Dehydrogenation Step Research Articles

Research advances in branched-chain amino acid metabolism in tumors.

The metabolic reprogramming of amino acids is an important component of tumor metabolism. Branched-chain amino acids (BCAAs) perform important functions in tumor progression. They are the important amino donor and are involved in the synthesis of various non-essential amino acids, nucleotides, and polyamines to satisfy the increased demand for nitrogen sources. This review summarizes the studies related to abnormalities in BCAA metabolism during tumorigenesis and the potential therapeutic targets. The expression of BCAA transporters was significantly upregulated in tumor cells, which increases BCAA uptake. High expression of the BCAA transaminases is prevalent in various tumors, however, the dehydrogenation step of BCAA catabolism is inhibited in tumors. This review shows that BCAA metabolic reprogramming is an important tumor metabolic feature, and metabolic genes of BCAAs play a crucial role in tumor metabolism, representing a good auxiliary target for early clinical diagnosis and treatment. In addition, BCAAs are indispensable for maintaining immune system function, and dietary supplementation with BCAAs can enhance the activity of immune cells. Therefore, BCAA supplementation in tumor patients may affect the interaction between the immune system and tumors.

Methanolation of Olefins: Low-Pressure Synthesis of Alcohols by the Formal Addition of Methanol to Olefins.

Methanolation of olefins is introduced as a new low-pressure synthetic pathway to C1 elongated alcohols. Formally, H3COH is added to the C=C bond in a 100% atom efficient manner. Mechanistically, the overall transformation occurs as a tandem reaction sequence by combining the dehydrogenation of methanol to syngas at a CO:H2 ratio of 1:2 with subsequent hydroformylation to the corresponding aldehyde and its final hydrogenation to the alcohol. The dehydrogenation and hydrogenation steps are catalysed by a Mn/pincer complex, while the hydroformylation is accomplished by a Rh/phosphine catalyst. Using 1-octene as prototypical substrate, a yield of 80% nonanol was achieved with a ratio of 93:7 of linear to branched alcohols and turnover numbers (TONRh) of more than 17 000 could be obtained in relation to the precious metal Rhodium. The integrated catalytic system provides direct access to alcohols from olefins and "green" methanol, avoiding the handling of pressurized CO and H2 and the use of specialized high-pressure equipment as the process conditions do not exceed 10 bar with partial pressures of syngas in the range of only 1-2 bar.

CO2-free production of hydrogen via pyrolysis of natural gas: influence of non-methane hydrocarbons on product composition, methane conversion, hydrogen yield, and carbon capture

Methane pyrolysis represents a CO2-free hydrogen production route that enables simultaneous carbon capture. While the majority of previous studies in the field focus on pure CH4 as feed gas stream, commercial processes will typically rely on natural gas as feedstock that contains also non-methane hydrocarbons such as ethane, propane, and n-butane. Therefore, the present study evaluates how CH4 conversion, H2 selectivity, product composition, and solid carbon yield evolve when using either pure CH4 or synthetic natural gas (SNG) as feed gas stream for a thermal pyrolysis process in a lab-scale high-temperature reactor. For this, industrially viable conditions are applied, namely temperatures between 1000 °C and 1600 °C, residence times between 1 s and 7 s, and molar H2 dilution ratios between 1:1 and 4:1. Although the use of SNG results in slightly lower hydrocarbon conversions because the additional components in SNG result in a higher effective H2 dilution ratio compared to a CH4-only feed, the non-methane hydrocarbons in the SNG have a positive effect on both H2 selectivity and solid carbon yield. Taking existing mechanistic understanding into account, these positive effects are attributed to radicals formed from the non-methane hydrocarbons, which facilitate dehydrogenation steps from ethane to ethylene and hereby increase the relative amount of H2 originating from CH4. The introduction of a carbonaceous fixed bed further benefits the performance of the pyrolysis process and ultimately enables to capture more than 98% of carbon in its solid form under industrially viable process conditions.

Rationally Designed L12-Pt2RhFe Intermetallic Catalyst with High CO-Tolerance for Alkaline Methanol Electrooxidation.

