Atmospheric Pressure Of H2 Research Articles

Highly active palladium nanocatalyst for selective hydrogenation of 1,5-cyclooctadiene under atmospheric H2 pressure

An ionic liquid [CH3(OCH2CH2)22N+Et3][p-CH3C6H4SO3−] was synthesized and employed for stabilizing Pd nanocatalyst, which possesses the thermoregulated phase-separable property. The as-prepared Pd nanocatalyst was applied for the selective hydrogenation of 1,5-cyclooctadiene under atmospheric H2 pressure. The >99% conversion of 1,5-cyclooctadiene with 95% selectivity towards cyclooctene was achieved under the optimal reaction conditions. The Pd nanocatalyst could be reused for six cycles without evident loss in conversion and selectivity. The turnover frequency of 4232 h−1 is greater than those of previously reported Pd nanocatalyst under atmospheric H2 pressure.

Modulation of Pt states on Pt/ZnO for atmospheric ultra-deep desulfurization of dibenzothiophene and sustainable utilization

The relationship between active metals and desulfurization activity, ultra-deep desulfurization at atmospheric pressure, and the sustainable utilization of ZnO-based adsorbents are positive significance for designing high-efficiency adsorbents in the field of reactive adsorption desulfurization (RADS) to achieve atmospheric zero sulfur and promote sustainable development of adsorbents. However, no efficient approach has been developed to systematically and simultaneously study all three aspects. In this work, we explored Pt/ZnO with different Pt states by metal-support interaction and oxygen vacancy modulation for atmospheric RADS of dibenzothiophene (DBT). The relationship between metal-active Pt states and the desulfurization activity of DBT was well established. The limiting step of atmospheric DBT desulfurization over Pt/ZnO was proposed, providing a new understanding and supplementing of the current RADS reaction. Moreover, the feasibility of Pt/ZnO to achieve ultra-deep desulfurization of DBT under atmospheric H2 pressure was analyzed from kinetics (51.8 kJ/mol) and thermodynamics (kRADS = 4.4*10^7). The spent Pt/ZnO adsorbent with a saturated sulfur capacity could be sustainable utilized as a highly efficient (408 μmolDBT/gPt*min) and sulfur-tolerant (155 h) catalyst for DBT hydrodesulfurization. The work aims to suggest designs for efficient and sustainable adsorbents based on Pt/ZnO for ultra-deep desulfurization at atmospheric pressure, establishing the scientific basis for industrial applications of this process.

Pt nanoparticles confined in hollow silica nanoreactors as highly efficient catalysts for semihydrogenations of alkynes at atmospheric H2 pressure.

In this work, Pt nanoparticles encapsulated hollow porous silica nanoreactors (Pt@HPSNs) was synthesized in one-pot by a reverse microemulsion system, and they exhibit good catalytic efficiency and stability for semihydrogenations of alkynes. The key design concept is to form Pt hydroxide nanoparticles mixed poly(ethyleneimine) nano-aggregates in water droplets, which further functions as seeds for silica deposition and the void templates to form the central voids. The Pt@HPSNs illustrate a wide adaptability for semihydrogenations of a series of terminal alkynes to the corresponding alkenes at mild reaction conditions, and demonstrate high yields of styrene for semihydrogenation of phenylacetylene, showing good catalytic efficiency for hydrogenation of phenylacetylene to styrene at atmospheric H2 pressure. The enhanced catalytic performance of Pt@HPSNs are ascribed to their hollow porous nanostructures, where the confinement of Pt nanoparticles in voids increase the structural stability and the confinement effect may increase the collision of reactants and Pt, resulting in improved catalytic efficiency.

Hydrogenation of BHMF with controllable selectivity to tetrahydropyranone and 1-hydroxy-2,5-hexanedione under atmospheric H2pressure

BHMF was selectively transformed into different chemicals under atmospheric H2pressure by the selection of metal catalysts. A reasonable reaction mechanism was proposed through the combination of experimental and theoretical calculations.

E-selective Semi-hydrogenation of Alkynes under Mild Conditions by a Diruthenium Hydride Complex.

