High Hydrogen Selectivity Research Articles

Bucket effect of Cobalt Nanoparticles and Single Atoms in Nitroarenes Transfer Hydrogenation

Synergetic metal nanoparticles (NPs) and single atoms hold significant potential in reactions that require activating multiple substrate molecules. However, due to the differences in adsorption, activation and kinetics among distinct substrates during the multistep reaction process, the synergy and matching relationship between metal NPs and single atoms remain unclear. In this work, we synthesized a series of Co1-NP/CNT@CN-X dual-site catalysts with tunable molar ratios (X%) of Co single atoms to total Co species through a coordination site regulation (CSR) strategy and investigated the bucket effect of the dual active sites in the transfer hydrogenation of nitro compounds. Density functional theory calculations reveal that active hydrogen generation from ammonia borane hydrolysis primarily occurs at the surface of Co NPs, while nitroarenes hydrogenation predominantly takes place at Co single atoms, which is consistent with experimental findings. The optimized Co1-NP/CNT@CN-7.6 maintains high selectivity for nitro hydrogenation (> 99.9%) and exhibits conversion (99.9%) nearly 3.7 times that of the original Co1-NP/CNT@CN-1.6 catalyst (27%), achieved by overcoming the bucket effect between Co NPs and single atoms. This work not only elucidates the synergistic mechanisms of dual sites in transfer hydrogenation, but also establishes that optimizing matching effect is an effective approach to significantly enhance their catalytic performance.

Highly Dispersed Pd@ZIF‐8 for Photo‐Assisted Cross‐Couplings and CO2 to Methanol: Activity and Selectivity Insights

AbstractOur study unveils a pioneering methodology that effectively distributes Pd species within a zeolitic imidazolate framework‐8 (ZIF‐8). We demonstrate that Pd can be encapsulated within ZIF‐8 as atomically dispersed Pd species that function as an excited‐state transition metal catalyst for promoting carbon–carbon (C−C) cross‐couplings at room temperature using visible light as the driving force. Furthermore, the same material can be reduced at 250 °C, forming Pd metal nanoparticles encapsulated in ZIF‐8. This catalyst shows high rates and selectivity for carbon dioxide hydrogenation to methanol under industrially relevant conditions (250 °C, 50 bar): 7.46 molmethanol molmetal−1 h−1 and >99 %. Our results demonstrate the correlations of the catalyst structure with the performances at experimental and theoretical levels.

Pt/MgO catalysts intrinsically promoted by fast moving bed pyrolysis for hydrogenation properties

Elucidating the correlation between the geometric/electronic structure of the catalyst and its catalytic performance is of paramount importance. However, achieving precise manipulation over the geometric/electronic structure of the catalyst remains a formidable challenge. Here, we develop a fast moving pyrolysis bed (FMPB) strategy to finely regulate the geometry structure (Pt metal particle size and Pt-O coordination number (CN)) and electronic structure of the Pt/MgO catalyst. It is found that the hydrogen dissociation energy barrier is negatively related to the Pt atom electron density. The Pt1/MgO-600-N2 (600 and N2 represented the temperature and atmosphere under fast pyrolysis, respectively) with highest electron density exhibits the highest para-chloronitrobenzene (p-CNB) hydrogenation activity (66978 h−1), which is ∼220 times that of Pt nanoparticles (NPs, Pt NPs/MgO), ∼58 times that of Pt1/MgO-400-air, and ∼3 times that of Pt nanoclusters (NCs, Pt NCs/MgO). DFT calculations disclose that Pt1/MgO-600-N2 with highest Pt-5d center, which is more conducive to hydrogen dissociation. The transition of the H2 cleavage mode from homolytic (Pt NPs/MgO) to heterolytic (Pt1/MgO-600-N2) makes it more favorable for the hydrogenation of the polar nitro functional group, ensuring that substantial enhancement in its activity while preserving high selectivity in hydrogenation.