It is a grand challenge to deep understanding of and precise control over functional sites for the rational design of highly efficient catalysts for methanol electrooxidation. Here, an L12-Pt2RhFe intermetallic catalyst with integrated functional components is demonstrated, which exhibits exceptional CO tolerance. The Pt2RhFe/C achieves a superior mass activity of 6.43 A mgPt -1, which is 2.23-fold and 3.53-fold higher than those of PtRu/C and Pt/C. Impressively, the Pt2RhFe/C exhibits a significant enhancement in durability owing to its high CO-tolerance and stability. Density functional theory calculations reveal that high performance of Pt2RhFe intermetallic catalyst arises from the synergistic effect: the strong OH binding energy (OHBE) at Fe sites induce stably adsorbed OH species and thus facilitate the dehydrogenation step of methanol via rapid hydrogen transfer, while moderate OHBE at Rh sites promote the formation of the transition state (Pt-CO···OH-Rh) with a low activation barrier for CO removal. This work provides new insights into the role of OH binding strength in the removal of CO species, which is beneficial for the rational design of highly efficient catalysts.

Non‐Oxidative Dehydroaromatization of Linear Alkanes on Intermetallic Nanoparticles

AbstractThere has been significant interest in developing new catalytic systems to convert linear chain alkanes into olefins and aromatics. In the case of higher alkanes (≥C6), the production of aromatic compounds such as benzene‐toluene‐xylenes is highly desirable. However, as the length of the carbon chain increases, the dehydrogenation process becomes more complex, not only due to the challenges of C−H activation but also the need for selectivity towards the desired products by the possibility of side reactions such as isomerization and cracking. Here, we present a detailed analysis of the dehydroaromatization of n‐hexane, n‐heptane, and n‐octane, using PtSn intermetallic nanoparticles supported on SBA‐15 as the catalyst. Through in situ spectroscopic and kinetic analysis, we have probed the reaction kinetics and catalyst deactivation, and provided a mechanistic understanding of the dehydroaromatization process on the surface of the PtSn intermetallic nanoparticles. Introducing Sn has been shown to be crucial not only for enhancement of catalytic activity, but also for higher aromatics selectivity and stability on stream. Furthermore, the analysis of dehydroaromatization reaction rates of reactant and possible intermediates indicates that the dehydroaromatization of n‐hexane to benzene likely proceeds through initial dehydrogenation steps followed by ring closing.

Evolution of Nitrogen-Coordinated Metal Single Atoms Toward Single-Atom Alloys on MgH₂ as Efficient and Stable Hydrogen Spillover Catalysts.

M-N-C catalysts with nitrogen-coordinated metal single-atom active sites have demonstrated high activity for hydrogen storage materials, but their stability in this application remains uncertain. This study addresses this issue by using nickel phthalocyanine (NiPc) molecules on MgH₂ particles as a model system. It is found that the N-coordinated high-valence Ni single atoms in the NiN₄ active site are unstable in the reducing environment of hydrogen storage, spontaneously evolving into zero-valence Ni, forming a Ni₁-Mg single-atom alloy (SAA). The Ni₁-Mg SAA exhibits remarkable stability in catalyzing Mg hydrogen storage reactions. Furthermore, it demonstrates comprehensive catalytic activity for each step of hydrogen absorption and desorption from Mg, surpassing the efficiency of the NiN₄ active site, especially in the critical steps of hydrogenation and dehydrogenation. Overall, the catalytic performance of Ni₁-Mg SAA is superior to most known nickel-based catalysts. This evolutionary process is also observed in FePc, CoPc, and tetraphenylporphyrin nickel (Ni-TPP), suggesting that this reducing transformation is a universal phenomenon for MN₄-type active sites in hydrogen storage catalysis.