The synthesis, characterization and catalytic activity of a new class of diruthenium hydrido carbonyl complexes bound to the tBu PNNP expanded pincer ligand is described. Reacting tBu PNNP with two equiv of RuHCl(PPh3 )3 (CO) at 140 °C produces an insoluble air-stable complex, which was structurally characterized as [Ru2 (tBu PNNP)H(μ-H)Cl(μ-Cl)(CO)2 ] (1) using solid-state NMR, IR and X-ray absorption spectroscopies and follow-up reactivity. A reaction with KOtBu results in deprotonation of a methylene linker to produce [Ru2 (tBu PNNP* )H(μ-H)(μ-OtBu)(CO)2 ] (3) featuring a partially dearomatized naphthyridine core. This enables metal-ligand cooperative activation of H2 analogous to the mononuclear analogue, [Ru(tBu PNP*)H(CO)]. In contrast to the mononuclear system, the bimetallic analogue 3 catalyzes the E-selective semi-hydrogenation of alkynes at ambient temperature and atmospheric H2 pressure with good functional group tolerance. Monitoring the semi-hydrogenation of diphenylacetylene by 1 H NMR spectroscopy shows the intermediacy of Z-stilbene, which is subsequently isomerized to the E-isomer. Initial findings into the mode of action of this system are provided, including the spectroscopic characterization of a polyhydride intermediate and the isolation of a deactivated species with a partially hydrogenated naphthyridine backbone.

The application of nonthermal plasma in methanol synthesis via CO2 hydrogenation

AbstractCH3OH is an energy carrier that can be generated from renewable resources and be used as a fuel in fuel cells and internal combustion engines and a platform chemical for the synthesis of value‐added chemicals or gasoline. Carbon dioxide (CO2) hydrogenation is one of the widely researched methods to generate methanol. The traditional CO2 hydrogenation reaction method (requires high H2 pressure and temperatures) has attracted considerable attention. However, the new emerging field of catalysis referred to as nonthermal plasma (NTP) catalysis has also been developed extensively for methane reforming and CO2 hydrogenation to methane and CO. The plasma‐assisted approach not only presents remarkable advantages, such as room temperature and atmospheric H2 pressure but also has great potential to be powered by renewable electricity in a flexible way since it can be easily switched on/off. In this account, we review the recent articles published on methanol synthesis from CO2 and H2 using NTP. We reviewed and discussed the mechanism of this reaction under NTP, the modification of the reactor configurations, and the rationale behind the catalyst design. In the end, we discussed the advantages and disadvantages of each of these works and the future perspectives of this interesting privileged reaction. We believe this review is of interest to researchers active in sustainable heterogeneous catalysis.

Reduction of imines with a reusable bimetallic PdCo-Fe3O4 catalyst at room temperature under atmospheric pressure of H2.

Bimetallic nanocatalysts have been used for the development of organic reactions, owing to the synergistic effect between the transition metals. A new procedure for synthesizing amines by the reduction of imines with H2 at atmospheric pressure and room temperature in the presence of PdCo–Fe3O4 nanoparticles is reported. The straightforward procedure, mild reaction conditions, high turnover number, and recyclability extend the scope of this reaction to practical applications.

Hydrodeoxygenation of Aromatic Ketones under Mild Conditions over Pd-loaded Hydrogen Molybdenum Bronze with Plasmonic Features

Abstract Reduction of α-MoO3via “hydrogen spillover” process mediated by noble metal nanoparticles leads to a formation of hydrogen molybdenum bronze with plasmon-induced optical features. We herein report that Pd-loaded hydrogen molybdenum bronze effectively promotes the hydrodeoxygenation of aromatic ketones to the corresponding alkyl aromatics at room temperature and under atmospheric pressure of H2. The catalyst shows a further enhanced catalytic activity under the irradiation of visible light due to the plasmonic effect.

Hydrogenation of Toluene to Methyl Cyclohexane over PtRh Bimetallic Nanoparticle-Encaged Hollow Mesoporous Silica Catalytic Nanoreactors.

