Anaerobic Dehydrogenation Research Articles

Cooperative S-S coupling and H2 production from photocatalytic dehydrogenation of thiols over ReSe2/ZnIn2S4 heterostructure

Photocatalytic anaerobic dehydrogenation provides a new avenue to cooperatively produce clean fuels and fine chemicals, while minimizing waste discharge and reducing environmental impact. Here, we demonstrate an efficient co-production of disulfides and H2 via photocatalytic S-S dehydrogenation of thiols using a two-dimensional (2D) heterostructure of ultrathin ZnIn2S4 (ZIS) nanosheets decorated with dispersed (1T phase) ReSe2 nanoparticles. Experimental characterizations and DFT calculations reveal that integrating ReSe2 with ZIS leads to the formation of a robust internal electric field (IEF) within the ReSe2/ZIS heterostructure. The distorted 1T phase ReSe2 with abundant active Se sites and a high Fermi level induces downward band bending of ZIS at the interface, which promotes charge separation and expedites H2 evolution. Moreover, the introduction of ReSe2 provides more adsorptive sites, increasing the concentration of reactants on the catalyst surface. This enhancement fosters surface interactions between the catalyst and p-toluenethiol (PTT), ultimately accelerating the reaction rate. The optimal H2 and S-S coupling p-tolyl disulfide (PTD) production rates of the 5 wt% ReSe2/ZIS composite reach 2275 and 2303 µmol g−1h−1, respectively, approximately 5 times greater than those of blank ZIS. Importantly, the selectivity of PTD reaches 98.4 %. This visible-light-driven dehydrogenation process aligns with the principles and objectives of green chemistry, realizing high atom economy without generating byproducts. It is anticipated to open new possibilities for sustainable and environmentally friendly routes for synthesizing high-value chemicals and producing clean energy.

Advancements in biomass conversion: Copper-catalyzed anaerobic dehydrogenation of 5-hydroxymethylfurfural to 2,5-diformylfuran

Developing cost-effective and inherently safe methods for accelerating the sustainable production of value-added chemicals from biomass presents a promising solution to the current energy crisis. This study introduces heterogeneous copper species anchored on a γ-Al2O3 catalyst (Cu/γ-Al2O3) with high dispersibility and small Cu particle size, synthesized via a straightforward incipient-wetness impregnation method. This method facilitates the selective anaerobic dehydrogenation of 5-hydroxymethylfurfural (HMF) into 2,5-diformylfuran (DFF) in the absence of any oxidant or hydrogen acceptor. An HMF conversion of 69.8 % and a DFF yield of 44.9 % were attained at 130 °C over a 12-h period. Extensive characterizations were conducted to elucidate the correlation between the catalyst’s structure and its dehydrogenation activity. The findings indicated that strong L-acid sites, elevated Cu dispersions, small Cu particle size and an increased number of Cu+ active sites were conducive to enhanced dehydrogenation reactivity. The Cu/γ-Al2O3 catalyst demonstrated superior catalytic efficiency and stability. A possible reaction mechanism is suggested, integrating DFT calculations with experimental observations. This research offers valuable insights into the selective conversion of HMF to DFF and encourages further exploration into the dehydrogenation of biomass alcohols into high-value chemicals under oxidant-free conditions.

Directing the CdS nanosheet and nanowire to high efficiency for photocatalytic anaerobic dehydrogenation of benzyl alcohol to benzaldehyde by depositing Au25 nanoclusters

The photocatalysis of direct dehydrogenation of benzyl alcohol to benzaldehyde is an energy saving way to synthesize fine chemicals and pure hydrogen by using solar energy. The CdS-based catalysts were one of the typical kinds of photocatalysts for this reaction. The morphology of CdS could be easily tuned, which could greatly influence the photocatalytic performances. However, the morphology effect of CdS on the photocatalytic behaviour of the direct dehydrogenation of benzyl alcohol has not been investigated yet. In this work, we synthesized CdS with two different morphologies (nanosheet (NS) and nanowire (NW)) and found the CdS-NS showed much higher photocatalytic activity for converting the benzyl alcohol than the CdS-NW, but the selectivity to benzaldehyde over the two supports was very low. By depositing Au25 nanoclusters on the CdS-NW and CdS-NS, the morphology effect of the CdS support could be mitigated and their catalytic activity and selectivity could be greatly boosted for the photocatalytic anaerobic dehydrogenation of benzyl alcohol to benzaldehyde and H2. The results of this work would provide new insight into the design of efficient photocatalysts for synthesizing fine chemicals.