Can ZnO/Cu catalyst provide promising activity for glycerol direct dehydrogenation? A combined density functional theory and coverage-dependent microkinetics study

Non-oxidative dehydrogenation (NODH) reaction of glycerol is a perfect atom economical technical route to produce higher-value 1,3-dihydroxyacetone (DHA). Cu-based catalyst (especially ZnO/Cu system), is known as active species for alcohol dehydrogenation, which may be also promising one for glycerol NODH. In this study, we combine coverage-dependent free energy profile using first-principle calculation, and microkinetic model, to investigate the NODH of glycerol on the ZnO/Cu(111) surface, and a detailed comparison is made with Cu (111) surface. The coverage-dependent microkinetic model takes into account the lateral adsorbate–adsorbate self-interactions and cross-interactions, and their effect on binding energy of both intermediate and transition state. Besides, it guarantees the reaction kinetics is based on the coverage self-consistent between surface model and microkinetic result under practically reaction conditions. Compared with coverage-dependent kinetics simulation (20 %–30 %), coverage-independent model overestimates the DHA selectivity on Cu (111) (over 90 %). Our coverage-dependent kinetics simulation illustrates that both glycerol conversion and DHA selectivity are most determined by the first dehydrogenation step (OH bond scission) of glycerol on Cu (111). However, when ZnO cluster adsorbed on the Cu (111) surface, ZnO cluster promotes the electron transferring between glycerol and Cu sites, which accelerates OH bond scission process of glycerol. Under coverage-dependent microkinetic model, the turnover frequency and selectivity of DHA on ZnO/Cu(111) get much improvement compared with Cu (111). Finally, the superior of ZnO/Cu(111) is further proved by continuous stirred tank reactor simulation, where NODH of glycerol need shorter residence times or lower temperature to reach 100 % conversion, as well as keep higher DHA selectivity.

Producing Hydrogen with Less Energy in Ammonia Electrolyzer Stack Using Pt-Ir Catalyst Dual-Layer Electrode

Electrochemical ammonia decomposition has recently been regarded as a possible future technology for CO2-free hydrogen production. Pt-based catalysts have already known for having excellent activity in ammonia oxidation reactions (AOR) due to the fast dehydrogenation step enabled by the moderate adsorption strengths of nitrogen species [1]. Among them, the incorporation of Ir into Pt notably decreases the activation energy required for ammonia oxidation on Pt, lowing onset potential in alkaline media [2]. Besides, the electrolysis of ammonia has a less energy consumption than water electrolysis because of the lower operating voltage at the Anode [3]. In this study, we fabricated dual-layer electrode containing Pt-Ir catalyst, enhancing the AOR catalytic activity and showing long-term stability. The ammonia electrolysis single-cell with an anion exchange membrane (AEM) was successfully operating and then scaled up to a large area stack cell. We observed that this electrolyzer stack cell produced high-purity hydrogen using less energy than water electrolysis.AcknowledgementsThis research was supported by National R&D Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (NRF-2021K1A4A8A01079455). This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) [No. 2021R1A5A1028138].Reference[1] J. Liu, Z. Liu, Adv. Funct. Mater 2022, 32, 2110702[2] A. Estejab, G. G. Botte, Comput. Theor. Chem 2016, 1091, 31-40[3] J. Gwak, M. Choun, ChemSusChem 2016, 9, 403–408

Ba promoter effect on cobalt-catalyzed ammonia decomposition kinetics: A theoretical analysis

Ammonia decomposition is a key reaction in the context of hydrogen storage, transport, and release. This study combines density functional theory (DFT) calculations with microkinetic modeling to address the promotion mechanism of Ba species for ammonia decomposition on Co catalysts. The modified adsorption properties of Co upon the addition of metallic Ba or BaO suggest that the promoters play a role in alleviating the competitive adsorption of H. Calculating the full reaction pathway of ammonia decomposition shows that limiting the investigation to the N–N association step, as done previously, overlooks the effect of the promoter on the energy barriers of the NHx dehydrogenation steps. Challenges of modeling the ammonia decomposition reaction are addressed by understanding that the NH2 intermediate is stabilized on the step sites rather than the terrace sites. When the effect of H-coverage on the adsorption of NH3 is not considered in the microkinetic simulations, the results conflict with the experiments. However, accounting for the effect of H-coverage, as performed here, shows that BaO-doped Co has higher rates than pristine Co and Ba-doped Co at the reaction temperature of 723.15 K. When H is adsorbed on the Ba-doped Co, the adsorption of ammonia becomes significantly endergonic, which makes the rates relatively slow. The superiority of the BaO-promoted catalyst is attributed to a lower energy for the transition state of the rate-determining step, coupled with a reduced impact of the hydrogen coverage on weakening the ammonia adsorption. The kinetic analysis of the influence of Ba and BaO on the Co surface shows that BaO-doped Co aligns more closely with experimental observations than Ba-doped Co. This implies that Ba on the Co surface is likely to be in an oxide form under reaction conditions. Understanding the kinetics of the ammonia decomposition reaction provides a foundation for developing highly effective catalysts to accelerate the industrial utilization of ammonia as a sustainable hydrogen carrier.