PtRh bimetallic nanoparticle (NP)-encaged hollow mesoporous silica nanoreactors (PtRh@HMSNs) are prepared by employing metal-ion-containing charge-driven polymer micelles as templates. These nanoreactors feature ∼1–2 nm PtRh NPs in ∼11 nm hollow cavities of HMSNs. Among various PtxRhy@HMSNs, Pt0.77Rh1@HMSNs show the best catalytic performance for toluene hydrogenation. Under 30 °C, atmospheric H2 pressure, and a toluene/(Pt+Rh) molar ratio of 200/1, Pt0.77Rh1@HMSNs reach 100.0% of methyl cyclohexane yield and demonstrate a much better catalytic performance than monometallic Pt@HMSNs and Rh@HMSNs and their physical mixtures. Moreover, Pt0.77Rh1@HMSNs exhibit a good catalytic stability during recycling experiments. The enhanced performance of Pt0.77Rh1@HMSNs is ascribed to the interaction between Pt and Rh, the beneficial effect of the relatively large mesoporous channels for mass transfer, as well as the confinement effect of functional NPs inside hollow cavities.

LOW-TEMPERATURE CARBONIZATION OF ACTIVE CENTERS IS THE REASON OF Pd/C CATALYSTS DEACTIVATION

Physicochemical and catalytic properties of Pd/C catalysts before and after the deactivation as a result of a dimethylbenzylamine debenzylation–acylation reaction are compared. A comprehensive analysis conducted by a number of methods (chemisorption, X-ray photoelectron spectroscopy, electron microscopy, X-ray diffraction) showed that a tenfold loss of the catalyst activity in the reaction conducted in soft conditions (atmospheric H2 pressure, 25 °C) is related to the formation of a nanoscale graphite phase. While this phenomenon is common for high temperature reactions, it is first discovered at low temperatures.

Catalytic Reductive Alkylation of Amines in Batch and Microflow Conditions Using a Silicon-Wafer-Based Palladium Nanocatalyst.

We describe the development of the catalytic reductive alkylation of amines with aldehydes under the atmospheric pressure of H2 using a brush-like silicon-nanostructure-supported palladium nanoparticle composite (SiNS–Pd) as a silicon-wafer-based reusable heterogeneous catalyst. The present reaction of primary and secondary amines with various aliphatic and aromatic aldehydes in the presence of the catalyst (0.02–0.05 mol % Pd) gave the corresponding secondary and tertiary amines including Lomerizine and Aticaprant in a 68% quantitative yield without overalkylation. We also designed and fabricated a flow device equipped with SiNS–Pd for microflow reactions, which was applied to the gas–liquid–solid triphasic reaction system (i.e., H2 gas, a substrate solution, and a solid catalyst). A multigram-scale reaction of aniline and benzaldehyde was demonstrated to obtain N-benzylaniline (ca. 4 g/day), in which the internal volume of the flow channel was 43 μL, the residence time was approximately 1 s, and the turnover number (TON) reached 4.0 × 104 in a continuous 24 h run (1.7 × 103 h–1; 0.50 s–1).

Deoxygenation of heptanoic acid to hexene over cobalt-based catalysts: A model study for α-olefin production from renewable fatty acid

Deoxygenation of heptanoic acid, a model compound, over bimetallic cobalt (Co-Pt, Co-Au, Co-Pd, Co-Ru) supported silica catalysts, was examined for α-olefin production. The catalysts were prepared by conventional impregnation of the metal precursors on silica and characterized by XRF, TEM, H2-TPR, acetic acid-TPD, and XANES. Catalytic testing was performed in a fixed-bed flow reactor under atmospheric H2 pressure. Monometallic cobalt catalysts yielded mainly 1-hexene, but rapid deactivation was observed. Incorporation of 0.5%wt secondary metal, particularly Pt, increases activity and stability under H2. A relatively higher olefin/paraffin ratio can be obtained from the reaction over 5%Co+0.5%Pt/SiO2 when compared to that with higher Pt loading. The co-impregnation method offers Co-Pt catalysts with stability higher than that prepared by the sequential impregnation method. Over cobalt-based catalysts, the deoxygenation is proposed to proceed via reduction of heptanoic acid to heptanal that is an intermediate for decarbonylation to hexene; while other side reactions are suppressed.

