Deep Hydrogenation Research Articles

Hydrogenating Polyethylene Terephthalate into Degradable Polyesters

The recycling and upcycling of polyethylene terephthalate (PET), the most widely used polyester plastic globally, has attracted growing attention concerning its disposal as non‐degradable waste in the natural environment. Transforming end‐of‐life PET into (bio)degradable polyester offers a novel approach to managing its waste. In this study, we introduce a simple process capable of converting waste PET into degradable polyester, polyethylene terephthalate‐polyethylene‐1,4‐cyclohexanedicarboxylate (PET‐PECHD), by partly hydrogenating the aromatic rings (x) into aliphatic ones (y). The polyesters with variable x/y compositions ranging from 100/0 to 0/100 can be achieved, and the molecular weight (Mw) can be maintained when x/y > 87/13 due to the nonobvious depolymerization. Pronounced depolymerization would occur with deeper hydrogenation, which generates a blend of PET‐PECHD and polyethylene‐1,4‐cyclohexanedicarboxylate (PECHD) with lower Mw, and finally a single‐type polymer PECHD. The PET‐PECHD demonstrates comparable thermal stability and mechanical strength compared to PET, along with superior extensibility, barrier properties, and (bio)degradability in acidic, alkaline solutions, and moist soil. This research highlights the potential for cost‐effective, large‐scale production of degradable polyester from real‐life plastic waste.

Hydrogenating Polyethylene Terephthalate into Degradable Polyesters.

The recycling and upcycling of polyethylene terephthalate (PET), the most widely used polyester plastic globally, has attracted growing attention concerning its disposal as non-degradable waste in the natural environment. Transforming end-of-life PET into (bio)degradable polyester offers a novel approach to managing its waste. In this study, we introduce a simple process capable of converting waste PET into degradable polyester, polyethylene terephthalate-polyethylene-1,4-cyclohexanedicarboxylate (PET-PECHD), by partly hydrogenating the aromatic rings (x) into aliphatic ones (y). The polyesters with variable x/y compositions ranging from 100/0 to 0/100 can be achieved, and the molecular weight (Mw) can be maintained when x/y > 87/13 due to the nonobvious depolymerization. Pronounced depolymerization would occur with deeper hydrogenation, which generates a blend of PET-PECHD and polyethylene-1,4-cyclohexanedicarboxylate (PECHD) with lower Mw, and finally a single-type polymer PECHD. The PET-PECHD demonstrates comparable thermal stability and mechanical strength compared to PET, along with superior extensibility, barrier properties, and (bio)degradability in acidic, alkaline solutions, and moist soil. This research highlights the potential for cost-effective, large-scale production of degradable polyester from real-life plastic waste.

CO2-assisted Controllable Synthesis of PdNi Nanoalloys for Highly Selective Hydrogenation of Biomass-derived 5-Hydroxymethylfurfural.

The selective hydrogenation of 5-hydroxymethylfurfural (HMF) to 2,5-bishydroxymethyltetrahydrofuran (BHMTHF), a vital fuel precursor and solvent, is crucial for biomass refining. Herein, we report highly selective and stable PdNi nanoalloy catalysts for this deep hydrogenation process. A CO2-assisted green method was developed for the controllable synthesis of various bimetallic and monometallic catalysts. The PdNi/SBA-15 catalysts with various Pd/Ni ratios exhibited a volcano-like trend between BHMTHF yield and Pd/Ni ratio. Among all catalysts tested, Pd2Ni1/SBA-15 achieved the best performance, converting 99.0% of HMF to BHMTHF with 96.0% selectivity, surpassing previously reported catalysts. Additionally, the Pd2Ni1/SBA-15 catalyst maintained excellent stability even after five recycling runs. Catalyst characterizations (e.g., HAADF-STEM) and DFT calculations confirmed the successful formation of the alloy structure with electron transfer between Ni and Pd, which accounts for the remarkable performance and stability of the catalyst. This work paves the way for developing highly selective and stable alloy catalysts for biomass valorization.