Direct coupling of CH4 and CO2 into acetic acid over CuPdO2/Al2O3 in the presence of H2O2

Direct conversion of methane and carbon dioxide into acetic acid is a dream way to address the two greenhouse gases, but is challenged by their chemical inertness. Cu and Pd are promising candidates both in CH4 and CO2 activation as well as the subsequent C-C coupling reactions at low temperature. Herein, we report that acetic acid can be produced by the direct coupling of CH4 and CO2 in the presence of H2O2 over Cu-Pd/Al2O3 catalysts at 50 °C. Results show that the acetic acid yield reaches 48.1 μmol·gcat−1·h−1 on the optimized reaction condition over Cu3.8-Pd1.6/Al2O3 catalyst, which is higher than that of either mono-Cu or mono-Pd catalyst. Extensive characterization indicates the higher activity of Cu3.8-Pd1.6/Al2O3 catalyst is attributed to the strong synergistic effect between Cu and Pd, which results in the formation of CuPdO2 phase, and thus promoting the electron transfer from Cu to Pd. DRIFTS experiments reveal that acetic acid is produced by the coupling of CH3* and COOH* over CuPdO2 active sites via Langmuir-Hinshelwood mechanism, where CH3* is originated from CH4 dehydrogenation step, and COOH* may formed by the activation of CO2 by H2O2. This study provides a new approach for the co-conversion of CH4 and CO2 into acetic acid at low temperature.

A deeper orbital hybridization because of more unpaired electrons in d orbital resulted in a better catalytic performance

Previous reports usually co-doping various additional transition metals to improve the NH3-SCR performance of V/TiO2 catalyst. However, seldom work understood the so-called enhancement from an atom scale. This work first selected nine elements (Me) mainly from a same VIB family or a same fourth period, and compared them in transition states of MeV/TiO2 during NH3-SCR. The dehydrogenation step of adsorbed NH3 resulted to be the key step and W substitution got the lowest dehydrogenation energy of 1.29 eV. After estimating the key atoms, the total width of Me-O-V hybridization followed the order of 1.7 eV (WV/TiO2) > 1.3 eV (V/TiO2) > 1.1 eV (CoV/TiO2) > 0.9 eV (LaV/TiO2). The deeper hybridization was attributed to a shorter Me-O-V bond. Both V and W were in a high-spin state while Co and La were in a low-spin state. Moreover, W atom had four semi full d orbitals, bigger than that (three) of V, which were more conducive to electron transfer, and resulting in the biggest overlapping of atomic orbitals. The above prediction was consistent with the afterward experimental result, in which MeV/TiO2 showed a NH3-SCR conversion order of 81 % (WV/TiO2) > 59 % (V/TiO2) > 41 % (CoV/TiO2) > 2 % (LaV/TiO2) at 300 °C. The main result of this work is in favor of designing an effective catalyst from the atom scale.