Hydrogen Separation Membranes: A Material Perspective

The global energy market is shifting toward renewable, sustainable, and low-carbon hydrogen energy due to global environmental issues, such as rising carbon dioxide emissions, climate change, and global warming. Currently, a majority of hydrogen demands are achieved by steam methane reforming and other conventional processes, which, again, are very carbon-intensive methods, and the hydrogen produced by them needs to be purified prior to their application. Hence, researchers are continuously endeavoring to develop sustainable and efficient methods for hydrogen generation and purification. Membrane-based gas-separation technologies were proven to be more efficient than conventional technologies. This review explores the transition from conventional separation techniques, such as pressure swing adsorption and cryogenic distillation, to advanced membrane-based technologies with high selectivity and efficiency for hydrogen purification. Major emphasis is placed on various membrane materials and their corresponding membrane performance. First, we discuss various metal membranes, including dense, alloyed, and amorphous metal membranes, which exhibit high hydrogen solubility and selectivity. Further, various inorganic membranes, such as zeolites, silica, and CMSMs, are also discussed. Major emphasis is placed on the development of polymeric materials and membranes for the selective separation of hydrogen from CH4, CO2, and N2. In addition, cutting-edge mixed-matrix membranes are also delineated, which involve the incorporation of inorganic fillers to improve performance. This review provides a comprehensive overview of advancements in gas-separation membranes and membrane materials in terms of hydrogen selectivity, permeability, and durability in practical applications. By analyzing various conventional and advanced technologies, this review provides a comprehensive material perspective on hydrogen separation membranes, thereby endorsing hydrogen energy for a sustainable future.

Electric field-driven assembly of (110) oriented metal–organic framework ZIF-8 monolayer with high hydrogen selectivity

Metal-organic framework (MOF) membranes have showed great potential in gas separation. To date, it is still a great challenge to precisely control the optimal orientation of MOF membranes with an enhanced gas separation performance. Herein, we prepared a compact and (110) oriented ZIF-8 membrane with a thickness of about 265 nm on graphite substrate within 1 h at room temperature via electric-field-driven strategy. Since the membrane is an intergrown one-crystal layer, grain boundary retardation of the flux is eliminated. Furthermore, due to the reduction of the transport pathways through the oriented structure, the (110) oriented ZIF-8 membrane exhibits a high gas separation performance. At 100 °C and 1 bar for the separation of equimolar binary gas mixtures H2/CO2, H2/CH4 and H2/C3H8, separation factors of 49.5, 90.9 and 121.8 can be obtained, with H2 permeance of about 1.7 × 10-7 mol·m−2·s−1·Pa−1. The developed strategy exhibits excellent reproducibility and scalability, and a large area ZIF-8 membrane can be consistently prepared on the graphite substrate, thus facilitating the preparation and application of the ZIF-8 membrane on a large scale. Further, the electric-field-driven strategy is also helpful for the preparation oriented ZIF-67 and ZIF-L membranes, confirming its versatility for the preparation of oriented MOF membranes.

Highly Dispersed Pd@ZIF-8 for Photo-Assisted Cross-Couplings and CO2 to Methanol: Activity and Selectivity Insights.

Our study unveils a pioneering methodology that effectively distributes Pd species within a zeolitic imidazolate framework-8 (ZIF-8). We demonstrate that Pd can be encapsulated within ZIF-8 as atomically dispersed Pd species that function as an excited-state transition metal catalyst for promoting carbon-carbon (C-C) cross-couplings at room temperature using visible light as the driving force. Furthermore, the same material can be reduced at 250 °C, forming Pd metal nanoparticles encapsulated in ZIF-8. This catalyst shows high rates and selectivity for carbon dioxide hydrogenation to methanol under industrially relevant conditions (250 °C, 50 bar): 7.46 molmethanol molmetal-1 h-1 and >99%. Our results demonstrate the correlations of the catalyst structure with the performances at experimental and theoretical levels.

Cluster-Level Heterostructure of PMo12/Cu for Efficient and Selective Electrocatalytic Hydrogenation of High-Concentration 5-Hydroxymethylfurfural.

Electrochemical hydrogenation of aldehyde molecules, exemplified by 5-hydroxymethylfurfural (HMF), offers a sustainable approach for synthesizing higher value-added alcohols. However, severe coupling side reactions impede its practical implementation at high concentrations. In this work, a cluster-level heterostructure of a PMo12/Cu catalyst is synthesized by loading Keggin-type phosphomolybdic acid (H3PMo12O40, PMo12) onto Cu nanowires. The catalyst exhibits high selectivity in electrocatalytic hydrogenation (ECH) of HMF to 2,5-bishydroxymethylfuran (BHMF) under an unprecedentedly high substrate concentration of 1.0 M. Under -0.3 V (vs RHE) with 1.0 M HMF, PMo12/Cu shows a Faradaic efficiency as high as 98% with an excellent productivity of 4.35 mmol cm-2 h-1 toward BHMF, much higher than those on the pristine Cu nanowires. Mechanism studies and density functional theory calculations demonstrate that the heterostructural interface of PMo12/Cu serves as an active reaction center for the ECH. The unique electronic properties and geometric structure promote the dissociative reduction of water molecules to generate H* and reduce HMF with a decreased reaction energy barrier, which is responsible for exceptional reactivity and selectivity.