Research Progress on Propylene Preparation by Propane Dehydrogenation.

At present, the production of propylene falls short of the demand, and, as the global economy grows, the demand for propylene is anticipated to increase even further. As such, there is an urgent requirement to identify a novel method for producing propylene that is both practical and reliable. The primary approaches for preparing propylene are anaerobic and oxidative dehydrogenation, both of which present issues that are challenging to overcome. In contrast, chemical looping oxidative dehydrogenation circumvents the limitations of the aforementioned methods, and the performance of the oxygen carrier cycle in this method is superior and meets the criteria for industrialization. Consequently, there is considerable potential for the development of propylene production by means of chemical looping oxidative dehydrogenation. This paper provides a review of the catalysts and oxygen carriers employed in anaerobic dehydrogenation, oxidative dehydrogenation, and chemical looping oxidative dehydrogenation. Additionally, it outlines current directions and future opportunities for the advancement of oxygen carriers.

Porous single crystal niobium nitride and tantalum nitride nanocubes boost catalytic performance

Here, we have grown hexahedral porous nitride microcrystals and have confirmed their high catalytic activity and stability when performing the anaerobic dehydrogenation of ethane.

Photocatalyst: To Be Dispersed or To Be Immobilized? The Crucial Role of Electron Transport in Photocatalytic Fixed Bed Reaction.

Photocatalytic fixed bed reactors allow a straightforward separation from the process stream and simplify the installation and operation in practical application. However, it is widely believed that the restriction on mass transport and volume activation severely slows the reaction. Here, we demonstrate that photocatalytic fixed bed reactors can deliver a superior reaction rate to the slurry suspension by rationally modulating the electronic process and the most concerning issue of mass transport occurring on a decisecond time scale does not retard the reaction. Although the long-distance transport of photogenerated electrons in porous semiconductor films toward catalytic sites encounters boundary scattering, this electronic process can be far faster than semiconductor-cocatalyst interfacial electron transfer occurring on the decisecond-second time scale. Besides, the fixed bed reaction can be freely amplified without losing photon utilization. Under irradiation provided by a 320 W Hg lamp, we realize a reaction rate of 0.262 mol/h with 65.2% quantum yield for anaerobic dehydrogenation of ethanol.

Photocatalytic Anaerobic Dehydrogenation of Alcohols over Metal Halide Perovskites: A New Acid-Free Scheme for H2 Production.

Photocatalytic H2 evolution from haloid acid (HX) solution by metal halide perovskites (MHPs) has been intensively investigated; however, the corrosive acid solution severely restricts its practical operability. Therefore, developing acid-free schemes for H2 evolution using MHPs is highly desired. Here, we investigate the photocatalytic anaerobic dehydrogenation of alcohols over a series of MHPs (APbX3, A = Cs+, CH3NH3+ (MA), CH(NH2)2+ (FA); X = Cl-, Br-, I-) to simultaneously produce H2 and aldehydes. Via the coassembly of Pt and rGO nanosheets on MAPbBr3 microcrystals, the optimal MAPbBr3/rGO-Pt reaches a H2 evolution rate of 3150 μmol g-1 h-1 under visible light irradiation (780 nm ≥ λ ≥ 400 nm), which is more than 105-fold higher than pure MAPbBr3 (30 μmol g-1 h-1). The present work not only brings new ample opportunities toward photocatalytic H2 evolution but also opens up new avenues for more effective utilization of MHPs in photocatalysis.

