Hydrogenation Activity Research Articles

Elevating dimethyl oxalate hydrogenation activity over core–shell Cu/SiO2@CeO2 catalysts

Increasing dimethyl oxalate (DMO) hydrogenation activity remains a challenge. A Cu catalyst was designed by creating Cu nanoparticles (NPs) over SiO2 layer formed on the CeO2 particles (SiO2@CeO2) using the ammonia evaporation method followed by the calcination and reduction step. The optimized 30Cu/SiO2@5CeO2 catalyst shows good performance in the micro-packed bed reactor (100 % DMO conversion, 95.9 % ethylene glycol (EG) selectivity, 200 h stability) under the condition of the ratio of H2 to DMO (H2/DMO) = 30, 190 °C and 2 MPa in the run, and CeO2 was proved to be effective in the DMO hydrogenation process. The exposed CeO2 on the surface of catalyst was found to facilitate the formation of Cu+ by its interaction between adjacent Cu nanoparticles, resulting in the faster adsorption and dissociation of C=O bond on the catalyst surface, according to the characterization results obtained by the XRD, XPS and in situ FT-IR, etc.

The synergistic effect of Cl doping and Bi coupling to promote the carrier separation of BiOBr for efficient photocatalytic nitrogen reduction

Photocatalytic nitrogen reduction reaction (NRR) is a sustainable process for ammonia synthesis under mild conditions. However, photocatalytic NRR activity and are generally limited by inefficient carrier separation and transfer. Therefore, parallel engineering of bulk phase doping and surface coupling is critical to achieving the goal of efficient NRR. In this study, Cl doped BiOBr nanosheet assemblies (BiOBr/Cl) were constructed in delicately designed deep eutectic solvents (DESs), combined with ionothermal methods at low temperatures and Bi3+ exsolution reduction strategy at high temperatures. The unique liquid state and reducibility of DESs induce the reduction of Bi3+ and the in situ coupling of Bi quantum dots at the surface of BiOBr/Cl nanosheets along with the construction of Bi-BiOBr/Cl nanosheet assemblies. The experimental results show that Cl doping could reduce the exciton dissociation energy and promote its dissociation to free carriers. Bi quantum dots could form tightly coupled Schottky junction with BiOBr/Cl enabling the efficient and unidirectional transmission of photogenerated electrons from BiOBr/Cl to metal Bi. The formed electron deficient region at Schottky interface promotes the adsorption and activation of N2. The hierarchical structure of Bi-BiOBr/Cl nanosheet assembly benefits to providing more N2 adsorption active sites. The DFT calculation shows that the accumulation of high concentration of active hydrogen in Bi-BiOBr/Cl leads to a significant decrease of energy barrier of the first step hydrogenation of N2. Bi-BiOBr/Clis more inclined to adsorb nitrogen for NRR in comparison with H* for hydrogen production. The synergistic effect of Cl doping and Bi coupling result in a high NRR activity of Bi-BiOBr/Cl photocatalyst of 6.67 mmol·g−1·h−1, which was 11.3 times higher than that of initial BiOBr. This study provides a promising strategy for designing highly active NRR photocatalysts with high efficiency carrier dissociation and transport.

Re‐Examination of Self‐Decay Chemistry of Phthalimide‐N‐oxyl Redox‐Organocatalyst for Free‐Radical CH‐Functionalization – Puzzle Begins to Come Together

AbstractPhthalimide‐N‐oxyl radicals (PINO) are catalytically active hydrogen abstracting species generated from N‐hydroxyphthalimide (NHPI) – one of the most efficient and widely used organocatalysts for free‐radical oxidative CH‐functionalization processes. The self‐decay of PINO is one of the main limiting factors of NHPI usage, but currently there is no consensus on the mechanism of this important process. In the present work, quantitative EPR and NMR monitoring of PINO generation and degradation along with decay product analysis and control experiments allowed us to build a consistent picture of PINO decay chemistry and put together previously contradictory results. PINO yields achievable employing various oxidants were measured and compared for the first time. At least two PINO decay pathways were revealed: “trimerization” (with partial fragmentation, favored by high PINO concentrations at initial stage of decay), and medium oxidation favored by low PINO concentrations. The main PINO decomposition product, the “trimer” can easily be recycled back to NHPI.

