greatly improved the FE and stability of CO2 reduction to HCOOH.
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Herein, we prepared novel three-dimensional ...(3D) gear-shaped Co3O4@C (Co3O4 modified by amorphous carbon) and sheet-like SnO2/CC (SnO2 grow on the carbon cloth) as anode and cathode to achieve efficient removal of 4-nitrophenol (4-NP) in the presence of peroxymonosulfate (PMS) and simultaneous electrocatalytic reduction of CO2, respectively. In this process, 4-NP was mineralized into CO2 by the Co3O4@C, and the generated CO2 was reduced into HCOOH by the sheet-like SnO2/CC cathode. Compared with the pure Co0.5 (Co3O4 was prepared using 0.5 g urea) with PMS (30 mg, 0.5 g/L), the degradation efficiency of 4-NP (60 mL, 10 mg/L) increased from 74.5%–85.1% in 60 min using the Co0.5 modified by amorphous carbon (Co0.5@C). Furthermore, when the voltage of 1.0 V was added in the anodic system of Co0.5@C with PMS (30 mg, 0.5 g/L), the degradation efficiency of 4-NP increased from 85.1%–99.1% when Pt was used as cathode. In the experiments of 4-NP degradation coupled with simultaneous electrocatalytic CO2 reduction, the degradation efficiency of 4-NP was 99.0% in the anodic system of Co0.5@C with addition of PMS (30 mg, 0.5 g/L), while the Faraday efficiency (FE) of HCOOH was 24.1 % at voltage of −1.3 V using the SnO2/CC as cathode. The results showed that the anode of Co3O4 modified by amorphous carbon can markedly improve the degradation efficiency of 4-NP, while the cathode of SnO2/CC can greatly improve the FE and selectivity of CO2 reduction to HCOOH and the stability of cathode. Finally, the promotion mechanism was proposed to explain the degradation of organic pollutants and reduction of CO2 into HCOOH in the process of electrocatalysis coupled with advanced oxidation processes (AOPs) and simultaneous CO2 reduction.
The one-pot conversion of ethanol to butadiene is a promising route for butadiene production; however, simultaneous attainment of high butadiene productivity and high butadiene selectivity is ...challenging. Here, zeolite-confined bicomponent Zn–Y clusters were constructed and applied as robust catalysts for ethanol-to-butadiene conversion with a state-of-the-art butadiene productivity of 2.33 gBD/gcat/h and butadiene selectivity of ∼63%. Structural confinement effects are responsible for the enhanced butadiene production efficiency via a multiple-step cascade reaction.
The development of environmental benign catalysts is the focus on the selective catalytic reduction (SCR) of NO
x
. In this study, a series of SnO
2
-modified MoO
3
nanobelts were fabricated by ...simple impregnation method and applied in the SCR reaction of NO with NH
3
. On these samples, the SnO
2
component disperses evenly on the surface of MoO
3
nanobelts, and some synergistic effect exists between the SnO
2
component and the MoO
3
support. When the content of the loaded SnO
2
was 10 wt%, the obtained 10SnO
2
/MoO
3
catalyst exhibits superior catalytic performance in the SCR reaction. Notably, the SnO
2
/MoO
3
catalysts possess great resistance for SO
2
and H
2
O in the reaction as well. The modification of SnO
2
could significantly promote the redox property, increase the surface acid sites and the surface chemisorbed oxygen species of the catalysts, which were key factor for the good NH
3
-SCR catalytic performance of the SnO
2
/MoO
3
catalysts.
Graphic Abstract
The SnO
2
-modifation could improve the acid sites and redox property of the MoO
3
, thus enhancing its catalytic performance in the NH
3
-SCR reaction of NO.
Ga-modified nano H-ZSM-5 zeolites with different Ga contents were prepared and applied as methanol-to-aromatics (MTA) catalysts. The Ga introduction can strongly increase the selectivity to aromatics ...but also decrease the catalyst lifetime simultaneously. Upon the cofeeding of n-butanol with methanol, a significant prolongation of the catalyst lifetime from 18 to ca. 50 h can be achieved. According to several spectroscopic results, e.g., TGA, GC–MS, in situ UV/vis, and solid-state MAS NMR spectroscopy, the addition of n-butanol during the MTA conversion shows no impact on the deactivation mechanism but can influence the dual-cycle mechanism. Namely, n-butanol preferentially adsorbs on Brønsted acid sites over methanol, followed by dehydration into n-butene. The formed n-butene can directly participate in the olefin-based cycle and, therefore, significantly alter the proportions of the dual-cycle mechanism. These results provide mechanistic insights into the roles of n-butanol cofeeding in the MTA conversion and exemplify a simple but efficient strategy to prolonged the catalyst lifetime, which is crucial to the industrial application.
Coverage of active sites by large unsaturated aldehydes/ketones transformed from the intermediate acetaldehyde and by-product acetone responsible for catalyst deactivation in ethanol-to-butadiene ...conversion.
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•Deactivation mechanism of Zn-Y/Beta catalyst in ethanol-to-butadiene conversion investigated by complementary approaches.•Both the intermediate acetaldehyde and by-product acetone participate in the aldol condensation.•Large unsaturated aldehydes/ketones formed from condensation and cyclization reactions.•Coverage of active sites by large unsaturated aldehydes/ketones responsible for the catalyst deactivation.
Despite of extensive attention on the ethanol to butadiene (ETB) conversion, the catalyst deactivation during ETB conversion is rarely investigated and poorly understood. Here, the mechanism of the catalyst deactivation during the ETB conversion over Zn-Y/Beta was investigated through several complementary approaches, including XPS, TGA, GC–MS, in situ DRIFTS, UV–vis and 13C CP MAS NMR spectroscopy. Acetaldehyde was observed to be the first reactive intermediate formed in the ETB conversion, which was rapidly involved in a subsequent aldol condensation with the simultaneous production of acetone. Due to a self- and cross-condensation of acetaldehyde and acetone, long chain unsaturated aldehydes/ketones were formed and further converted to 2,4-dimethyl benzaldehyde via a cyclization reaction, which could gradually cover the active sites and led to catalyst deactivation. Fortunately, the deactivating species could be removed from catalyst surface via simple calcination and the complete regeneration of Zn-Y/Beta could be realized.
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