Antimicrobial properties of pristine and Pt-modified titania P25 in rotating magnetic field conditions

Effective and cheap water purification is one of the most important tasks facing humanity. Among various methods of water treatment, heterogeneous photocatalysis is probably most recommended. However, the application of artificial sources of irradiation results in high investment and operating costs. Accordingly, either vis-responsive photocatalysts or different ways of photocatalyst activation should be developed. In the present study, rotating magnetic field (RMF) has been tested to inactivate gram-positive (Staphylococcus epidermidis) and gram-negative (Escherichia coli) bacteria in the presence of pristine and Pt-modified titania P25 photocatalyst. Liquid cultures of the bacteria have been exposed to the titania and RMF (RMF frequency of 1–50 Hz, RMF magnetic induction of ca. 19.92 mT, 180 min exposure time, temperature of incubation at 37 °C). It has been found that highly active titania photocatalyst might also work in the absence of photoirradiation but under RMF. Moreover, its modification with platinum besides highly improved photocatalytic activity (tested for two model reactions of oxidative decomposition of acetic acid and anaerobic dehydrogenation of methanol under UV/vis irradiation) results in significant enhancement of antimicrobial effect under RMF. Additionally, photocatalysts with larger content of oxidized forms of platinum show higher antimicrobial activity, and thus it is proposed that platinum oxides are more active than zero-valent platinum under RMF. This study provides evidence of antimicrobial effect of titania without photoirradiation, indicating that RMF might efficiently activate photocatalyst.

Highly Efficient Dehydrogenation of 2,3-Butanediol Induced by Metal–Support Interface over Cu-SiO2 Catalysts

In the present work, Cu–SiO2 catalysts were synthesized by the modified one-pot hydrothermal strategy and employed in the anaerobic dehydrogenation of 2,3-butanediol to clarify the specific dehydro...

Synergic catalysis by a CuO-like phase and Cu0 for anaerobic dehydrogenation of 2,3-butanediol

This paper describes an emerging synthetic route for acetoin production via the anaerobic dehydrogenation of 2,3-butanediol to give a deep understanding of the specific dehydrogenation behavior of diols. Cu/SBA-15-x-T prepared by the ammonia evaporation method was applied to the dehydrogenation of 2,3-butanediol. The results of XRD, FTIR, H2-TPR, XPS, and NH3-TPD characterization verified that the CuO-like phase, with a Cu2+O2− pair, existed in the form of -Si-O-Cu-O-Si- structures in Cu/SBA-15-x-T catalysts. The amounts of the CuO-like phase and Cu0 can be tuned simultaneously by adjusting the synthetic solution alkalinity and reduction temperature to achieve an optimal synergic effect between the CuO-like phase and Cu0 sites. Compared with the catalytic inertness of Cu catalysts prepared by the conventional impregnation method, the resulting Cu/SBA-15-10.0-300 showed superior catalytic performance (reaction rate: 9.90 × 10−3 mol·min−1g−1) in 2,3-butanediol dehydrogenation. Studies on the structure–performance correlation based on the kinetic study revealed that the catalytic activity of Cu/SBA-15-x-T catalysts is attributable to synergic catalysis between the interfacial CuO-like phase and Cu0 sites, which favors the bond cleavage of O-H and α-C-H, respectively.

Influence of Semiconductor Morphology on Photocatalytic Activity of Plasmonic Photocatalysts: Titanate Nanowires and Octahedral Anatase Nanoparticles.