Construction of Frustrated Lewis Pairs in Poly(heptazine Imide) Nanosheets via Hydrogen Bonds for Boosting CO2 Photoreduction

AbstractThe creation of frustrated Lewis pairs on catalyst surface is an effective strategy for tuning CO2 activation. The critical step in the formation of frustrated Lewis pairs is the spatial effect of proximal Lewis acid‐Lewis base pairs. Here, we demonstrate a facile surface functionalization methodology that enables hydrogen bonding between N and H atoms to mediate the construction of frustrated Lewis pairs in poly(heptazine imide), thereby increasing the propensity to activate CO2 molecules. Experimental and theoretical results show that the construction of active hydrogen bonding regions can facilitate the bending of CO2 molecules. Furthermore, the delocalization of electron clouds induced by the hydrogen bonding‐mediated frustrated Lewis pairs can promote the heterolytic cleavage and photocatalytic conversion of CO2. This work highlights the potential of utilizing hydrogen bonding‐mediated strategy in heterogeneously photocatalytic activation of CO2 over polymer materials.

Construction of Frustrated Lewis Pairs in Poly(heptazine Imide) Nanosheets via Hydrogen Bonds for Boosting CO2 Photoreduction.

The creation of frustrated Lewis pairs on catalyst surface is an effective strategy for tuning CO2 activation. The critical step in the formation of frustrated Lewis pairs is the spatial effect of proximal Lewis acid-Lewis base pairs. Here, we demonstrate a facile surface functionalization methodology that enables hydrogen bonding between N and H atoms to mediate the construction of frustrated Lewis pairs in poly(heptazine imide), thereby increasing the propensity to activate CO2 molecules. Experimental and theoretical results show that the construction of active hydrogen bonding regions can facilitate the bending of CO2 molecules. Furthermore, the delocalization of electron clouds induced by the hydrogen bonding-mediated frustrated Lewis pairs can promote the heterolytic cleavage and photocatalytic conversion of CO2. This work highlights the potential of utilizing hydrogen bonding-mediated strategy in heterogeneously photocatalytic activation of CO2 over polymer materials.

Dual-enzyme inhibiting nanomedicines for enhanced cancer chemodynamic therapy by inducing intratumoral acidosis

Deficiency of endogenous hydrogen peroxide and insufficient intracellular acidity are usually two important factors limiting chemodynamic therapy (CDT). Here we report a glutathione-responsive nanomedicine that can provide a suitable environment for CDT by inhibiting dual-enzymes simultaneously. The nanomedicine is constructed by encapsulation of a novel hydrogen sulfide donor in nanomicelle assembled by glutathione-responsive amphiphilic polymer. In response to intracellular glutathione, the nanomedicine can efficiently release the active ingredients hydrogen sulfide, carbonic anhydrase inhibitor and ferrocene. The hydrogen sulfide can increase the concentrations of hydrogen peroxide and lactic acid by inhibiting catalase and enhancing glycolysis. The carbonic anhydrase inhibitor can further induce intratumoral acidosis by inhibiting the function of carbonic anhydrase IX. Therefore, the nanomedicine can provide more efficient reaction conditions for the ferrocene-mediated Fenton reaction to generate abundant toxic hydroxyl radicals. In vivo results show that the combination of enhanced CDT and acidosis can effectively inhibit tumor growth. This design of nanomedicine provides a promising dual-enzyme inhibiting strategy to enhance antitumor efficacy of CDT.

Pd0–Ov–Ce3+ Interfacial Sites with Charge Redistribution for Enhanced Hydrogenation of Methyl Oleate to Methyl Stearate

