Selectivity Of Target Product Research Articles

The Effect of Crown Ethers and Polyglycols on the Sustainability Indicators of Cyclohexane Oxidation Process

The crown ether or polyglycol additives to transition metal catalysts improve both the performance indicators, such as cyclohexane conversion, selectivity of target products, and the sustainability indicators of the oxidation process. It has been shown that the effect of the organic additives on the sustainability indicators is primarily due to a significant (up to 14.3%) increase in the selectivity of target cyclohexane oxidation products.

A Green and Efficient Electrocatalytic Route for the Highly‐Selective Oxidation of C–H Bonds in Aromatics over 1D Co3O4‐Based Nanoarrays

Electrocatalytic oxidation of C‐H bonds in hydrocarbons represents an efficient and sustainable strategy for the synthesis of value‐added chemicals. Herein, a highly selective and continuous‐flow electrochemical oxidation process of toluene to various oxygenated products (benzyl alcohol, benzaldehyde, and benzyl acetate) is developed with the electrocatalytic membrane electrodes (ECMEs). The selectivity of target products can be manipulated via surface and interface engineering of Co3O4‐based electrocatalysts. We achieved a high benzaldehyde selectivity of 90% at a toluene conversion of 47.6% using 1D‐Co3O4 nanoneedles (NNs) loaded on a microfiltration (MF) titanium (Ti) membrane, i.e, Co3O4 NNs/Ti. In contrast, the main product shifted to benzyl alcohol with a selectivity of 90.1% at conversion of 32.1% after modifying MnO2 nanosheets (NSs) on Co3O4 NNs/Ti (Co3O4@MnO2/Ti) catalyst. Moreover, benzyl acetate product can be obtained with selectivity of 92% at a conversion of 58.5% at high current density (> 1.5mA cm‐2), demonstrating that the pathway of toluene oxidation is readily maneuvered. DFT results reveal that modifying MnO2 on Co3O4 optimizes the electron structure of Co3O4@MnO2/Ti and modulates the adsorption behavior of intermediate species. This work demonstrates a sustainable, and continuous‐flow process for precise control over production selectivity of value‐added oxygenated derivatives in electrochemical oxidation of aromatic hydrocarbons.

A Green and Efficient Electrocatalytic Route for the Highly-Selective Oxidation of C-H Bonds in Aromatics over 1D Co3O4-Based Nanoarrays.

Electrocatalytic oxidation of C-H bonds in hydrocarbons represents an efficient and sustainable strategy for the synthesis of value-added chemicals. Herein, a highly selective and continuous-flow electrochemical oxidation process of toluene to various oxygenated products (benzyl alcohol, benzaldehyde, and benzyl acetate) is developed with the electrocatalytic membrane electrodes (ECMEs). The selectivity of target products can be manipulated via surface and interface engineering of Co3O4-based electrocatalysts. We achieved a high benzaldehyde selectivity of 90% at a toluene conversion of 47.6% using 1D-Co3O4 nanoneedles (NNs) loaded on a microfiltration (MF) titanium (Ti) membrane, i.e, Co3O4 NNs/Ti. In contrast, the main product shifted to benzyl alcohol with a selectivity of 90.1% at conversion of 32.1% after modifying MnO2 nanosheets (NSs) on Co3O4 NNs/Ti (Co3O4@MnO2/Ti) catalyst. Moreover, benzyl acetate product can be obtained withselectivity of 92% at a conversion of 58.5% at high current density (> 1.5mA cm-2), demonstrating that the pathway of toluene oxidation is readily maneuvered. DFT results reveal that modifying MnO2 on Co3O4 optimizes the electron structure of Co3O4@MnO2/Ti and modulates the adsorption behavior of intermediate species. This work demonstrates a sustainable,and continuous-flow process for precise control over production selectivity of value-added oxygenated derivatives in electrochemical oxidation of aromatic hydrocarbons.