Octahedral anatase particles (OAP) with eight exposed and thermodynamically most stable (101) facets were prepared by an ultrasonication-hydrothermal (US-HT) reaction from potassium titanate nanowires (TNW). The precursor (TNW) and the product (OAP) of US-HT reaction were modified with nanoparticles of noble metals (Au, Ag or Pt) by photodeposition. Samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), scanning transmission electron microscopy (STEM) and time-resolved microwave conductivity (TRMC). The photocatalytic activity was investigated in three reaction systems, i.e., anaerobic dehydrogenation of methanol and oxidative decomposition of acetic acid under UV/vis irradiation, and oxidation of 2-propanol under vis irradiation. It was found that hydrogen liberation correlated with work function of metals, and thus the most active were platinum-modified samples. Photocatalytic activities of bare and modified OAP samples were much higher than those of TNW samples, probably due to anatase presence, higher crystallinity and electron mobility in faceted NPs. Interestingly, noble metals showed different influence on the activity depending on the semiconductor support, i.e., gold-modified TNW and platinum-modified OAP exhibited the highest activity for acetic acid decomposition, whereas silver- and gold-modified samples were the most active under vis irradiation, respectively. It is proposed that the form of noble metal (metallic vs. oxidized) as well as the morphology (well-organized vs. uncontrolled) have a critical effect on the overall photocatalytic performance. TRMC analysis confirmed that fast electron transfer to noble metal is a key factor for UV activity. It is proposed that the efficiency of plasmonic photocatalysis (under vis irradiation) depends on the oxidation form of metal (zero-valent preferable), photoabsorption properties (broad localized surface plasmon resonance (LSPR)), kind of metal (silver) and counteraction of “hot” electrons back transfer to noble metal NPs (by controlled morphology and high crystallinity).

Promotion effect of nickel for Cu–Ni/γ-Al2O3 catalysts in the transfer dehydrogenation of primary aliphatic alcohols

Cu–Ni/γ-Al2O3 bimetallic catalysts were developed for anaerobic dehydrogenation of non-activated primary aliphatic alcohols to aldehydes. Systematic investigation about the promotion effect of nickel on the catalytic performance was carried out. Hydrogenation of C=C bond rather than C=O bond, was significantly improved over Cu–Ni/γ-Al2O3 catalyst by introducing nickel, which interprets the good conversion of primary aliphatic alcohols. This work would contribute to design new catalysts for dehydrogenation of primary aliphatic alcohols.

Enhanced photocatalytic activity of octahedral anatase particles prepared by hydrothermal reaction

Octahedral anatase particles (OAPs) were prepared by hydrothermal reaction (HT) with various experimental conditions, including different amounts of titanate nanowires (TNWs), different water volumes and different pH values, to obtain products with high contents of OAPs. The properties of photocatalysts were investigated by XRD, SEM, TEM, XPS and time-resolved microwave conductivity (TRMC). Photocatalytic activities for oxidative decomposition of acetic acid (CO2 system) and anaerobic dehydrogenation of methanol (H2 system) were tested. It was found that a larger amount and concentration of TNWs, as well as higher pressure during HT, resulted in the formation of smaller crystallites with higher density of mobile electrons. Enhanced photocatalytic activity, achieved for samples with the best morphology (higher content of OAPs), correlated with slower TRMC signal decay, i.e., slower recombination of charge carriers (e−/h+) probably due to lower content of deep electron traps. It was found that properties of platinum nanoparticles, deposited in-situ in the H2 system in the absence or presence of pre-sparged oxygen, and their connection with OAPs were decisive factors for photocatalytic activity.

Dehydrogenation of primary aliphatic alcohols to aldehydes over Cu-Ni bimetallic catalysts

The catalytic conversion of non-activated primary aliphatic alcohols to aldehydes is a challenge, and monometallic Cu-based catalysts loaded on different supports have often been used for these reactions. Cu-Ni/γ-Al2O3 bimetallic catalysts were prepared and used for anaerobic dehydrogenation of 3,3-dimethyl-1-butanol to 3,3-dimethyl-1-butanal. These catalysts exhibited higher activity than Cu/γ-Al2O3 under the same reaction conditions, and a wide range of primary aliphatic alcohols were efficiently converted to the corresponding aldehydes over Cu-Ni/γ-Al2O3 under mild conditions.