Improving the efficiency of metal/reducible metal oxide interfacial sites for hydrogenation reactions of unsaturated groups (e.g., C=C and C=O) is a promising yet challenging endeavor. In our study, we developed a Pd/CeO2 catalyst by enhancing the oxygen vacancy (OV) concentration in CeO2 through high-temperature treatment. This process led to the formation of an interface structure ideal for supporting the hydrogenation of methyl oleate to methyl stearate. Specifically, metal Pd0 atoms bonded to the OV in defective CeO2 formed Pd0–OV–Ce3+ interfacial sites, enabling strong electron transfer from CeO2 to Pd. The interfacial sites exhibit a synergistic adsorption effect on the reaction substrate. Pd0 sites promote the adsorption and activation of C=C bonds, while OV preferably adsorbs C=O bonds, mitigating competition with C=C bonds for Pd0 adsorption sites. This synergy ensures rapid C=C bond activation and accelerates the attack of active H* species on the semi-hydrogenated intermediate. As a result, our Pd/CeO2-500 catalyst, enriched with Pd0–OV–Ce3+ interfacial sites, demonstrated excellent hydrogenation activity at just 30 °C. The catalyst achieved a Cis–C18:1 conversion rate of 99.8% and a methyl stearate formation rate of 5.7 mol/(h·gmetal). This work revealed the interfacial sites for enhanced hydrogenation reactions and provided ideas for designing highly active hydrogenation catalysts.

Visible core spectroscopy at Wendelstein 7-X.

This paper presents an overview of recent hardware extensions and data analysis developments to the Wendelstein 7-X visible core spectroscopy systems. These include upgrades to prepare the in-vessel components for long-pulse operation, nine additional spectrometers, a new line of sight array for passive spectroscopy, and a coherence imaging charge exchange spectroscopy diagnostic. Progress in data analysis includes ion temperatures and densities from multiple impurity species, a statistical comparison with x-ray crystal spectrometer measurements, neutral density measurements from thermal passive Balmer-alpha emission, and a Bayesian analysis of active hydrogen emission, which is able to infer electron density and main ion temperature profiles.

Rh, Co, and N-doped titanium mesh-based carbon nanosheet arrays for enhanced nitrite reduction reaction and ammonia generation

The electrocatalytic transformation of nitrite pollutants into valuable ammonia is crucial for the nitrogen cycle. However, the complex multi-reaction process necessitates the development of highly efficient and selective electrocatalysts. This study focuses on the creation of Rh-doped Co@NC anchored on a titanium mesh as an electrocatalyst to enhance the electrocatalytic nitrite reduction reaction (eNO2RR) for NH3 synthesis. By doping a trace amount of Rh within zeolitic imidazolate framework-67 nanosheets and subsequently pyrolyzing the material, uniformly distributed Rh and Co nanoparticles are anchored onto N-functionalized porous carbon nanosheet arrays. Consequently, the three-dimensional electrode enhances mass and electron transfer while providing abundant surface-exposed active sites for NH3 generation through eNO2RR. The Rh0.6 wt%–Co@NC/TM electrocatalyst, with a minimal Rh loading of 0.6 wt%, exhibits the highest Faradaic efficiency of 98.8 ± 0.7 % at −0.3 V, along with an NH3 yield of 1777.1 ± 7.0 μmol h−1 cm−2 at −0.7 V. Additionally, the electrocatalyst demonstrates exceptional durability over 20 consecutive cycles and remarkable environmental adaptability. Extensive experimental studies reveal that the superior performance of Rh0.6 wt%–Co@NC/TM arises from the synergistic catalysis between Co and Rh, which enhances NO2– adsorption and the production of active hydrogen for eNO2RR to NH3 synthesis. This research highlights that Rh incorporation facilitates the kinetics of eNO2RR and offers valuable insights for the development of efficient electrocatalysts towards NH3 synthesis.

Regulating Second-Shell Coordination in Cobalt Single-Atom Catalysts toward Highly Selective Hydrogenation.

Manipulating the local coordination environment of central metal atoms in single-atom catalysts (SACs) is a powerful strategy to exploit efficient SACs with optimal electronic structures for various applications. Herein, Co-SACs featured by Co single atoms with coordinating S atoms in the second shell dispersed in a nitrogen-doped carbon matrix have been developed toward the selective hydrogenation of halo-nitrobenzene. The location of the S atom in the model Co-SAC is verified through synchrotron-based X-ray absorption spectroscopy and theoretical calculations. The resultant Co-SACs containing second-coordination shell S atoms demonstrate excellent activity and outstanding durability for selective hydrogenation, superior to most precious metal-based catalysts. In situ characterizations and theoretical results verify that high activity and selectivity are attributed to the advantageous formation of the Co-O bond between p-chloronitrobenzene and Co atom at Co1N4-S moieties and the lower free energy and energy barriers of the reaction. Our findings unveil the correlation between the performance and second-shell coordination atom of SACs.

