Alkane Dehydrogenation Research Articles

Laser vaporized CrOx/Al2O3 nanopowders as a catalyst for isobutane dehydrogenation

Laser vaporized xCr/Al2O3 nanopowders with the particle size of ca. 15 nm were studied by XRF, EDX, HRTEM, XRD, DD, BET, TGA, UV–Vis DRS, Raman and PL spectroscopy methods as a catalytic system in dehydrogenation of isobutane. The nanopowders were found to contain not only the Cr6+ ions located on the surface of nanoparticles, but also two different types of Cr3+ sites as components of the γ-Al2O3 solid solution. One type consists of the bulk Cr3+b sites in a strong crystal field. Another type is represented by the Cr3+s sites residing near the surface of xCr/Al2O3 nanoparticles. Such sites are in a weak crystal field. It was shown that catalytic activity of the nanostructured xCr/Al2O3 system is provided by the high content of surface Cr3+s sites. The results obtained make it possible to propose the nanopowders obtained by laser synthesis as a promising catalytic system that can be used in the development of highly active catalysts for dehydrogenation of alkanes with the decreased chromium content.

A Laser-Activated Membrane Introduction Mass Spectrometry Study of Proton Spillover Promoted Alkane Dehydrogenation.

Operando high-throughput evaluation of heterogeneous catalysts by laser-activated membrane introduction mass spectrometry (LAMIMS) elucidates the Pt loading dependence of methylcyclohexane dehydrogenation on platinized γ-alumina beads. A CO2 marking laser rapidly and sequentially heats catalyst beads positioned on a heat-dissipating carbon paper support that overlays a silicone membrane, separating the bead library reaction zone from a quadrupole mass analyzer. The toluene m/z peak varies logarithmically with Pt loading, suggesting that reactivity includes factors that are negatively correlated to Pt loading. These factors may include the Pt/γ-Al2O3 surface interfacial region as one component of a heterogeneous catalytically active surface area/mass. This work demonstrates LAMIMS as a broadly applicable high-throughput operando screening method for heterogeneous catalysts.

Atomic-level understanding on the evolution behavior of subnanometric Pt and Sn species during high-temperature treatments for generation of dense PtSn clusters in zeolites

To achieve high-loading of stable subnanometric metal clusters on solid carriers is a challenge since those small metal clusters have strong tendency to sinter into larger nanoparticles. Development of facile synthesis methodologies to obtain subnanometric metal catalysts with high metal loading and high stability against sintering at high temperature (>500 °C) in reductive atmosphere (such as H2) is critical for the practical applications. In this work, we will present and discuss the generation of high-loading (~1.4 wt%) subnanometric Pt clusters confined in the sinusoidal channels of MFI zeolite, on the basis of the atomic-level understanding on the evolution of Pt and Sn species during high-temperature oxidation–reduction treatments. It will be shown that the structural evolution of Pt and Sn species is dependent on the post-synthesis treatments. The Pt particles on the external surface can disintegrate into subnanometric Pt species and get stabilized in the zeolite channels during high-temperature calcination in air while Sn species migrate from surface region to internal region during high-temperature reduction treatment at 650 °C. The resultant material containing bimetallic PtSn clusters confined in the 10MR sinusoidal channels of the purely siliceous MFI zeolite show excellent catalytic activity and stability, as demonstrated for dehydrogenation of light alkanes at high reaction temperature.

Stable and Selective Dehydrogenation of Methylcyclohexane using Supported Catalytically Active Liquid Metal Solutions – Ga52Pt/SiO2 SCALMS

AbstractThe use of gallium‐rich, Supported Catalytically Active Liquid Metal Solution (SCALMS) is a promising new concept to achieve catalysis with atomically dispersed active metal atoms. Expanding our previous work on short alkane dehydrogenation, we present here the application of SCALMS for the dehydrogenation of methylcyclohexane (MCH) to toluene (TOL) using a Ga52Pt alloy (liquid under reaction conditions) supported on silica. Cycloalkane dehydrogenation catalysis has attracted great attention recently in the context of hydrogen storage concepts using liquid organic hydrogen carrier (LOHC) systems. The system under investigation showed high activity and stable conversion of MCH at 450 °C and atmospheric pressure for more than 75 h time‐on‐stream (XMCH=15 %) with stable toluene selectivity (STOL) of 85 %. Compared to commercially available Pt/SiO2, the SCALMS system resulted in higher yields and robustness. Baseline experiments with Pt‐free Ga/SiO2 under identical conditions revealed the decisive influence of Pt dissolved in the liquid Ga matrix.

Colloidal Synthesis of Well-Defined Bimetallic Nanoparticles for Nonoxidative Alkane Dehydrogenation

Precise synthesis and characterization of bimetallic nanoparticles are critical toward understanding structure–activity relationships in alkane dehydrogenation catalysis. Traditional synthetic meth...