Deciphering reaction mechanism network of n-heptane dehydrocyclization over H-ZSM-5 zeolite

The dehydrocyclization of naphtha is a process of great significance in the petrochemical industry, as it enables the production of valuable aromatics. While experimental studies have demonstrated the catalytic activity of H-ZSM-5 zeolite in converting alkanes to aromatics, there is a notable absence of theoretical investigations into the reaction mechanisms involved in the dehydrocyclization of naphtha. Herein, the conversion of n-heptane to toluene over H-ZSM-5 zeolite was examined using first-principles density functional theory (DFT) calculations. The dehydrocyclization process of n-heptane involves several key steps, including dehydrogenation, isomerization, and cyclization. Specifically, the dehydrogenation of n-heptane produces 1-heptene, 2-heptene, and 3-heptene, which then undergo various dehydrocyclization pathways leading to the formation of toluene: (i) C1-C5 ring closure of 1-heptene; (ii) C1-C6 ring closure of 1-heptene; (iii) C2-C6 ring closure of 2-heptene; (iv) dehydrogenation of 3-heptene to heptadiene, with C1-C5 ring closure; and (v) dehydrogenation of 3-heptene to heptatriene, with C1-C6 ring closure, followed by sequential ring expansion and/or dehydrogenation to toluene. The DFT results indicate that the dehydrogenation steps are energetically demanding, with the conversion of n-heptane to toluene via 1-heptene identified as the most favorable cyclization route. This theoretical investigation provides valuable insights into the fundamental mechanisms underlying the dehydrocyclization of naphtha for the production of aromatics, with potential implications for the development of more efficient catalytic processes in the petrochemical industry.

Heterostructured Pt-PbS Nanobelt Achieves Remarkable Direct Formic Acid Oxidation Catalysis.

Developing efficient and CO-tolerant platinum (Pt)-based anodic catalysts is challenging for a direct formic acid fuel cell (DFAFC). Herein, we report heterostructured Pt-lead-sulfur (PtPbS)-based nanomaterials with gradual phase regulation as efficient formic acid oxidation reaction (FAOR) catalysts. The optimized Pt-PbS nanobelts (Pt-PbS NBs/C) display the mass and specific activities of 5.90 A mgPt-1 and 21.4 mA cm-2, 2.2/1.2, 1.5/1.1, and 36.9/79.3 times greater than those of PtPb-PbS NBs/C, Pt-PbSO4 NBs/C, and commercial Pt/C, respectively. Simultaneously, it exhibits a higher membrane electrode assembly (MEA) power density (183.5 mW cm-2) than commercial Pt/C (40.3 mW cm-2). This MEA stably operates at 0.4 V for 25 h, demonstrating a competitive potential of device application. The distinctive heterostructure endows the Pt-PbS NBs/C with optimized dehydrogenation steps and resisting the CO poisoning, thus presenting the remarkable FAOR performance. This work paves an effective avenue for creating high-performance anodic catalysts for fuel cells and beyond.

Unraveling the Mechanism of Ammonia Electrooxidation by Coupled Differential Electrochemical Mass Spectrometry and Surface-Enhanced Infrared Absorption Spectroscopic Studies.

Ammonia electrooxidation has received considerable attention in recent times due to its potential application in direct ammonia fuel cells, ammonia sensors, and denitrification of wastewater. In this work, we used differential electrochemical mass spectrometry (DEMS) coupled with attenuated total reflection-surface-enhanced infrared absorption (ATR-SEIRA) spectroscopy to study adsorbed species and solution products during the electrochemical ammonia oxidation reaction (AOR) on Pt in alkaline media, and to correlate the product distribution with the surface ad-species. Hydrazine electrooxidation, hydroxylamine electrooxidation/reduction, and nitrite electroreduction on Pt have also been studied to enhance the understanding of the AOR mechanism. NH3, NH2, NH, NO, and NO2 ad-species were identified on the Pt surface with ATR-SEIRA spectroscopy, while N2, N2O, and NO were detected with DEMS as products of the AOR. N2 is formed through the coupling of two NH ad-species and then subsequent further dehydrogenation, while the dimerization of HNOad leads to the formation of N2O. The NH-NH coupling is the rate-determining step (rds) at high potentials, while the first dehydrogenation step is the rds at low potentials. These new spectroscopic results about the AOR and insights could advance the search and design of more effective AOR catalysts.