NiMo-MMO catalyst derived from LDHs precursors toward the deep hydrogenation of pyrene

A series of Ni-based catalysts were prepared via structural topological transformation from the Ni@Al2O3 layered double hydroxides (LDHs) precursors, and applied for the deep catalytic hydrogenation saturation of pyrene in a high-pressure reactor. The pore structures, active species dispersion, surface morphology, amount and type of acid of the prepared catalysts were characterized by BET, XRD, SEM, TEM, XPS, SEM, NH3-TPD and Py-IR. We studied the influence of physicochemical properties of Ni-based catalysts on the regularity and mechanism of deep hydrogenation of pyrene. Meanwhile, the synergy between Ni and Mo, and the interaction between active metals and support were discussed to further reveal the constitutive relationship during the hydrogenation reaction of pyrene. The results of the evaluation of the catalytic hydrogenation of pyrene show that the as-prepared NiMo mixed metal oxide (MMO) catalyst showed excellent catalytic activity: ∼95% pyrene conversion, 90.12% for the selectivity of deep hydrogenation products (hexahydropyrene, decahydropyrene and hexadecahydropyrene). It was expected that the successfully preparation and utilization of NiMo-MMO catalyst could provide a theoretical basis for the design of this kind of catalysts for deep catalytic hydrogenation of polycyclic aromatic hydrocarbons (PAHs).

Natural Hydrogen, the Ultimate Green Energy: Current Status and Prospects

Natural hydrogen is green hydrogen that is naturally produced on Earth, that is, an energy source that does not emit carbon without using additional energy for production. Since carbon is emitted from the existing gray hydrogen and blue hydrogen, green hydrogen with perfect eco-friendliness has been required. Natural hydrogen is produced through four mechanisms: serpentinization, radioactive decomposition, magma gas removal, and rock destruction and can exist in the dissolved ․ content of fluid mammals. Representative sites discovered to date include Mali, Africa, Brazil, and Australia, and each topography has different characteristics. Although reserves are estimated using geochemical and geophysical exploration technologies, the reliability is not high because the deep hydrogen flow in various geological environments is not considered. Based on this, this study drew the following conclusions. 1) Hydrogen can realize carbon neutrality with high energy content and independence, but 2) economic feasibility cannot be evaluated due to the uncertainty of the reserves and current reserves of natural hydrogen. Therefore, 3) for commercial use, leakage detection technology is required along with an understanding of the mechanism for generating natural hydrogen.

Highly efficient lignin depolymerization and enhanced bio-oil upgrading via in-situ hydrogenation: Impact of lignin structure

The inherent structural rigidity of lignin poses a significant challenge to its direct hydrogenation to produce aromatic compounds, requiring harsh reaction conditions. In this study, microwave-assisted hydrothermal liquefication was employed to rapidly generate raw bio-oil under mild conditions, coupled with an in-situ hydrogenation strategy to upgrade its quality. A series of lignin substrates were characterized to establish the relationship between lignin characteristics and aromatic products. Grass lignin can produce low molecular weight bio-oil in high yields (50.4–60.7 %) within 30 min at 180 °C, which is attributed to the abundance of cleavable β-O-4 linkages in its uniform structure. In contrast, softwood lignin with abundant guaiacyl (G) units possessed a robust thermal stability, resulting in a low monomer yield, but a high selectivity to G-type products (97 %). The raw bio-oil was further upgraded through in-situ hydrogenation with Pd catalysts. Low reaction temperatures (60–100 °C) favored the hydrogenation of aromatic aldehydes and ketones to their alcohol products, while high temperatures (100–220 °C) promoted the deep hydrogenation of aromatic side chains to alkyl products. Besides, an upgraded bio-oil with a higher heating value (29.8 MJ/kg) was obtained. Furthermore, the hydrogenation mechanism was investigated through the kinetics of simulated bio-oils. The activation energy follows the order: dimer β-O-4 linkage < monomer aldehyde group < ketone group < CC linkage, which is consistent with the hydrogenation kinetics observed in real lignin bio-oil. Overall, this study highlights the impact of lignin characteristics on subsequent conversion and alsoenhances our understanding of the complex depolymerization/hydrogenation mechanisms during lignin upgrading.

Manipulation of Oxygen Species on an Antimony-Modified Copper Surface to Tune the Product Selectivity in CO2 Electroreduction.

Rational regulation of the electrochemical CO2 reduction reaction (CO2RR) pathway to produce desired products is particularly interesting, yet designing economical and robust catalysts is crucial. Here, we report an antimony-modified copper (CuSb) catalyst capable of selectively producing both CO and multicarbon (C2+) products in the CO2RR. At a current density of 0.3 A/cm2, the faradaic efficiency (FE) of CO was as high as 98.2% with a potential of -0.6 V vs reversible hydrogen electrode (RHE). When the current density increased to 1.1 A/cm2 at -1.1 V vs RHE, the primary products shifted to C2+ compounds with a FE of 75.6%. Experimental and theoretical studies indicate that tuning the potential could manipulate the oxygen species on the CuSb surface, which determined the product selectivity in the CO2RR. At a more positive potential, the existence of oxygen species facilitates the potential-limiting step involving *COOH formation and reduces the adsorption of *CO intermediates, thereby promoting CO production. At a more negative potential, the localized high CO concentration coupled with the enhanced adsorption of *CO intermediates due to Sb incorporation facilitates C-C coupling and deep hydrogenation processes, resulting in an increased C2+ selectivity.