Investigation on the hydrogen production by methanol aqueous phase reforming over Pt/CexMg1-xO2 catalyst: Synergistic effect of support basicity and oxygen vacancies

Green hydrogen production from biomass oxygenated derivatives (methanol, ethanol, ethylene glycol, etc.) by low temperature aqueous phase reforming (APR) has the advantages of high hydrogen selectivity and low energy consumption. A series of CexMg1-xO2 mixed oxide supported catalysts were synthesized by a simple citric acid combustion method. The results show that these catalysts exhibit excellent water-gas shift reaction activity and CO is rarely detected in the products, which is due to their abundant oxygen vacancies of the mixed oxide supports of the Pt/CexMg1-xO2 catalysts. At the same time, the introduction of MgO provides more strong basic sites on the surface of mixed oxide support, and the methanol conversion and hydrogen yield show a volcano peak with the increasing number of basic sites and the hydrogen production reaches the highest (127.16 mmol) over Pt/Ce0·5Mg0·5O2 catalyst. The mixed oxide supported Pt/Ce0·5Mg0·5O2 catalyst enjoys the benefits of both oxygen vacancies in accelerating H2O adsorption/dissociation and strong basic sites in contributing to the formation of formate group (HCOO*), which improve the oxidation of CO* and APR activity. This synergistic effect is conducive to improve hydrogen yield of methanol APR and reduce CO selectivity to a minimum level.

Unveiling the formic acid dehydrogenation dynamics steered by Strength-Controllable internal electric field from barium titanate

Formic acid is a desirable liquid hydrogen storage compound for solving transport and storage problems of hydrogen for onboard fuel cells. Optimizing adsorption/desorption energy of intermediates can directly modulate the performance of Pd catalysts in formic acid dehydrogenation (FAD). Herein, we introduce internal electric field with controllable strength to regulate the adsorption/desorption of intermediates on Pd. Non-ferroelectric cubic-phase barium titanate (CBT) is heat-treated at high temperature to obtain ferroelectric tetragonal-phase barium titanate (TBT(C)), which exhibits internal electric field. The strength of the internal electric field is successfully adjusted by heat treatment at different temperatures. The size of Pd nanoparticles is restricted between 2.2 and 2.7 nm, and the electronic effect of Pd is effectively eliminated by coating TBT(C) with mesoporous carbon shell (TBT(C)@SC). Experimental results prove that the internal electric field promotes the desorption of hydrogen on Pd. Pd/TBT(C)@SC-800 obtained by heat treatment at 800 °C, with the optimal internal electric field strength, exhibits high activity and hydrogen selectivity for FAD. This work provides a new strategy for designing FAD catalysts.

Pd nanoflakes epitaxially grown on defect MoS2 nanosheets for enhanced nitroarenes hydrogenation to anilines

Hydrogenation of nitroarenes to anilines under mild conditions is attractive from both theoretical and practical viewpoints. Here, high-performance catalyst with layered Pd nanoparticles epitaxially growing on ultrathin MoS2 nanosheets (Pd/MoS2) were prepared. It shows surprisingly high catalytic activity, selectivity and stability for hydrogenation of various nitroarenes to corresponding anilines; the turnover frequency is one or two magnitudes higher than conventional Pd-based catalysts. Surface sulfur vacancies are formed on MoS2 nanosheets with low formation energy barrier. These S vacancies provide efficient positions for adsorbing Pd atoms, which enables facile cleavage of N–O bond as result of strong interfacial electron interaction that decreases activation energy by 0.41 eV in comparison with conventional Pd catalysts. In situ spectroscopy and DFT calculation results reveal a dual-site mechanism, in which surface Pd sites adsorb and dissociate H2 into active H*, and then readily reacts with nearby activated nitroarene to form aniline on interfacial Pd-MoS2 sites.

Preparation of Fe-based catalysts from waste biomass as a carbon carrier and its catalytic performance in CO2 hydrogenation

Fe/LC composite catalyst was synthesized by one-step carbonization method and exhibited high olefin selectivity in CO2 hydrogenation.

Mesoporous CeO2-supported ultrafine PdCu nanoparticle catalyst for selective hydrogenation of alkynols

Bimetallic PdCu nanoparticles were anchored on mesoporous CeO2, the obtained PdCu@CeO2 catalyst showed high selectivity for alkynols hydrogenation to produce high value-added enols.

Thermally induced intermetallic Rh1Zn1 nanoparticles with high phase-purity for highly selective hydrogenation of acetylene.