Boosting the Hydrogen Evolution Performance of Ultrafine Ruthenium Electrocatalysts by a Hierarchical Phosphide Array Promoter

Tuning the chemical and structural environment of Ru-based nanomaterials is a major challenge for achieving active and stable hydrogen evolution reaction (HER) electrocatalysis. Here, we anchored ultrafine Ru nanoparticles (with a size of ~4.2 nm) on a hierarchical Ni2P array (Ru/Ni2P) to enable highly efficient HER. The Ni2P promoter weakened the adsorption of proton on Ru sites by accepting electrons from Ru nanoparticles. Moreover, the hierarchical Ni2P endowed Ru catalysts with a large surface area and stable open structure. Consequently, the as-fabricated Ru/Ni2P electrode displayed a low overpotential of 57 and 164 mV at the HER current densities of 10 and 50 mA cm−2, respectively, comparable to the state-of-the-art Pt catalysts. Moreover, the Ru/Ni2P electrode can operate stably for 96 h at 50 mA cm−2 without performance degradation. After pairing with a commercial RuO2 anode, the Ru/Ni2P anode catalyzed overall water splitting at 1.73 V with a current density of 10 mA cm−2, which was 0.16 V lower than its commercial Ni counterpart. In situ Raman studies further revealed the optimized proton adsorption at the Ru-active sites on Ni2P promoter, thus enhancing the electrocatalytic HER performance.

Influence of support polarity on the selective hydrogenation of nitrostyrene over Pt-based heterogenous catalysts

Enhancing the selectivity of noble metal containing heterogeneous catalysts in the nitro group hydrogenation of functionalized nitroarenes is challenging due to high dependence of selectivity on the catalyst structure. Most reports focus on the influence of metal nanoparticles (NPs) size, confinement, and support-metal interactions, while the effect of support polarity remains unclear. Herein we investigate, for the first time, the influence of support polarity on the selective hydrogenation of NO2 in 3-nitrostyrene over Pt-based heterogeneous catalysts and compare it to the effects of Pt NPs size and location. To achieve this, we confined Pt NPs in the channels of the nonpolar Silicalite-1 (S-1) and benchmarked against catalysts with NPs of various sizes supported on polar SiO2 and nonpolar S-1.We demonstrate that support polarity is the key factor determining selectivity, surpassing the roles of Pt particle size and confinement. Catalysts with the nonpolar Silicalite-1 support exhibit higher NO2 selectivity compared to SiO2-based ones, with a threefold increase observed for Pt@S–S-1 compared to a commercial Pt/SiO2. DRIFT spectroscopy-monitored adsorption experiments and hydrogenation experiments of nitrobenzene and styrene model molecules show that the S-1 support favors the adsorption of –NO2 and the –NH2 formed during the reaction, impeding C=C hydrogenation. To a lower extent, the size of Pt NPs contributed to the obtained results with decreased C=C hydrogenation observed over smaller Pt NPs. Finally, confining Pt in the zeolite restricts the NPs growth during catalyst activation, resulting in a further decrease of particles size and C=C hydrogenation activity.

Modulating the Surface Concentration and Lifetime of Active Hydrogen in Cu-Based Layered Double Hydroxides for Electrocatalytic Nitrate Reduction to Ammonia

Modulating the Surface Concentration and Lifetime of Active Hydrogen in Cu-Based Layered Double Hydroxides for Electrocatalytic Nitrate Reduction to Ammonia

Precise design and construction of NiO-Ni heterostructures for active hydrogen evolution photocatalysis

The design of metal-oxide-metal heterostructure photocatalysts is an effective and widely used approach to solve global environmental problems. In this work, we designed and prepared a NiO-rich NiO-Ni heterostructure in an N-doped carbon matrix as a photocatalyst using a simple chemical method for hydrogen evolution reactions. It has an optimal photocatalytic hydrogen production rate of 1395 μmol. g−1. h−1, which is ∼8 times higher than that of Ni rich NiO-Ni (178 μmol. g−1. h−1). Combined experimental results demonstrate that such a good performance benefits from the specific NiO-Ni interface, which could improve the utilization of sunlight and charge separation efficiency. Moreover, this interface contributes to improved structural stability during the photocatalytic reactions, ensuring superior catalytic performance. This work provides a new strategy for the design and synthesis of efficient precious-metal-free heterostructure catalysts for photocatalytic hydrogen evolution reactions.