Hydrogen spillover enhances the selective hydrogenation of α,β-unsaturated aldehydes on the Cu–O–Ce interface

The industrially important selective hydrogenation of α,β-unsaturated aldehydes to allyl alcohol is still challenging to realize using heterogenous hydrogenation catalysts. Supported Cu catalysts have shown moderate selectivity, yet low activity for the reaction, due to the electronic structure of Cu. By anchoring atomically dispersed Pd atoms onto the exposed Cu surface of Cu@CeO2, we report in this work that hydrogen spillover activates the inert metal-oxide interfaces of Cu@CeO2 into highly effective and selective catalytic sites for hydrogenation under mild reaction conditions. The as-prepared catalysts exhibit much higher catalytic activity in the selective hydrogenation of acrolein than Cu@CeO2. Comprehensive studies reveal that atomically dispersed Pd species are critical for the activation and homolytic splitting of H2. The activated H atoms easily spill to the Cu–O–Ce interfaces as Cu–Hδ– and interfacial Ce–O–Hδ+ species, making them the active sites for hydrogenation of polar C=O bonds. Moreover, the weak adsorption of allyl alcohol on the Pd and Cu–O–Ce interfacial sites prevents deep hydrogenation, leading to selective hydrogenation of several α,β-unsaturated aldehydes. Overall, we demonstrate here a synergic effect between single atom alloy and the support for activation of an inert metal-oxide interface into selective catalytic sites.

Boosting hydrocarbon conversion via Cu-doping induced oxygen vacancies on CeO2 in CO2 electroreduction

Conversion of CO2 back to hydrocarbons is the most direct way of closing the “carbon cycle”, and its significance is further enlarged if this process is driven by renewable energies such as electricity. However, precisely controlling the product selectivity towards hydrocarbons against the competitive hydrogen evolution remains challenging, especially for Cu-based catalysts. Herein, we report a novel defect engineering strategy, by which Cu-doping-induced oxygen vacancies on CeO2 nanorods were effectively created, with adjustable vacancy/Cu ratio. The resulting optimum catalyst shows up to 79% catalytic current density to hydrocarbons (excluding CO), with 49% faradaic efficiency to CH4. Experiments and density functional theory unveil that the ratio between oxygen vacancy and Cu affects significantly the formation of *CHO and activation of H2O, which leads to the following deep hydrogenation to hydrocarbons. These findings may spur new insights for designing and developing more controllable chemical process relevant to CO2 utilization.

The Support and Bimetallic Synergy Effects in Cu‐Ni/SiO2 Catalysts for Hydrogenation of Furfural

AbstractHerein, a series of Cu, Ni catalysts were synthesized using mesoporous SiO2 (MCM‐41) and fumed SiO2 as supports for the catalytic hydrogenation of furfural (FF). The MCM‐41 support facilitated the high dispersion of Cu, Ni nanoparticles (NPs), and the hydrogenation products are primarily in the form of alcohols. For fumed SiO2, the proper amounts of acid sites contributed to the better selectivity of 2‐methyltetrahydrofuran(2‐MTHF). Hydrogenation results showed that the 10Cu10Ni/MCM‐41 catalyst afforded a 93.6 % yield of tetrahydrofurfuryl alcohol (THFA), while the 10Cu10Ni/SiO2 catalyst afforded a 61.73 % yield of 2‐MTHF and a 31.63 % yield of THFA. Meanwhile, it is also found that impregnating nickel salt before copper salt is more likely to promote the formation of deep hydrogenation products. Cyclic experiments indicate that developing a one‐step hydrogenation process with selective production of fully hydrogenated products is still a daunting and challenging task.