Factors influencing 1,3-butadiene formation for light alkane dehydrogenation

The formation of 1,3-butadiene is detrimental to the steady operation for the alkane dehydrogenation processes, therefore, feasible strategies to inhibit its formation were investigated over Sn-based catalysts. Clearly, most of 1,3-butadiene comes from n-butane dehydrogenation. The formation rate of 1,3-butadiene is closely related to the catalyst compositions, such as the nature of active component and the support. Meanwhile, introducing appropriate promoters can reduce the amount of 1,3-butadiene. For the reaction conditions, to obtain both high yield of n-butenes and low yield of 1,3-butadiene, reaction temperature and n-butane partial pressure should be chosen according to the actual situation. A relatively high weight hourly space velocity can inhibit 1,3-butadiene formation. Besides, the optimal hydrogen partial pressure can be found, and here the appropriate value should be between 10.1 and 20.3 kPa. Finally, according to the reaction behavior, it is hypothesized that 1,3-butadiene is probably formed through both direct dehydrogenation of n-butane and further dehydrogenation of n-butenes.

Toward Concurrent Engineering of the M1-Based Catalytic Systems for Oxidative Dehydrogenation (ODH) of Alkanes

In the oxidative dehydrogenation (ODH) of alkanes, some important advances of the last decade have made it possible to accelerate the development and industrial insertion of the M1 based catalytic systems. These catalysts may be fine-tuned to account for the inevitable variability of different chemicals and impurities in the feedstocks. The latter may include, among others, different blends of shale gases, with different ratios of the C1-C3 alkanes and impurities such as sulfur, phosphorus, etc. In this article, we review the recent progress achieved in our understanding of the crystal structures and the oxidative dehydrogenation (ODH) reaction mechanisms of the multi-metal oxide (MMO) M1 catalyst. Firstly, the complex crystal structure of the M1 phases has been examined using quantum mechanics (QM), reactive force field (ReaxFF), and machine learning (ML) approaches. Secondly, we discussed the ODH mechanism on the M1 phase based on the QM simulations including the finite cluster model and the periodic slab model. Finally, we proposed a catalyst design approach to improve the selectivity of the M1 phase based upon the ODH reaction mechanism. We also briefly discuss the concept of the CE (“Concurrent Engineering”, introduced by the European Space Agency). The development of the CE concepts may be applied to the M1 catalytic systems in the future allowing businesses to be agile and react fast to the changing production conditions, thereby making them uniquely competitive in the ODH of alkanes and other areas.

Parallel Alkane Dehydrogenation Routes on Brønsted Acid and Reaction-Derived Carbonaceous Active Sites in Zeolites

Alkane dehydrogenation rates on acidic zeolites measured in the presence of co-fed H2 during initial contact with reactants solely reflect protolytic reactions at Bronsted acid sites, while rates m...

Sulfate-Modified NiAl Mixed Oxides as Effective C–H Bond-Breaking Agents for the Sole Production of Ethylene from Ethane

The oxidative dehydrogenation (ODH) of alkanes with N2O or CO2 is an attractive pathway to produce alkenes and decrease environmental issues. However, the sole production of alkenes from the ODH pr...

Alkane dehydrogenation on defective BN quasi-molecular nanoflakes: DFT studies

Lower alkanes are feedstocks readily available but relatively inert. The conversion of low cost alkanes to industrially relevant alkenes is usually carried out on metal-based heterogeneous catalysts. Considering both the cost and the potential harmfulness of the metal involved in the dehydrogenation catalysts (typically, platinum or chromium), the study of metal-free processes represents an important challenge for the industrial chemistry in order to address more sustainable protocols and different routes either to activate or transform alkanes. Framed in this context, it was investigated, using a density functional theory approach, the potential dehydrogenation activity of defective and partially hydrogenated boron nitride quasi-molecular nanoflakes, on ethane, chloroethane and phenylethane. Concerted and not concerted reactions were considered, resulting the former always favored with respect to the latter and being the mechanisms and the corresponding energy characterizing the different substrates, in any case, quite similar. Along the dehydrogenation, given a certain hydrocarbon adsorption constellation, the defective nitrogen sites were generally more active than the boron ones, being the energy barriers, in any case, smaller or at least comparable with those already observed for the metal catalyzed dehydrogenation processes. After the dehydrogenation processes, the hydrogenated boron nitride quasi-molecular nanoflakes resulted highly stabilized, suggesting that specific strategies are needed to employ these materials as catalysts.