Structural Ni0-Niδ+ Pair Sites for Highly Active Hydrogenation of Nitriles to Primary Amines.

Supported metal pair sites have sparked interest due to their tremendous potential as bifunctional catalysts. Here, we report the structural Ni0-Niδ+ pair sites constructed in a well-defined nanocrystal phase of Ni3P. These Ni0-Niδ+ pair sites exhibited a remarkable product formation rate of 123 molBA/molmetal/h for the hydrogenation of benzonitrile (BN) to benzylamine (BA). The heterogeneity of surface Ni atoms over the Ni3P crystal created two types of metal centers, Ni0 and Niδ+, with a specific spatial distance of 4-5 Å. The Ni0 site acted as the center for H2 activation, while the Niδ+ site served as the adsorption and activation center for the C ≡ N group. The highly efficient cooperation effect of Ni0-Niδ+ pair sites resulted in a TOF of 2915 h-1 in BN hydrogenation, which is 2.4 and 9.7 times higher than that over the mono-Ni0 and -Niδ+ sites, respectively.

Density functional theory and ReaxFF MD study on steam-induced nitrogen migration mechanism during char gasification

The formation of nitrogen-containing species during char gasification is crucial for emission of nitrogenous pollutants. In this work, the detailed nitrogen migration mechanism during char gasification is studied. Density functional theory (DFT) coupled with ReaxFF MD methods are used to conduct an in-depth analysis on the intrinsic reaction mechanism during Char(N) and steam interaction. DFT results show that orbital electrons of carbon atoms on char surface are driven towards nitrogen atoms by nitrogen functional groups. The electron density of adjacent carbon atoms is weakened, which has a positive charge. Orbital electron properties show that the band energy gaps of three Char(N) models are 3.063 eV, 1.092 eV and 3.328 eV, indicating the reactivity order for three Char(N) models is as follows: Char(N)-2＞Char(N)-1＞Char(N)-3. DFT calculation indicates that the interaction between Char(N) and steam reduces unsaturated carbon atoms and lower the char decomposition activity, which will inhibit the yield of HCN. In contrast, through hydrogen transfer reactions, nitrogen atoms are easily combined with hydrogen atoms, which is more conducive to the formation of ammonia. ReaxFF MD modeling proves that HCN is the main product for Char(N) decomposition under inert atmosphere. Under steam atmosphere, nitrogen atoms in char are more likely to be converted into amino products. The induction of steam provides a large number of active hydrogen radicals, which is able to attack the nitrogen atoms of char and form N–H bonds, thus promoting the formation of ammonia.

Anionic Surfactant-Modulated Electrode-Electrolyte Interface Promotes H2O2 Electrosynthesis.

Conventional strategies for highly selective and active hydrogen peroxide (H2O2) electrosynthesis primarily focus on catalyst design. Electrocatalytic reactions take place at the electrified electrode-electrolyte interface. Well-designed electrolytes, when combined with commercial catalysts, can be directly applied to high-efficiency H2O2 electrosynthesis. However, the role of electrolyte components is equally crucial but is significantly under-researched. In this study, anionic surfactant n-tetradecylphosphonic acid (TDPA) and its analogs are used as electrolyte additives to enhance the selectivity of the two-electron oxygen reduction reaction. Mechanistic studies reveal that TDPA assembled over the electrode-electrolyte interface modulates the electrical double-layer structure, which repels interfacial water and weakens the hydrogen-bond network for proton transfer. Additionally, the hydrophilic phosphonate moiety affects the coordination of water molecules in the solvation shell, thereby directly influencing the proton-coupled kinetics at the interface. The TDPA-containing catalytic system achieves a Faradaic efficiency of H2O2 production close to 100% at a current density of 200mA cm-2 using commercial carbon black catalysts. This research provides a simple strategy to enhance H2O2 electrosynthesis by adjusting the interfacial microenvironment through electrolyte design.