Gas-phase hydrodeoxygenation of phenol over Zn/SiO2 catalysts: Effects of zinc load, temperature, weight hourly space velocity, and H2 volumetric flow rate

The hydrodeoxygenation (HDO) of phenol catalyzed by Zn/SiO2 under atmospheric H2 pressure was investigated in a continuous fixed bed reactor. The effects of several process parameters (zinc load, reaction temperature, weight hourly space velocity (WHSV), and H2 volumetric flow rate) were evaluated to optimize process conditions. Phenol was selected as a stable model component for lignin degradation products in fast pyrolysis bio-oil. Silica-supported zinc catalysts were prepared with different loadings of the active metal (0.5%, 1%, 2%, 3%, and 4%) and assessed using characterization techniques such as XRD, ICP-OES, BET, H2-TPR/TPD, and FESEM–EDX. Reaction products including benzene, cyclohexene, and cyclohexane were identified through GC/FID analysis. Experimental results revealed that process yield increased with reaction temperature, metal loading, and WHSV. The selectivity percentages of the products were slightly changed by varying process parameters. Moreover, H2 volumetric flow rate exerted a negligible effect on product yield and selectivity.

Gas-phase hydrodeoxygenation of guaiacol over Ni-based HUSY zeolite catalysts under atmospheric H2 pressure

Hydrodeoxygenation (HDO) is considered as one of the most promising routes to upgrade bio-oil for high value-added chemicals. In the study, the gas-phase HDO of guaiacol in atmosphere and 350 °C over Ni-based catalysts modified by Fe, Ga, Ce, La, or Sm on HUSY zeolite support was carried on. The effect of promotors, bimetallic/monometallic catalysts and Ni loading on HDO activity was investigated. The results showed that phenols and aromatic hydrocarbon were the main products and Ni was the main metal active site. Compared with monometallic metal catalysts, the promoters, such as Fe, Ga, Ce, La, and Sm, inhibited the aggregation of Ni, promoted Ni dispersion, and improved the HDO activity of guaiacol significantly. The highest conversion of 98.36% was performed over 10%Sm-20%Ni/HUSY, and the highest degree of hydrodeoxygenation (HDO%) of 7.7% was obtained over 10%La–20%Ni/HUSY catalysts. For Ce, Ga, and Fe modified catalysts, hydroquinone selectivity was higher than that over La and Sm modified catalysts. However, for La and Sm modified catalysts, phenols selectivity increased, and more aromatic hydrocarbon was formed. The HDO activity was improved via increasing Ni loading. Direct deoxygenation and hydrogenation were the more reasonable reaction pathways for gas phase guaiacol atmospheric HDO over Ni-based bimetallic HUSY catalysts.

Reduction of Propanoic Acid over Pd‐Promoted Supported WOx Catalysts

AbstractSilica‐, titania‐, and zirconia‐supported tungsten oxide catalysts were synthesized by wetness impregnation techniques. When promoted with Pd, these materials catalyzed the reduction of propanoic acid to 1‐propanol at 433 K with a selectivity of up to 92 % (13.5 % conversion) in atmospheric pressure of H2. Over Pd‐promoted WOx/TiO2, the observed orders of reaction were 0.2 in H2 and 0.7 in propanoic acid, and the apparent activation energy was 54 kJ mol−1. In situ X‐ray absorption spectroscopy of Pd‐promoted WOx/SiO2 revealed a slight reduction of the W from +6 to an average oxidation state of about +5 during H2 treatment above 473 K. In situ infrared spectroscopy indicated the catalyst surface was covered mostly by propanoate species during reaction. For comparison, supported phosphotungstic acid was also evaluated as a catalyst under identical conditions, but the resulting high acidity of the catalyst was deleterious to alcohol selectivity.

The effect of H2 pressure on the reduction kinetics of hematite at low temperatures

Two novel experimental approaches to study the reduction kinetics of hematite (Fe2O3) by hydrogen at low temperatures are presented. Experiments were carried out in batch reactors at 200 °C and at H2 pressures of 3, 6 and 8 MPa, respectively. Complementary experiments were performed in an open system at atmospheric H2 pressure and 270 °C. Here the reaction product water in the effluent gas was quantified in short intervals by gas chromatography (Thermal Conductivity Detector; TCD). The mineralogical changes over time were assessed by X-ray powder diffraction with Rietveld analysis, scanning electron microscopy and the measurement of magnetic hysteresis loops.While the phase conversions of hematite → magnetite → Fe(0) are occurring consecutively in open systems (p(H2)≈0.1 MPa), in closed systems at elevated H2 pressure both reduction products are observed simultaneously. At 200 °C the reaction rates are about one order of magnitude lower than at 270 °C. The conversion rate of magnetite → Fe(0) is highly sensitive to the hydrogen pressure with a rate increase by a factor of 2.5 upon an increase of p(H2) from 3 to 6 MPa and by 2.0 between 6 and 8 MPa.