Gas-phase Oxidation of Alcohols with O2 and N2O Catalyzed by Au/TiO2: A Comparative Study

Gas-phase oxidation of alcohols (EtOH, PrOH, i-PrOH, BuOH) to their carbonyl derivatives was used as test reaction to elucidate the mechanism of a low-temper- ature catalytic activity of Au/TiO2. The reactions were carried out in the presence of molecular oxygen, nitrous oxide as well as in the absence of the gas-phase oxidants. The relative contribution of oxidative and non-oxidative dehydrogenation pathways was thus estimated. The pre- sence of oxygen in the feed brought about to a double peak profile of catalytic activity as a function of temperature for all the alcohols. The low-temperature peak fells on 120-130 C. In contrast, the use of N2O as an oxidant gave rise to usual profile of catalytic activity, which is similar to that of anaerobic dehydrogenation of alcohols. The results obtained allowed to suggest the mechanism of the alcohols oxidation. The low temperature peak is probably related to participation of active oxygen species, generated from O2 on the catalyst surface. Oxidation with N2O is interpreted by preliminary dehydrogenation of alcohols to corre- sponding carbonyl derivatives followed by H2 oxidation.

Aldehyde‐Catalyzed Transition Metal‐Free Dehydrative β‐Alkylation of Methyl Carbinols with Alcohols

AbstractDifferent to the borrowing hydrogen strategy in which alcohols were activated by transition metal‐catalyzed anaerobic dehydrogenation, the direct addition of aldehydes was found to be an effective but simpler way of alcohol activation that can lead to efficient and green aldehyde‐catalyzed transition metal‐free dehydrative C‐alkylation of methyl carbinols with alcohols. Mechanistic studies revealed that the reaction proceeds via in situ formation of ketones by Oppenauer oxidation of the methyl carbinols by external aldehydes, aldol condensation, and Meerwein–Ponndorf–Verley (MPV)‐type reduction of α,β‐unsatutated ketones by substrate alcohols, affording the useful long chain alcohols and generating aldehydes and ketones as the by‐products that will be recovered in the next condensation to finish the catalytic cycle.

Green and Scalable Aldehyde‐Catalyzed Transition Metal‐Free Dehydrative N‐Alkylation of Amides and Amines with Alcohols

AbstractIn contrast to the borrowing hydrogen‐type N‐alkylation reactions, in which alcohols were activated by transition metal‐catalyzed anaerobic dehydrogenation, the addition of external aldehydes was accidentally found to be a simple and effective protocol for alcohol activation. This interesting finding subsequently led to an efficient and green, practical and scalable aldehyde‐catalyzed transition metal‐free dehydrative N‐alkylation method for a variety of amides, amines, and alcohols. Mechanistic studies revealed that this reaction most possibly proceeds via a simple but interesting transition metal‐free relay race mechanism.

Generation of Reactive Oxygen Species on Au/TiO2 after Treatment with Hydrogen: Testing the Link to Ethanol Low‐Temperature Oxidation