An acid-tolerant metal-organic framework for industrial CO2 electrolysis using a proton exchange membrane

Industrial CO2 electrolysis via electrochemical CO2 reduction has achieved progress in alkaline solutions, while the same reaction in acidic solution remains challenging because of severe hydrogen evolution side reactions, acid corrosion, and low target product selectivity. Herein, an industrial acidic CO2 electrolysis to pure HCOOH system is realized in a proton-exchange-membrane electrolyzer using an acid-tolerant Bi-based metal-organic framework guided by a Pourbaix diagram. Significantly, the Faradaic efficiency of HCOOH synthesis reaches 95.10% at a large current density of 400 mA/cm2 with a high CO2 single-pass conversion efficiency of 64.91%. Moreover, the proton-exchange-membrane device also achieves an industrial-level current density of 250 mA/cm2 under a relatively low voltage of 3.5 V for up to 100 h with a Faradaic efficiency of 93.5% for HCOOH production, which corresponds to an energy consumption of 200.65 kWh/kmol, production rate of 12.1 mmol/m2/s, and an energy conversion efficiency of 38.2%. These results will greatly aid the contemporary research moving toward commercial implementation and success of CO2 electrolysis technology.

Significant Promotional Effect of Nb Doping in Bifunctional Pd/WOx Nanocatalysts on One‐Step Benzene Hydroalkylation

AbstractThe development of high‐efficiency heterogeneous bifunctional metal‐acid catalysts with an appropriate metal‐acid balance for the production of cyclohexylbenzene (CHB) via the one‐step tandem benzene hydroalkylation still faces a dilemma because of the difficulty in inhibiting the over hydrogenation of benzene substrate and cyclohexene intermediate and controlling target product selectivity. In this study, Nb‐doped WOx supported Pd nanocatalysts were developed. It has been shown that doping Nb into WOx supports altered surface properties and microstructures of catalysts, resulting in the generation of more surface acidic sites and defective W−Ov−Nb structures (Ov: oxygen vacancies). As‐constructed Pd‐based nanocatalyst with only 0.1 wt % Pd loading and a Nb/(Nb+W) molar ratio of 0.25 exhibited superior catalytic benzene hydroalkylation performance to undoped supported Pd catalyst, with a much higher yield of CHB (35.6 %) at 220 °C. It was authenticated that highly dispersed Pd sites facilitated the dissociation of hydrogen molecules, defective W−Ov−Nb structures were conductive to the surface transfer of active hydrogen species, a large number of acidic sites favored benzene/cyclohexene intermediate adsorption, and abundant Brønsted acidic sites promoted the alkylation between cyclohexene intermediate formed and benzene. Accordingly, excellent cooperative catalysis between Pd sites, acidic sites, and oxygen vacancies contributed to improved catalytic performance of Nb‐doped WOx supported Pd catalysts in benzene hydroalkylation. This research presents an alternative for the creation of low‐cost practical bifunctional metal‐acid catalysts for highly efficient benzene hydroalkylation.

Improved Lignin Conversion to High-Value Aromatic Monomers through Phase Junction CdS with Coexposed Hexagonal (100) and Cubic (220) Facets.

Photocatalysis has the potential for lignin valorization to generate functionalized aromatic monomers, but its application has been limited by the slow conversion rate and the low selectivity to desirable aromatic products. In this work, we designed the phase junction CdS with coexposed hexagonal (100) and cubic (220) facets to improve the photogenerated charge carriers' transfer efficiency from (100) facet to (220) facet and the hydrogen transfer efficiency for an enhanced conversion rate of lignin to aromatic monomers. Water is found as a sufficient external hydrogen supplier to increase the yields of aromatic monomers. These innovative designs in the reaction system promoted complete conversion of PP-ol to around 94% of aromatic monomers after 1 h of visible light irradiation, which shows the highest reaction rate and selectivity of target products in comparison with previous works. PP-one is a byproduct from the overoxidation of PP-ol and is usually difficult to be further cleaved to acetophenone and phenol as the desirable aromatic monomers. TEA was first identified in this study as a sacrificial electron donor, a hydrogen source, and a mediator to enhance the cleavage of the Cβ-O bonds in PP-one. With the assistance of TEA, PP-one can be completely cleaved to desirable aromatic monomer products, and the reaction time is reduced from several hours to 10 min of visible light irradiation.

Complete Degradation of Polyolefin Plastic Wastes to High-Value Products.