Exploring the key role of electronic effects in Pd catalysts supported on Ni-modified N-doped porous carbon for direct synthesis of H2O2 under atmospheric pressure

Developing high-performance catalysts for direct synthesis of hydrogen peroxide (H2O2; DSHP) remains challenging. The paper proposes a strategy to optimize Pd catalysts by enriching Ni-modified N-doped porous carbon. The theoretical studies indicate that Ni modulates the electronic structure of Pd through charge transfer and strain effects, effectively reducing the adsorption energy of reaction intermediates. Furthermore, the Crystal Orbital Hamilton Population (COHP) analysis demonstrated that the energy-integrated COHP (ICOHP) of the OO bonds in O2* (* denotes the adsorbed state), OOH*, and HOOH* were positively correlated with dissociation activation energies and negatively correlated with hydrogenation activation energies. The modulation of the electronic structure of Pd by Ni reduces the hydrogenation activation energies of O2* and OOH* and increases the dissociation activation energies of O2*, OOH*, and HOOH*, thereby enhancing the selectivity and productivity of H2O2. The experimental results aligned with the theoretical predictions, showcasing that the optimized Pd-Ni7.5/NPCs catalyst exhibited remarkable H2O2 selectivity and productivity of 70.5 % and 230.31 mol kgcat-1·h-1, respectively, surpassing the performance of Pd/NPCs (47.1 % and 52.3 mol kgcat-1·h-1). This study offers profound insights into the crucial role of electron effects in DSHP using nickel-modified palladium catalysts, providing strong evidence into the design and optimization of Pd catalysts.

Tuning the CO2 hydrogenation activity and selectivity of TiO2 nanorods supported Rh catalyst via secondary‐metals addition

AbstractSecondary‐metals promotion is key to tune the CO2 hydrogenation performance of Rh‐based catalyst. We describe the addition of Cu or Co in TiO2 nanorods supported Rh catalyst (viz., RhMx/TiO2), showing significant impact on the CO2 hydrogenation activity and productivity. Cu addition can promote the partial hydrogenation to alcohols (methanol and ethanol), whereas Co led to the deep hydrogenation to alkanes (CH4, C2H6). Comparative time‐resolved in situ DRIFTS studies with H2/D2 isotopic exchange further reveal that both surface adsorbed CO* and formates could be the key reaction intermediates during the CO2 hydrogenation over RhMx/TiO2 (especially the RhCu2.5/TiO2), in which the interaction strength of CO* regulated by secondary‐metals addition was key to tune the reaction pathways and productivity. The findings suggested that rational design of active metal sites, for example the synergy between Rh and secondary‐metals, is highly needed to promote the CO insertion and CC coupling to produce ethanol.

Electrochemical Hydrogen Peroxide Generation and Activation Using a Dual-Cathode Flow-Through Treatment System: Enhanced Selectivity for Contaminant Removal by Electrostatic Repulsion.

To oxidize trace concentrations of organic contaminants under conditions relevant to surface- and groundwater, air-diffusion cathodes were coupled to stainless-steel cathodes that convert atmospheric O2 into hydrogen peroxide (H2O2), which then was activated to produce hydroxyl radicals (·OH). By separating H2O2 generation from its activation and employing a flow-through electrode consisting of stainless-steel fibers, the two processes could be operated efficiently in a manner that overcame mass-transfer limitations for O2, H2O2, and trace organic contaminants. The flexibility resulting from separate control of the two processes made it possible to avoid both the accumulation of excess H2O2 and the energy losses that take place after H2O2 has been depleted. The decrease in treatment efficacy occurring in the presence of natural organic matter was substantially lower than that typically observed in homogeneous advanced oxidation processes. Experiments conducted with ionized and neutral compounds indicated that electrostatic repulsion prevented negatively charged ·OH scavengers from interfering with the oxidation of neutral contaminants. Energy consumption by the dual-cathode system was lower than values reported for other technologies intended for small-scale drinking water treatment systems. The coordinated operation of these two cathodes has the potential to provide a practical, inexpensive way for point-of-use drinking water treatment.