Metal-acid synergistic catalysis accelerates the hydrogen borrowing amination of alcohols by confining Ru sites in Beta zeolite

Direct hydrogen transfer amination of alcohols with amines is an environmentally friendly and atom-economical route for the synthesis of N-alkylamines. Noble metal species are highly catalytic active sites, but the exorbitant price makes the urgency to boost the atom efficiency with stable recyclability. Herein, we demonstrated that encapsulation of Ru nanoparticles (NPs) within BEA zeolite through direct hydrothermal approach greatly promoted the catalytic efficiency in the N-alkylation of aromatic alcohols and amines under additive- and solvent-free conditions, resulting in the high yield (∼93 %), maximum turnover number (TON) of 12,822 and turnover frequency (TOF) of 9012 h−1, with stable recyclability and extendable substrate scope. The kinetic studies and in-situ characterizations revealed that the synergy of confined Ru NPs and adjacent acid sites of BEA zeolite significantly promoted the C–H bond activation in the rate-determining step of alcohol dehydrogenation into aldehydes. Besides, the acid sites also accelerated the condensation of aldehyde intermediates and anilines to promote the kinetic equilibrium, while the moderate strength of the Ru–H bond resulting from the confined Ru NPs is advantageous to balance the dehydrogenation and hydrogenation steps to reach the fascinating H-transfer process.

Depolymerization of lignin over heterogeneous Co-NC catalyst

Green and atom-economic depolymerization of lignin remains a great challenge due to its complex non-repetitive structure and the inert property for chemo-digestion. A redox-neutral lignin depolymerization system without the use of extra oxidant and/or reductant over a Co-NC catalyst has been developed in this work, providing the first non-noble metal heterogeneous catalytic system for redox-neutral valorization of lignin. Mechanistic studies based on control reactions and deuterium labeling experiments suggest that the reaction proceeds via a metal-catalyzed dehydrogenation of Cα-OH to afford a carbonyl intermediate, followed by Cβ-O bond cleavage (via hydrogenolysis) to afford monophenols and aromatic ketone products. The hydrogen used for the cleavage of the Cβ-O bond originates from the alcohol moiety in the substrate, and the cascade dehydrogenation and hydrogenolysis steps are highly coupled, rendering it an efficient and atom-economic process.

Pt/Al2O3 as efficient catalyst for the dehydrogenation of Dodecahydro-N-ethylcarbazole

The use of dodecahydro-N-ethylcarbazole in hydrogen storage for liquid organic hydrogen carrier systems holds potential for achieving large-scale application. In order to investigate the relationship between dodecahydro-N-ethylcarbazole dehydrogenation performance and Pt particles size, a series of monometallic Pt/Al2O3 catalysts with different Pt particles size from 0.70 nm to 5.12 nm were controlled synthesized by a simple impregnation method. The obtained catalysts are systematically characterized via XRD, 27Al MAS NMR, SEM-EDS, TEM, N2-adsorption, CO-IR, H2-TPR and NH3-TPD analyses, which provide essential micro-structure of these catalysts. The dehydrogenation of dodecahydro-N-ethylcarbazole over Pt/Al2O3 is a typical consecutive reaction, which follows a reaction sequence of dodecahydro-N-ethylcarbazole → octahydro-N-ethylcarbazole → tetrahydro-N-ethylcarbazole → N-ethylcarbazole. These dehydrogenation steps are quite sensitive to the Pt particle size. Large Pt particle can greatly enhance the reaction rates in octahydro-N-ethylcarbazole → tetrahydro-N-ethylcarbazole and tetrahydro-N-ethylcarbazole → N-ethylcarbazole steps. However, these two steps are difficult to take place in small Pt particles. The high performance of large Pt particle in dehydrogenation can be ascribed to its highly exposed (111) crystal face. The optimized catalyst Pt5.0/γ-Al2O3 with Pt average size of 4.63 nm demonstrated exceptional performance in dodecahydro-N-ethylcarbazole dehydrogenation at 180 °C and 101 kPa, and the dodecahydro-N-ethylcarbazole conversion of 100 %, N-ethylcarbazole selectivity of 96.44 % and dehydrogenation efficiency of 98.73 % can be achieved. These results provide valuable insights for the development of efficient metal-based catalysts for liquid organic hydrogen carriers hydrogen storage system.