Ordered M1Zn1 intermetallic phases with structurally isolated atom sites offer unique electronic and geometric structures for catalytic applications, but lack reliable industrial synthesis methods that avoid forming a disordered alloy with ill-defined composition. We developed a facile strategy for preparing well-defined M1Zn1 intermetallic nanoparticle (i-NP) catalysts from physical mixtures of monometallic M/SiO2 (M = Rh, Pd, Pt) and ZnO. The Rh1Zn1 i-NPs with structurally isolated Rh atom sites had a high intrinsic selectivity to ethylene (91%) with extremely low C4 and oligomer formation, outperforming the reported intermetallic and alloy catalysts in acetylene semihydrogenation. Further studies revealed that the M1Zn1 phases were formed in situ in a reducing atmosphere at 400 °C by a Zn atom emitting-trapping-ordering (Zn-ETO) mechanism, which ensures the high phase-purity of i-NPs. This study provides a scalable and practical solution for further exploration of Zn-based intermetallic phases and a new strategy for designing Zn-containing catalysts.

First-principles study of CO2 hydrogenation on Cd-doped ZrO2: Insights into the heterolytic dissociation of H2.

Cd-doped ZrO2 catalyst has been found to have high selectivity and activity for CO2 hydrogenation to methanol. In this work, density functional theory calculations were carried out to investigate the microscopic mechanism of the reaction. The results show that Cd doping effectively promotes the generation of oxygen vacancies, which significantly activate the CO2 with stable adsorption configurations. Compared with CO2, gaseous H2 adsorption is more difficult, and it is mainly dissociated and adsorbed on the surface as [HCd-HO]* or [HZr-HO]* compact ion pairs, with [HCd-HO]* having the lower energy barrier. The reaction pathways of CO2 to methanol has been investigated, revealing the formate path as the dominated pathway via HCOO* to H2COO* and to H3CO*. The hydrogen anions, HCd* and HZr*, significantly reduce the energy barriers of the reaction.

Effect of Ca and Co over Ni–Al Mixed Oxides for Hydrogen Production by Ethanol Steam Reforming

Ni–Al layered double hydroxide‐derived catalyst is modified with Ca and Co to improve their properties for ethanol steam reforming (ESR). The catalysts are prepared by coprecipitation and are characterized through N2 adsorption–desorption measurements, X‐Ray diffraction, temperature programmed reduction, temperature programmed oxidation, and NH3‐temperature programmed desorption. Catalyst activity tests are performed between 400 and 600 °C with the calcined catalysts and without reduction using ethanol and water in a 1:3 ratio in a fixed bed reactor with online gas chromatography analysis. The partial substitution of Ni by Co and Ca decreases the acidity of the catalyst. All samples remain stable after the reaction at 600 °C for 8 h and present a full ethanol conversion and high hydrogen selectivity, above 90%. The samples modified by Ca or Co are reduced to metallic phase during the reaction and reveal a smaller crystallite size than NiAl. The sample with Ca prepared with a different precipitant results in a catalyst with a more thermally stable active phase, low acidity, and higher specific surface area. This catalyst presents smaller crystallite size and low‐carbon formation after the reaction at 600 °C for 8 h, demonstrating higher potential for hydrogen production by ESR.

Mechanism of the Hydrazine Monohydrate Decomposition by Means of IR Spectroscopy <i>In Situ</i>

Pd-containing catalysts (1%Pd/Al2O3 and 5%Pd/Al2O3) deposited on aluminum oxide were studied in the decomposition reaction of hydrazine monohydrate. According to in situ IR spectroscopy, it was found that hydrazine monohydrate is adsorbed on the coordination unsaturated centers of the catalyst surface in a linear form. When the temperature rises, the adsorbed hydrazine monohydrate loses a water molecule, which is accompanied by a change in the geometry of the molecular complex. Adsorption of hydrazine on a support and its diffusion onto palladium clusters is a more advantageous process than direct adsorption on active centers. This circumstance shows that the hydrazine adsorbed on the support can be an intermediate of its decomposition process. The studied catalysts have a maximum activity in the temperature range of 100–120°C, while the ratio of hydrogen and nitrogen concentrations in the reaction products was equal to 2, which corresponds to 100% selectivity for hydrogen. As the reaction temperature increases, the selectivity decreases significantly. The explanation of the high selectivity for hydrogen at low temperatures is due to the fact that the adsorption of N2H4 is carried out through the formation of hydrogen–metal bonds. The hydrogen–metal bond strength in such a complex is higher than the nitrogen–metal bond strength, hence the barrier for breaking the N–H bond is lower than the barrier for breaking N–N bond, which leads to breaking N–H bond and preserving the N–N bond. At elevated temperatures, some of the hydrogen atoms formed recombine, the other reacts with the surface complexes of hydrazine to form the intermediate NH3–NH3, the breaking of the bond in which leads to the formation of ammonia molecules in the gas phase.