Boosting the Performance of Alkanes’ Dehydrogenation Catalysts in the Industrial Scale by Altering the Water Injection Strategy

Water addition plays a pivotal role in prolonging the catalytic dehydrogenation reactions and normally starts at the beginning of the dehydrogenation process. A delayed water injection strategy is proposed in this study to improve the performance of bimetallic Pt-Sn/Al2O3 catalyst utilized for long-chain alkanes (nC10–C13) dehydrogenation in the industrial scale. The dehydrogenation reactions took place at a pressure of 0.11–0.13 MPa and temperature varied between 470 and 490 °C. Postponing the water supply until the middle of run leads to longer operating life for the catalyst and consequently reduces the production costs significantly. In addition, it promotes the quality of the final product by decreasing the undesired by-products and results in higher production capacities (by 1.5 %) in the industrial scale. Characterization of the deactivated dehydrogenation catalysts using different methods allows the understanding of the boosted performance of the catalyst arising from postponing the water injection process. Moreover, the proposed strategy reduces the waste production by decreasing the ratio of loaded catalyst to the desired product (by 23 %) and thus alleviates the negative environmental impact of the process. Furthermore, it results in lower energy consumption and promotes the mitigation of CO2 gas emissions by 3 % which can be effective in tackling environmental challenges in the large scale.

Dehydrogenation of Primary Alkyl Azides to Nitriles Catalyzed by Pincer Iridium/Ruthenium Complexes

AbstractPincer metal complexes exhibit superior catalytic activity in the dehydrogenation of plain alkanes, but find limited application in the dehydrogenation of functionalized organic molecules. Starting from easily accessible primary alkyl azides, here we report an efficient dehydrogenation of azides to nitriles using pincer iridium or ruthenium complexes as the catalysts. This method offers a route to cyanide‐free preparation of nitriles without carbon chain elongation and without the use of strong oxidants. Both benzyl and linear aliphatic azides can be dehydrogenated with tert‐butylethylene as the hydrogen acceptor to afford nitriles in moderate to high yields. Various functional groups can be tolerated, and the H−C−C−H bond dehydrogenation does not occur for linear alkyl azide substrates. Furthermore, the pincer Ir catalytic system was found to catalyze the direct azide dehydrogenation without the use of a sacrificial hydrogen acceptor.

N-Bridged Pincer Iridium Complexes for Highly Efficient Alkane Dehydrogenation and the Relevant Linker Effects

A series of iridium complexes (RPOCR′NP)–HCl (4–HCl) and (RPSCR′NP)Ir–HCl (5–HCl) (R = substituent on P; R′ = substituent on N) supported by N-linked pincer ligands, with the other linker being O- ...

NCP‐Type Pincer Iridium Complexes Catalyzed Transfer‐Dehydrogenation of Alkanes and Heterocycles†

Summary of main observation and conclusionA series of NCP‐type pincer iridium complexes, (RNCCP)IrHCl (2a—2c) and (BQ‐NCOP)IrHCl 3, have been studied for catalytic transfer alkane dehydrogenation. Complex 3 containing a rigid benzoquinoline backbone exhibits high activity and robustness in dehydrogenation of alkanes to form alkenes. Even more importantly, this catalyst system was also highly effective in the dehydrogenation of a wide range of heterocycles to furnish heteroarenes.

Single Vanadium Atoms Anchored on Graphitic Carbon Nitride as a High-Performance Catalyst for Non-oxidative Propane Dehydrogenation

In comparison with oil-based cracking technologies, the on-purpose dehydrogenation of propane (PDH) is a more eco-friendly and profitable approach to produce propylene. However, the prevalent industrial PDH catalyst, Pt-Sn, suffers from not only the high costs of Pt, but also fast deactivation triggered by sintering of Pt species. Thus, the development of more cost-efficient PDH catalysts with satisfactory stability and propylene selectivity has been a major focus of interests in the community of materials science. By means of density functional theory (DFT) calculations, the present work reveals that single vanadium (V) atom anchored on graphitic carbon nitride (V1/g-C3N4) may serve as a promising single-atom-catalyst for non-oxidative PDH with industrially practical activity, selectivity and thermal stability. The high activity of V1/g-C3N4 for PDH is attributed to the low-coordinated 3d orbitals of single V atoms, while the propylene selectivity is originated from the inhibition of di-σ binding mode of propylene on the single V atoms. This work provides a guideline to design and screen out promising single-atom catalysts for selective dehydrogenation of alkanes.