Plastic wastes continuously accumulate, causing critical environmental issues. It is urgent to develop efficient strategies to convert them to valuable products. Very recently, two novel approaches for plastic recycling were reported by Huber et al. (Science, 2023, 381, 660-666) and Liu et al. (Science, 2023, 381, 666-671), where polyethylene (PE) and polypropylene (PP) plastics were converted into potentially valuable products, such as alcohols, aldehydes, surfactants, and detergents. The two processes achieved complete degradation, high selectivity of target products, as well as high values of products, showing economic feasibility for industrial scale-up. These breakthroughs for plastic recycling are highlighted in this article.

Highly efficient selective hydrogenation of adiponitrile to hexamethylene diamine over barium and melamine formaldehyde resin-modified nickel–cobalt-based zeolitic imidazolate framework-derived catalyst

In the present study, the catalyst modified with alkaline oxide can enhance the selectivity to primary amines. However, the addition of alkaline oxide inevitably reduces catalytic activity. In this study, NiCo-NC@BaO-MFC catalyst derived from zeolitic imidazolate framework-67, Ba(CH3COO)2, and melamine formaldehyde (MF) resin was prepared and used for the hydrogenation of adiponitrile (ADN) to hexamethylene diamine (HDMA). The carbon layer obtained from the MF resin effectively prevents the interaction between barium (Ba) and the active center, thus improving target product selectivity without decreasing catalytic activity. The results of the density functional theory (DFT) calculation and characterization indicated that the effect of synergy between nickel (Ni) and cobalt (Co) bimetals induces an electron density growth on the Ni surface, bringing the d-band center toward the Fermi surface. Meanwhile, the high electron density of the active center compensates for the electron-deficient state of the carbon atom in –CN, thus improving the catalytic activity. Furthermore, it was found that the introduction of Ba promotes the formation of nucleophilic hydrogen anions, which facilitates the hydrogenation of 6-aminohexylimine (AHIM) to HDMA and inhibits the intramolecular condensation of AHIM, hence improving the selectivity to HDMA. The NiCo-NC@BaO-MFC catalyst gives 98.6 % ADN conversion and 97.2 % selectivity to HDMA in an alkali-free system.

Breaking the Activity-Selectivity Trade-off for CH4-to-C2H6 Photoconversion.

Photocatalytic conversion of methane (CH4) to ethane (C2H6) has attracted extensive attention from academia and industry. Typically, the traditional oxidative coupling of CH4 (OCM) reaches a high C2H6 productivity, yet the inevitable overoxidation limits the target product selectivity. Although the traditional nonoxidative coupling of CH4 (NOCM) can improve the product selectivity, it still encounters unsatisfied activity, arising from being thermodynamically unfavorable. To break the activity-selectivity trade-off, we propose a conceptually new mechanism of H2O2-triggered CH4 coupling, where the H2O2-derived ·OH radicals are rapidly consumed for activating CH4 into ·CH3 radicals exothermically, which bypasses the endothermic steps of the direct CH4 activation by photoholes and the interaction between ·CH3 and ·OH radicals, affirmed by in situ characterization techniques, femtosecond transient absorption spectroscopy, and density-functional theory calculation. By this pathway, the designed Au-WO3 nanosheets achieve unprecedented C2H6 productivity of 76.3 mol molAu-1 h-1 with 95.2% selectivity, and TON of 1542.7 (TOF = 77.1 h-1) in a self-designed flow reactor, outperforming previously reported photocatalysts regardless of OCM and NOCM pathways. Also, under outdoor natural sunlight irradiation, the Au-WO3 nanosheets exhibit similar activity and selectivity toward C2H6 production, showing the possibility for practical applications. Interestingly, this strategy can be applied to other various photocatalysts (Au-WO3, Au-TiO2, Au-CeO2, Pd-WO3, and Ag-WO3), showing a certain universality. It is expected that the proposed mechanism adds another layer to our understanding of CH4-to-C2H6 conversion.