Spontaneous spatial-optimizing CO2 electroreduction to C2H4 over dynamically synergistic Cu-Bi pair

In CO2 electroreduction, mutative intermediates and the challenging CC coupling necessitate the spatial interplay between active sites and through dynamically optimizing configurations. Herein, we anchor ethylenediaminetetraacetic acid (EDTA)-bonded Cux+/Bi3+ pair within UiO-66 for a spontaneous spatial-optimizing CO2-to-C2H4 electroreduction. Ab initio molecular dynamic (AIMD) simulation visualizes that such metal pair adaptively interacts with intermediates. Density functional theory (DFT) elicits the componential synergy, in which an upshift d-band of Cu activates CO2 being protonated into *COOH while Bi site stabilizes oxygenated dimers for deep hydrogenation. The dynamic feature of such pair affords large freedom for sorption and migration of various intermediates, which consequently bestows UiO-66-EDTA/CuBi a maximal FEC2H4 of 47 % and a total current density over 100 mA cm−2 in the flow cell.

Electronic interaction between sub-nanometric Ru entity and TiO2 support regulates the hydrogenation chemistry for selective C-O bond cleavage

Selective C-O bond cleavage without ring saturation is the pillar pursuit in the hydrotreating process for lignin valorization/depolymerization since it avoids the consumption of excessive hydrogen. In this work, the sub-nanometric cluster and nanometric particle of Ru were supported on TiO2 for the hydrogenolysis of C-O bond in aromatic ether. The experimental and theoretical results reveal that, in the catalyst of larger Ru nanoparticles, less electron transfer occurs from individual Ru atom to TiO2, making the Ru-related domains retain the nature of bulky Ru for deep hydrogenation. Sub-nanometric Ru cluster shows more intense electron transfer for individual Ru atom, leading to a stronger modification to Ru domain by TiO2. Such electronic hybridization makes Ru gain the catalytic property of TiO2 to attenuate the activation of aromatic ring, inhibiting ring saturation with maintained C-O cleavage activity. This work implies that further decrease of Ru entity size to single-atom level may achieve the complete inhibition of ring saturation.

Short-stage synthesis of metal–ceramics composites as precursors for high performance catalytic applications

NiAl, NiCoAl, and CoCuAl intermetallics on ceramic TiC and TiCrC supports were produced by self-propagating high-temperature synthesis (SHS) from granular mixtures and used as precursors for preparation of catalysts for CO and propane deep oxidation and CO2 hydrogenation. The precursors were converted into catalysts by aluminum leaching and stabilization with hydrogen peroxide solution. Prepared supported catalysts were characterized by XRD, SEM/EDS, and BET methods and tested in the processes of deep oxidation of CO and propane and methanation of CO2. It was revealed that 100 % CO conversion is observed in TiC-supported catalysts at 250 °C. Catalysts containing NiCo active phase on both ceramic supports were shown to be the most active in propane oxidation. In CO2 methanation, Ni/TiCrC sample showed the highest CO2 conversion (58.9 % at 350 °C) with 100 % methane selectivity.

Deep Hydrogen Reservoirs and Longevity

The oceans are voluminous H2O reservoirs that regulate climate and life on Earth. Yet much larger H2O reservoirs, potentially accounting for several oceans, may exist in the Earth’s mantle and core in the form of H atoms trapped into the structure of nominally anhydrous minerals (NAMs) and metallic alloys. Determining the size of these ‘hidden oceans’ is key to understanding planetary evolution and surface dynamics and can be done by combining data from rare natural samples with experimental and theoretical models. The longevity of these deep H reservoirs is controlled by H transport rates over geological times, which are dominated by percolation rates, once H partitions into melts, or by plate mobility, if H remains locked in NAMs.

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.

Molecular Engineering of Hydrogen-Bonded Organic Framework for Enhanced Nitrate Electroreduction to Ammonia.

Electrocatalytic nitrate reduction is an efficient way to produce ammonia sustainably. Herein, we rationally designed a copper metalloporphyrin-based hydrogen-bonded organic framework (HOF-Cu) through molecular engineering strategies for electrochemical nitrate reduction. As a result, the state-of-the-art HOF-Cu catalyst exhibits high NH3 Faradaic efficiency of 93.8%, and the NH3 production rate achieves a superior activity of 0.65 mmol h-1 cm-2. The in situ electrochemical spectroscopic combined with density functional theory calculations reveals that the dispersed Cu promotes the adsorption of NO3- and the mechanism is followed by deoxidation of NO3- to *NO and accompanied by deep hydrogenation. The generated *H participates in the deep hydrogenation of intermediate with fast kinetics as revealed by operando electrochemical impedance spectroscopy, and the competing hydrogen evolution reaction is suppressed. This research provides a promising approach to the conversion of nitrate to ammonia, maintaining the nitrogen balance in the atmosphere.