Ni-Mn-N derived composite nitrogen carriers for enhanced chemical looping ammonia production

Chemical looping ammonia production (CLAP) technology provides additional freedom for the optimization of operating conditions via the strategy of stepwise reactions, which is promising to achieve green ammonia synthesis under mild conditions. Mn-based nitrogen carriers are ideal redox materials by virtue of their moderate thermodynamic properties and abundant crystalline phases, but their performance of hydrogenation in CLAP is still limited by the low reactivity. Herein, a series of Ni-Mn-N composite nitrogen carriers with different Ni/Mn ratios were prepared, and the effect of Ni doping on the performance of NH3 production was investigated at atmospheric pressure. The nitrogen carriers modified with low level of Ni (<20 wt%) showed high activity and selectivity of hydrogenation, and the effective conversion of lattice nitrogen in 80Mn20Ni-N reached 36.1% at 750 °C, which was 15.7% higher than the undoped 100Mn-N. The introduction of low level of Ni can simultaneously enhance the bulk migration and interfacial reaction of lattice nitrogen and achieve the optimal kinetic matching between the both processes, thus promoting the activity and selectivity of lattice nitrogen converted to NH3. This study presents new insights into the design of composite nitrogen carriers to enhance ammonia production in CLAP.

Effect of Different In2O3(111) Surface Terminations on CO2 Adsorption.

In2O3-based catalysts have shown high activity and selectivity for CO2 hydrogenation to methanol; however, the origin of the high performance of In2O3 is still unclear. To elucidate the initial steps of CO2 hydrogenation over In2O3, we have combined X-ray photoelectron spectroscopy and density functional theory calculations to study the adsorption of CO2 on the In2O3(111) crystalline surface with different terminations, namely, the stoichiometric, reduced, and hydroxylated surface. The combined approach confirms that the reduction of the surface results in the formation of In adatoms and that water dissociates on the surface at room temperature. A comparison of the experimental spectra and the computed core-level shifts (using methanol and formic acid as benchmark molecules) suggests that CO2 adsorbs as a carbonate on all three surface terminations. We find that the adsorption of CO2 is hindered by hydroxyl groups on the hydroxylated surface.

CuCoMgAlOx Mixed Oxides as Selective Catalysts for the Hydrogenation of Furan Compounds

Single phase CuCoMgAl-layered hydroxides were obtained by making fine adjustment to their composition through changing the (Co + Cu)/Mg = 0.5; 1; 2; 3 and Co/Cu = 0.5; 1; 2 ratios. The rise of Co/Cu in systems contributed to the increase in their thermal stability. CuCoMgAl-catalysts showed high selectivity of carbonyl group hydrogenation in furfural and 5-hydroxymethylfurfural. In furfural hydrogenation, the selectivity to furfuryl alcohol was more than 99%, and in 5-hydroxymethylfurfural hydrogenation, the selectivity to 2,5-hydroxymethyl furfural was 95%. The surface of the samples with different Co/Cu after calcination and reduction was the same and had a «core-shell» structure (TEM). «Core» consisted of Cu and Co metallic particles. «Shell» consisted of CuCoMgAlOx mixed no-stoichiometric spinel oxides. There was no sintering or change in size of the metallic particles after the reaction. For the sample with Co/Cu = 1, their phase composition after reaction remained unchangeable. The increase of Co/Cu led to the formation of an X-ray amorphous phase after the reaction. This suggests the decrease in structural stability of this sample. The obtained results prove the prospects of using bimetallic CoCu-systems for hydrogenation of furan aldehydes, and opens up new directions for further research and improvement.

Carbonate Hydrogenated to Formate in the Aqueous Phase over Nickel/TiO2 Catalysts.

Carbonate hydrogenation to formate is a promising route to convert captured carbon dioxide into valuable chemicals, thus reducing carbon emissions and creating a revenue return. Developing inexpensive catalysts with high activity, selectivity, and stability remains challenging. We report a supported non-noble metal catalyst, Ni/TiO2 , with great selectivity over 96 % and excellent stability in catalyzing the conversion of carbonate into formate in aqueous solution. Ni0 and Ni2+ species are both observed in Ni/TiO2 catalysts, and the synergistic effect of these two Ni components leads to high activity and high selectivity of carbonate hydrogenation to formate.