Towards Sustainable H2O2 Photogeneration: Advancements, Challenges, and Future Prospects

AbstractHydrogen peroxide (H2O2) has emerged as a versatile and environmentally friendly oxidant, showing wide applications in diverse sectors such as fine chemical synthesis, waste stream treatment, precious metal extraction, and textile bleaching. With an escalating demand, H2O2 has now become one of the most essential chemicals worldwide. Efficient photocatalytic generation of H2O2 from water (H2O) and oxygen (O2) has been a long‐standing challenge, presenting a promising prospect to replace existing production methods. This review presents a framework aimed at achieving highly efficient and continuous H2O2 production via photocatalysis. The key aspects include photocatalyst design, selectivity for redox reactions, stability issue and reactor design. Through a comprehensive inspection and comparison of state‐of‐the‐art research, the most viable pathways for H2O2 photogeneration are identified, ensuring optimal solar‐to‐fuel conversion efficiency and high selectivity for target products. The ultimate goal is to establish H2O2 photogeneration as a sustainable and efficient method for producing this valuable chemical, contributing to a greener and more sustainable future.

Atomically dispersed Cu coordinated Rh metallene arrays for simultaneously electrochemical aniline synthesis and biomass upgrading

Organic electrocatalytic conversion is an essential pathway for the green conversion of low-cost organic compounds to high-value chemicals, which urgently demands the development of efficient electrocatalysts. Here, we report a Cu single-atom dispersed Rh metallene arrays on Cu foam for cathodic nitrobenzene electroreduction reaction and anodic methanol oxidation reaction. In the coupled electrocatalytic system, the Cusingle-atom-Rh metallene arrays on Cu foam requires only the low voltages of 1.18 V to reach current densities of 100 mA cm−2 for generating aniline and formate, with up to ~100% of nitrobenzene conversion/ aniline selectivity and over ~90% of formate Faraday efficiency, achieving synthesis of high-value chemicals. Density functional theory calculations reveal the electron effect between Cu single-atom and Rh host and catalytic reaction mechanism. The synergistic catalytic effect and H*-spillover effect can improve catalytic reaction process and reduce energy barrier for reaction process, thus enhancing electrocatalytic reaction activity and target product selectivity.

HBEA/MTW composite molecular sieves with shape-selectively catalyzed alkylation of 2-methylnaphthalene with methanol for the synthesis of 2,6-dimethylnaphthalene

The methylation of 2-methylnaphthalene (2-MN) and methanol is a highly promising approach to synthesize 2,6-dimethylnaphthalene (2,6-DMN). However, it is difficult to control the target product selectivity. Herein, a series of HBEA/MTW composite molecular sieves by secondary crystallization were produced by hydrothermal method and further applied for the alkylation of 2-MN. The results showed that composite molecular sieves had higher specific surface area and porosity than mechanically mixed molecular sieves, and the secondary crystallization reduced acid amount and acid density. The composite molecular sieve performed better in the alkylation of 2-MN with methanol, improving reaction conversion and selectivity of 2,6-DMN. To further improve the catalytic performance, we used Mg to modify the pure molecular sieve. The selectivity of 2,6-DMN over 1%Mg-BEA/MTW catalyst can be further increased with the 2,6-/2,7-DMN ratio of 1.5. Therefore, the composite molecular sieves have a high potential for application in the methylnaphthalene alkylation reaction.

One-pot cogeneration of phenol-rich bio-oil, hydrogen-rich gas and solid carbon degradation material from reed

A newly developed two-step catalytic pyrolysis process (TSCP) based on poly-generation technology is proposed to convert reed straw (RS) into phenol-rich bio-oil, hydrogen-rich gas, and solid carbon degradation material over iron-loaded activated carbon. The effects of the first step pyrolysis temperature (T1) and catalyst composition on the product distribution and target product selectivity were investigated. When T1 was 350 °C and 10% Fe/AC catalyst was selected, the concentration of phenolic compounds and H2 peaked at 63.87 area% and 63.29 vol%, respectively. The iron-loaded activated carbon catalysts promoted the decarboxylation and decarbonylation reactions of cellulose and hemicellulose decomposition products, as well as the demethylation and demethoxylation reactions of lignin for the selective production of phenolic compounds and hydrogen gas. In addition, 94.7% quinclorac (10 mg/L) removal was achieved with 0.2 g/L 10% Fe/AC catalyst-doped pyrolysis carbon and 2 mM PMS within 90 min. This study could realize the high-value comprehensive utilization of reed and provide a reference for the full quantitative utilization of other agricultural and forestry wastes.