Subnanometric Pt-Ga alloy clusters confined within Silicalite-1 zeolite for n-hexane dehydrogenation

Dehydrogenation of light naphtha followed by catalytic cracking into high-value end products can meet the high demand in the world’s petrochemical market. In this work, at attempting synthesis of novel catalysts for hexane dehydrogenation, a series of bimetallic Pt-Ga clusters encapsulated within Silicalite-1 (S-1) catalysts were synthesized using the ligand-protected direct H2 reduction method. The reduced Pt-Ga@S-1-H catalysts comprised restricted ultra-fine Pt-Ga alloys with an average size 0.86–0.95 nm, mainly corresponding to the Pt3 clusters with coordinate number 1.5–2.1. Ga doping significantly improved the catalytic stability, depending on the Ga content, which ranged from 0.02 to 0.27 wt%. As confirmed by the XPS and EXAFS analysis, after the Ga addition, electron transfer occurred between the Pt-Ga alloys and the skeleton oxygen in zeolite, stabilizing the Pt clusters on the zeolite, thereby inhibiting the growth of Pt crystals. During the n-hexane dehydrogenation, the 0.40Pt0.04 Ga@S-1-H catalyst exhibited a hexene selectivity of 87.1 %, achieving a hexene formation rate of 101.4 molhexene∙gPt-1∙h−1 at 550 °C with a WHSV of 90 h−1. After 1000 min of reaction, this best catalyst experienced only slight deactivation with a deactivation constant of 0.066 h−1. The catalytic activity remained almost unchanged after consecutive five cycles of H2 regeneration. DFT calculation using the synchronous structural models showed that the Gibbs free energy changes (−ΔG) for the first three steps of hexane dehydrogenation over the 0.4Pt0.04 Ga@S-1-H catalyst were much lower than those obtained on the 0.4Pt/S-1-H catalyst, suggesting that the introduction of Ga energetically favored the hexane dehydrogenation.

The Size and Charge Effect of Pt Cluster on the Electrocatalytic Activity Toward the First Step of Dehydrogenation of Methanol

Abstract The O–H/C–H scission of methanol on Pt clusters is a crucial step in direct methanol fuel cells applications. The first dehydrogenation process of methanol on Ptnq clusters (n = 5, 13, 19; q = 0, +1, −1) in various charge states is studied. Our findings indicate that methanol adsorbs more easily on cationic Ptn+ than on neutral Ptn or anionic Ptn−. However, the adsorption capacity of methanol on Ptnq gradually decreases with increasing cluster size, especially for CH3OH on Ptn+, which decreases significantly (from −57.61 kcal/mol to −16.41 kcal/mol). Compared with Ptn and Ptn+, the energy barrier of O–H/C–H bond cleavage is significantly reduced by injecting an electron into Ptn to form Ptn−, and the activity of the catalyst is improved. However, the energy barrier of O–H/C–H cleavage increases gradually with cluster size, leading to a decrease in catalytic activity. The effect of charge weakens as cluster size increases, and small clusters with injected electrons exhibit better catalytic activity.

Influence of Zn species in MWW zeolite on the ethane dehydroaromatization with the assistance of propane co-dehydroaromatization and CO2 reduction

The Zn-containing HMCM-22 samples with different zinc species were prepared and characterized to discriminate the influence of zinc species on the ethane activation by the initial C-H bond cleavage or the β-H cleavage dehydrogenation step of alkyl zinc species (Zn-C2H5) through the propane co-dehydroaromatization and CO2 reduction process. The synergistic effect of zinc species types with the Brønsted acid sites (BAS) of the parent zeolite HMCM-22 had a significant effect on the ethane dehydroaromatization. The synergistic effect between ZnO species and BAS had better ethane conversion and aromatics selectivity in ethane dehydrogenation, while the poor synergistic effect between ZnOH+ species and BAS was not conducive to the formation of aromatics, and ZnOH+ species was more conducive to ethane dehydrogenation. The ZnOH+ has better catalytic performance in CO2 activated ethane and promote the β-H desorption of Zn-C2H5 in ethane dehydrogenation. The synergetic effect of ZnO species and BAS in the zeolite facilitates the hydride transfer activation of ethane by propylene carbenium ions thus enhancing the ethane conversion through ethane-propane co-aromatization.