Selective Room‐Temperature Hydrogenation of Carbonyl Compounds under Atmospheric Pressure over Platinum Nanoparticles Supported on Ceria‐Zirconia Mixed Oxide

A Pt/CeO2‐ZrO2 catalytic system was able to initiate an extremely intense hydrogen spillover providing a huge amount of activated hydrogen (12 mol/mol Pt) at temperatures –50°C ‐ +25°C, which was not observed before. The idea was to use this activated hydrogen for reduction of carbonyl compounds under ambient conditions. Thus, the efficient and selective heterogeneous hydrogenation of carbonyl compounds of different structure, including 5‐hydroxymethylfurfural and cinnamaldehyde, to the corresponding alcohols with quantitative yields was successfully performed over the Pt/CeO2‐ZrO2 catalysts at room‐temperature and atmospheric pressure of H2. The proposed catalysts afforded hydrogenation under significantly milder conditions with a much higher activity and selectivity compared to the commercial catalysts and reported catalytic systems. Hydrogenation of the C=O bond in the presence of a C=C bond proceeded with a high regioselectivity.

Highly Efficient Pt-Catalyst Supported on Mesoporous Ceria-Zirconia Oxide for Hydrogenation of Nitroaromatic Compounds to Anilines

In this work, we have prepared a new catalytic system based on highly dispersed Pt nanoparticles supported on mesoporous ceria-zirconia oxide. The unique ability of the synthesized catalyst to activate hydrogen in the temperature range from –50 to 25°C allows us to provide selective hydrogenation of nitro-aromatic compounds to anilines at room temperature and atmospheric pressure of H2.

An alternative route of CO2 conversion: Pd/C-catalyzed oxazolidinone hydrogenation to HCOOH and secondary alkyl-(2-arylethyl)amines with one stone two bird strategy

The oxazolidinone as one kind of annular CO2 derivatives has been hydrogenated by a new catalytic system Pd/C-TMGPEG150Me (polyethylene glycol-functionalized 1,1,3,3-tetramethyl guanidine), affording two valuable products i.e. formic acid and the corresponding secondary alkyl-(2-arylethyl)amines in the high yields of 89% and 98%, respectively. This hydrogenation can be carried out smoothly under relatively mild conditions of 60 °C, 4 MPa of H2 with a liquid/solid carbon source (oxazolidinone) instead of high pressure CO2. The notable results can be successfully obtained even at room temperature under atmospheric H2 pressure. This one stone two bird strategy is applicable to series of 5-aryl-2-oxazolidinones and opens up a novel way of synthesizing linear secondary alkyl-(2-arylethyl)amines without the selectivity issues, and validates a potential alternative approach for indirect conversion of CO2 to energy-related products formic acid, as oxazolidinones can be readily obtained from hydrogenation of CO2.

New Insights into the Kinetics of Structural Transformation and Hydrogenation Activity of Nano-crystalline Molybdenum Carbide

Transformation of cubic molybdenum carbide into hexagonal β-Mo2C was found to follow the Avrami–Erofeev kinetic model with an n parameter of four indicating a slow nucleation step with a polyhedral growth of the transformed phase. The transformation not only occurred at 773 K under atmospheric H2 pressure, but also imperceptibly occurred under the employed hydrogenation reaction conditions (413 K and 70 psig of H2 pressure) when using toluene or 1-octene as reactants, not affecting the activity under the steady state. Our computational studies also revealed that both crystal structures share common atomic cluster arrangements with small differences in angles and interatomic distances. The transformation was triggered by local distortions which favored shorter and more homogeneous interatomic distances as present in the hexagonal phase. The prepared molybdenum carbide materials were selective to the hydrogenation of 1-octene under the mild hydrogenation conditions tested. Hydrogenation of 1-octene was preferential in a 50 wt% mixture of toluene and 1-octene with minimal toluene hydrogenation under the tested conditions.