Mechanism of stability and deactivation of N-doped CuFeZn catalysts for C2+ alcohols synthesis by hydrogenation of CO2

The catalysts for synthesis of C2+ alcohols by hydrogenation of CO2 developed so far still have challenges in meeting expectations in terms of the target product selectivity and catalyst stability. In this work, nitrogen-doped CuFeZn catalysts by calcinated in nitrogen atmosphere show good catalytic activity and stability. The optimal PDA/CFZ-N450 exhibits outstanding C2+ alcohols selectivity of 39.75%. In addition, the stabilization period lasts for 264 h. The superior stability is closely related to the doped N. It is confirmed that the oxygen vacancies facilitate the activity of catalysts as well as stabilize the doped N species, which is correspondingly essential for the stability of the catalysts. However, sintering of active metals and migration of active species to the catalyst surface possibly leads to activity decline.

Promotional effect of Cs modification to NASICON material on aldol condensation of acetic acid and formaldehyde to acrylic acid

The production of high value-added oxygenated chemicals from methanol and its derivatives is one of the important ways of coal conversion and clean and efficient utilization. Herein, a series of environmentally-friendly Cs-modified NASICON materials were applied to catalyze the aldol condensation of acetic acid (HAc) and formaldehyde (FA) to acrylic acid (AA) and methyl acrylate (MA). Encouragingly, the selectivity of target products (AA + MA) was highly up to 92.2%, corresponding to the space–time-yield more than 48.0 μmol·gcat-1·min-1 over the 2Cs/NSC catalyst, achieving the synchronization of good selectivity and productivity for the target products. Characterization results demonstrated that the acid-base modulation by Cs was responsible for catalyst supremacy. The weak basic sites on catalyst surface were efficient in adsorbing and activating HAc. Plenty of acidic sites especially the medium-strong and strong acidic sites were more favorable for the AA formation.

Ir-CoO Active Centers Supported on Porous Al2 O3 Nanosheets as Efficient and Durable Photo-Thermal Catalysts for CO2 Conversion.

Photo-thermal catalytic CO2 hydrogenation is currently extensively studied as one of the most promising approaches for the conversion of CO2 into value-added chemicals under mild conditions; however, achieving desirable conversion efficiency and target product selectivity remains challenging. Herein, the fabrication of Ir-CoO/Al2 O3 catalysts derived from Ir/CoAl LDH composites is reported for photo-thermal CO2 methanation, which consist of Ir-CoO ensembles as active centers that are evenly anchored on amorphous Al2 O3 nanosheets. A CH4 production rate of 128.9 mmol gcat⁻ 1 h⁻1 is achieved at 250 °C under ambient pressure and visible light irradiation, outperforming most reported metal-based catalysts. Mechanism studies based on density functional theory (DFT) calculations and numerical simulations reveal that the CoO nanoparticles function as photocatalysts to donate electrons for Ir nanoparticles and meanwhile act as "nanoheaters" to effectively elevate the local temperature around Ir active sites, thus promoting the adsorption, activation, and conversion of reactant molecules. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) demonstrates that illumination also efficiently boosts the conversion of formate intermediates. The mechanism of dual functions of photothermal semiconductors as photocatalysts for electron donation and as nano-heaters for local temperature enhancement provides new insight in the exploration for efficient photo-thermal catalysts.

Research Progress of Co-Catalysts in Photocatalytic CO2 Reduction: A Review of Developments, Opportunities, and Directions

With the development of the global economy, large amounts of fossil fuels are being burned, causing a severe energy crisis and climate change. Photocatalytic CO2 reduction is a clean and environmentally friendly method to convert CO2 into hydrocarbon fuel, providing a feasible solution to the global energy crisis and climate problems. Photocatalytic CO2 reduction has three key steps: solar energy absorption, electron transfer, and CO2 catalytic reduction. The previous literature has obtained many significant results around the first two steps, while in the third step, there are few results due to the need to add a co-catalyst. In general, the co-catalysts have three essential roles: (1) promoting the separation of photoexcited electron–hole pairs, (2) inhibiting side reactions, and (3) improving the selectivity of target products. This paper summarizes different types of photocatalysts for photocatalytic CO2 reduction, the reaction mechanisms are illustrated, and the application prospects are prospected.