Deep learning-based hydrogen leakage localization prediction considering sensor layout optimization in hydrogen refueling stations

To address the challenge and reliance on subjective experience in monitoring hydrogen leaks at hydrogen refueling stations (HRS), a regression prediction model for leakage localization based on Temporal convolutional network (TCN) and multimodal fusion technology is proposed for the first time. This model can accurately predict the spatial coordinates where the leakage source occurs in HRS. This study constructed a baseline dataset of hydrogen leakage, assisted by CFD simulation. Genetic Algorithm (GA) optimized the sensor layout to lower application costs while increasing monitoring effectiveness. The wind speed, wind direction, and hydrogen concentration data collected are multimodally fused to help the model mine more potential features. We compared the proposed model with current classical algorithms such as LSTM, GRU. The results demonstrate that our model achieves higher accuracy, delivering a localization model with an average error of just 0.54 m. The proposed method can provide guidance for the layout of monitoring sensors in the large-scale HRS and provide more accurate diagnostic results for hydrogen leakage behaviors to ensure the safe operation of HRS compared to other methods.

Electron-rich Ni3Zn strongly interacted on ZnO promoter for deep hydrogenation of phenanthrene in dibenzothiophene

Simultaneous hydrogenation of polycyclic aromatic hydrocarbons and sulfur contaminates (dibenzothiophene, DBT) in coal tar remains a challenge for energy utilization and environmental remediation. Herein, Ni3Zn/ZnO–Al2O3 catalysts with different ZnO loading were prepared for deep hydrogenation of phenanthrene (PHE) and synchronous removal of DBT in a fixed-bed reactor. Compared to Ni/Al2O3, the optimal Ni3Zn/ZnO–Al2O3 exhibited superior catalytic performance of 100.0% PHE conversion and 92.5% perhydrophenanthrene selectivity with 100.0% DBT conversion at 300 °C under 6 MPa for 10 h in a fixed-bed reactor. The kinetic study for PHE hydrogenation and mechanism for DBT hydrodesulfurization on Ni catalysts were discussed. Electron transfer from Zn to Ni over the active sites weakened DBT adsorption rather than PHE adsorption. The strong interactions between Ni3Zn and ZnO–Al2O3 supports facilitated sulfur migration from the alloy to intimate ZnO, preventing the deactivation of Ni active centers by sulfur deposition and poisoning.

In situ investigation of hydrogen embrittlement induced by δ phase in selective laser-melted GH4169 superalloy

Direct evidence of hydrogen-assisted crack nucleation and propagation associated with the δ phase in the selective laser melted GH4169 superalloy was obtained. The analysis of hydrogen trapping sites using thermal desorption spectroscopy revealed that the δ phase exhibits strong hydrogen capture capability, with a hydrogen desorption activation energy of 35.45 ± 2.51 kJ/mol. In addition, spatially resolved hydrogen mapping conducted by scanning Kelvin probe force microscopy and hydrogen microprint technique provided further evidence for the δ phase as a deep hydrogen trapping site. The atomic-scale characterization sufficiently reveals the deformation mechanism of the δ phase induced by dislocation accumulation. Hydrogen-promoted dislocation slip localization facilitates the formation of microvoid defects in the δ phase, which is the main reason for the δ phase fracture, and induces intergranular and transgranular cracks.

Silica nanospheres-encapsulated polymer ligands-bound Pd nanoparticles as highly efficient and selective catalysts for semi-hydrogenations of alkynes

In this work, we report that poly (acrylic acid) (PAA) and poly (ethylenimine) (PEI) capped Pd nanoparticles (NPs) encaged in hollow silica nanospheres (PAA/PEI-Pd@HSNs) function as highly efficient and selective catalysts for hydrogenations of a series of alkynes. We used the coordination of Pd4+ ions with PEI and PAA to build the micelles system in an ethanol-water system, which was employed as the templates for silica deposition and following NaBH4 reduction to give PAA/PEI-Pd@HSNs. The materials feature polymer-coordinated small Pd NPs inside silica nanospheres with thin shells and large cavities. The PAA/PEI-Pd@HSNs exhibit extremely high catalytic efficiency and reusability with enhanced alkene selectivity of ∼90 % at near complete conversions for hydrogenation of a series of alkynes, and maintain high selectivity even with a significantly extended reaction time. The enhanced catalytic performance of PAA/PEI-Pd@HSNs is ascribed to their thin silica shells/large cavities to improve the catalytic activity, PEI/PAA ligands that inhibit the deep hydrogenation of alkenes to alkanes on Pd NPs, and the protection of silica shells for inner ligands and Pd NPs to improve the reusability.