The gold catalyzed aerobic oxidation of alcohols is currently of great interest for the following reasons: 1) biomass-derived alcohols are a promising, renewable organic feedstock; 2) they use cheap, green oxidants, such as molecular oxygen (air) ; and 3) gold catalysts show extraordinarily high activities under mild conditions. The mechanistic aspects of gold catalyzed oxidation reactions of CO, H2, and other small molecules have been extensively studied, but a generally accepted oxidation mechanism for alcohols under similar conditions has not yet been formulated (however, see references [7–10]). Notably, the efficient low-temperature (50–120 8C) gold catalyzed oxidation of alcohols is known to proceed only in the liquid phase during the course of a long-term batch reaction with high oxygen pressure or intensive O2 flow. [1–4] On the other hand, we recently found that metallic gold nanoparticles supported on TiO2 gave rise to “double peak” catalytic activity in the gasphase oxidation of ethanol to acetaldehyde. The temperature, at which the first peak of activity occurred, 120 8C, was unusually low for the gas-phase reaction of primary alcohols. In contrast, gold supported on Al2O3 and SiO2 showed more usual behaviors, which were analogous to the second peak activity of Au/TiO2 at temperatures above 200 8C. [11] To account for these results, we proposed that specific active oxygen species form on the Au/TiO2 surface under mild reaction conditions and suggested hydrogen as a probable cofactor in their generation. Indeed, H2 can be produced concurrently as a result of ethanol anaerobic dehydrogenation and can thus participate in catalytic activity. In the present work, our efforts were focused on the role of hydrogen in the catalytic activity of gold supported on TiO2, Al2O3, and SiO2 matrixes to provide insights into the different profiles of ethanol oxidation. For this purpose, the O2 isotope exchange technique was applied in order to estimate the relative activity of the surface oxygen species. Oxygen isotope exchange (OIE) is a very sensitive direct method for evaluating the reactivity of surface oxygen atoms, which is a subject of primary interest in heterogeneous oxidation catalysis. Usually, as in the case of metal oxides, OIE is observed at 220–700 8C, although some metal oxides induce OIE at low temperatures after calcination and cooling in a vacuum. A highly reactive oxygen species, so called aoxygen, is generated on the Fe-ZSM5 zeolite surface after treatment with N2O. These species readily oxidize organics (benzene, methane, etc.) as well as perform OIE at room temperature. A special but relevant case, although photoinduced, is the OIE over TiO2, which also occurs at room temperature due to the involvement of reactive oxygen species, probably O anion radicals. Notably, a correlation was found between the TiO2 activity for the photoinduced OIE and the oxidation of isobutane, methanol, and ethanol over TiO2 upon ultraviolet (UV) irradiation. Generally, in a heterophase system comprising molecular dioxygen (O2) in the gas phase and oxygen on the surface of a solid (O), two isotope exchange reactions take place: 1) the hetero-exchange reaction [Equation (1)] , which is conveniently monitored by a fraction of the O isotope in the gas phase (a), and 2) the homo-exchange reaction [Equation (2)] , which is monitored by the parameter y = *C34 C34 (the difference between the equilibrium (*C34) and the current (C34) values for the fraction of asymmetric isotopic OO molecules). Obviously, the low-temperature activity of a catalyst in an oxygen homoexchange can indicate the involvement of very active surface oxygen species by analogy with the cases of a-oxygen and illuminated TiO2. [17]

Discovery and Mechanistic Studies of a General Air-Promoted Metal-Catalyzed Aerobic N-Alkylation Reaction of Amides and Amines with Alcohols

The thermodynamically unfavorable anaerobic dehydrogenative alcohol activation to aldehydes and hydridometal species is found to be the bottleneck in metal-catalyzed N-alkylations due to a general and unnoticed catalyst deactivation by amines/amides. Thus, different from the anaerobic dehydrogenation process in borrowing hydrogen or hydrogen autotransfer reactions that require noble metal complexes or addition of capricious ligands for catalyst activation, the water-producing, exothermic, metal-catalyzed aerobic alcohol oxidation is thermodynamically more favorable and the most effective and advantageous aldehyde generation protocol. This leads to a general and advantageous air-promoted metal-catalyzed aerobic N-alkylation methodology that effectively uses many simpler, less expensive, more available, and ligand-free metal catalysts that were inactive under typical anaerobic borrowing hydrogen conditions, avoiding the use of preformed metal complexes and activating ligands and the exclusive requirement of inert atmosphere protection. This aerobic method is quite general in substrate scope and tolerates various amides, amines, and alcohols, revealing its potentially broad utilities and interests in academy and industry. In contrast to the commonly accepted borrowing hydrogen mechanism, based on a thorough mechanistic study and supported by the related literature background, a new mechanism analogous to the relay race game that has never been proposed in metal-catalyzed N-alkylation reactions is presented.

On the Active Oxygen in Bulk MoO3 during the Anaerobic Dehydrogenation of Methanol

The oxidation of methanol under anaerobic reaction conditions over MoO3 has been studied using an in situ approach, combining ultraviolet−visible (UV−vis), Raman, wide-angle X-ray scattering (WAXS)...