Constructing Defective Heterojunctions of BiOBr Nanosheets and Hollow NH2 -functionalized MOFs for Visible-light-driven CO2 Reduction with Nearly 100% CO Selectivity by Pure H2 O.

To rationally design photocatalysts with high generation rate and selectivity of target product remains an ongoing challenge for CO2 conversion in pure H2 O. Herein, from the viewpoint of enhancing the separation efficiency of photoinduced electron-hole pairs and the adsorption ability of CO2 molecule, we have constructed a series of Z-scheme defective heterojunctions of BiOBr nanosheets and hollow NH2 -functionalized metal-organic framework (MOF) MIL-125 with Ti ions as metal centers (noted as NH2 -MIL-125(Ti)). Systematic characterization demonstrates that the BiOBr nanosheets are anchored on the surface of hollow NH2 -MIL-125(Ti), which facilitates the efficient visible-light-driven catalytic reduction of CO2 to CO with nearly 100% selectivity by pure H2 O. Especially, the CO generation rate of optimized catalyst with oxygen vacancies reaches 459.7 μmol g-1 h-1 , which is higher than those of all the previously reported photocatalysts without sacrificial reagents. This approach provides a new insight for using inorganic semiconductors to fabricate semiconducting MOFs for high-efficiency photocatalytic reduction CO2 into value-added chemicals by pure H2 O.

0D/2D Z-schemed carbon nitride quantum dots/Bi2MoO6-x with enhanced carriers’ separation efficiency toward oxidation coupling of amines under ambient conditions

Organic synthesis driven by solar energy is receiving extensive attention due to its inherent merits like higher target product selectivity as well as milder reaction condition. While sluggish photoinduced charge carriers’ separation kinetic severely limited its utilization efficiency, leading to inefficient catalytic performance or energy-consuming reaction conditions. Assembling 0D/2D Z-schemed semiconductor nano-heterojunction would be a promising candidate for solving such problem. Herein, 0D/2D carbon nitride quantum dots (CNQDs)/Bi2MoO6-x (BMO-OD) was devised and synthesized by facile NaBH4-mediated hydrothermal method. The CNQDs/BMO-OD exhibited superior catalytic activity toward amines oxidation coupling under ambient conditions. Broad substrates suitability as well as excellent photochemical stability implies it would be a robust alternative amines oxidation coupling photocatalyst under mild conditions. The superior photocatalytic performance is attributed to expeditious photoinduced charge carriers’ separation and transfer of Z-schemed heterostructures and unique multipoint contact interface of 0D/2D. Scavenger experiments and ESR results demonstrates h+ and •O2– radicals play a major role in aerobic conditions while only h+ paly predominant role in anerobic conditions. The design and synthesis of 0D/2D CNQDs/BMO-OD Z-scheme heterostructures would be beneficial for boosting photoinduced carriers’ separation kinetic, thus promoting the photocatalytic oxidation coupling of amines under mild conditions.

High-yield production of liquid fuels in CO2 hydrogenation on a zeolite-free Fe-based catalyst.

Catalytic conversion of CO2 to long-chain hydrocarbons with high activity and selectivity is appealing but hugely challenging. For conventional bifunctional catalysts with zeolite, poor coordination among catalytic activity, CO selectivity and target product selectivity often limit the long-chain hydrocarbon yield. Herein, we constructed a singly cobalt-modified iron-based catalyst achieving 57.8% C5+ selectivity at a CO2 conversion of 50.2%. The C5+ yield reaches 26.7%, which is a record-breaking value. Co promotes the reduction and strengthens the interaction between raw CO2 molecules and iron species. In addition to the carbide mechanism path, the existence of Co3Fe7 sites can also provide sufficient O-containing intermediate species (CO*, HCOO*, CO3 2*, and ) for subsequent chain propagation reaction via the oxygenate mechanism path. Reinforced cascade reactions between the reverse water gas shift (RWGS) reaction and chain propagation are achieved. The improved catalytic performance indicates that the KZFe-5.0Co catalyst could be an ideal candidate for industrial CO2 hydrogenation catalysts in the future.