Cover Picture: Radical Chemistry and Reaction Mechanisms of Propane Oxidative Dehydrogenation over Hexagonal Boron Nitride Catalysts (Angew. Chem. Int. Ed. 21/2020)

Hexagonal boron nitride is an emerging catalyst for the oxidative dehydrogenation (ODH) of alkanes to produce olefins with high selectivity and activity. In their Communication on page 8042, V. Fung, W. Huang, Z. Wu et al. report the first direct experimental evidence for gas-phase methyl radicals (CH3.) in propane ODH over boron-based catalysts. The presence of gas-phase radicals is shown to be partially responsible for the generation of cracking products (C2 and C1) in propane ODH. Hexagonal boron nitride is an emerging catalyst for the oxidative dehydrogenation (ODH) of alkanes to produce olefins with high selectivity and activity. In their Communication on page 8042, V. Fung, W. Huang, Z. Wu et al. report the first direct experimental evidence for gas-phase methyl radicals (CH3.) in propane ODH over boron-based catalysts. The presence of gas-phase radicals is shown to be partially responsible for the generation of cracking products (C2 and C1) in propane ODH. Periodate Asymmetric Hydrogenation Double Perovskites Electrochemistry

Oxidative Dehydrogenation of Propane over Vanadium-Containing Faujasite Zeolite.

Oxidative dehydrogenation (ODH) of light alkanes to olefins—in particular, using vanadium-based catalysts—is a promising alternative to the dehydrogenation process. Here, we investigate how the activity of the vanadium phase in ODH is related to its dispersion in porous matrices. An attempt was made to synthesize catalysts in which vanadium was deposited on a microporous faujasite zeolite (FAU) with the hierarchical (desilicated) FAU as supports. These yielded different catalysts with varying amounts and types of vanadium phase and the porosity of the support. The phase composition of the catalysts was confirmed by X-ray diffraction (XRD); low temperature nitrogen sorption experiments resulted in their surface area and pore volumes, and reducibility was measured with a temperature-programmed reduction with a hydrogen (H2-TPR) method. The character of vanadium was studied by UV-VIS spectroscopy. The obtained samples were subjected to catalytic tests in the oxidative dehydrogenation of propane in a fixed-bed gas flow reactor with a gas chromatograph to detect subtract and reaction products at a temperature range from 400–500 °C, with varying contact times. The sample containing 6 wt% of vanadium deposited on the desilicated FAU appeared the most active. The activity was ascribed to the presence of the dispersed vanadium ions in the tetragonal coordination environment and support mesoporosity.

Active, Selective, and Durable Catalyst for Alkane Dehydrogenation Based on a Well-Designed Trimetallic Alloy

Catalyst design based on a pseudo-binary alloy concept was applied to develop a highly efficient catalytic system for alkane dehydrogenation. A series of Pt-based alloy catalysts supported on silic...

Progress in the oxidative dehydrogenation of light alkanes to light olefins on metal-free catalysts

Light alkenes are the key building blocks in chemical industry. Dehydrogenation of light alkanes to light olefins offers an important route for the value-added utilization of alkanes and the diversification in olefin supplies. Featured with the free coking and no thermodynamic restriction, oxidative dehydrogenation of alkanes to olefins has attracted much attention. The early reported metal oxide catalysts usually have good activities, but tend to deeply oxidize olefins to CO2, leading to poor yield of olefin products. Later on, metal-free catalysts start to catch the eye. As a new estabilished catalytic system, metal-free boron-based catalysts show distinctive reaction characteristics of the high selectivity of olefins and the inhibition of deep oxidation reactions, as compared to metal-based catalysts. Hexagonal boron nitride ( h -BN) was first proved to be a highly active catalyst in the oxidative dehydrogenation reaction. Afterwards, some borides (e.g., SiB6, CB4) and supported boron catalysts have also been reported. The boron-based catalysts exhibit high activities and selevtivities to olefins with negligible formations of CO2, which provides a new sight in the selective cleavage of C–H bonds. In the combination of spectroscopic and kinetic analysis, the BO x species on the catalyst surface was determined as the active sites. The unique catalysis of boron-based catalysts updates the traditional perception on the alkane activation and has becoming a new hotspot worldwide. Besides, other metal-free catalysts, nanostructured carbon-based materials including carbon nanotubes, carbon nanofibers and nano-diamonds have also been shown a great potential in the dehydrogenation of light alkanes. The carbonyl/quinone groups are verified to be the active sites for dehydrogenation of light alkanes; the carboxyl, carboxylic anhydride and lactone groups could act as deep oxidative sites and cause the reduction of olefin selectivity. Moreover, doping of heteroatoms (B, P and N) into carbon matrix is effective for the improvement of olefin selectivity. This review timely highlights the recent developments of metal-free catalysts in the oxidative dehydrogenation of light alkanes, particulary focusing on the newly established boron-based catalytic system. At the end, we propose the perspective research directions of the dehydrogenation of light alkanes.

Oxidative dehydrogenation of ethane using porous hexagonal boron nitride microtubes

Hexagonal boron nitride (h-BN) has recently aroused continuous interest in the oxidative dehydrogenation (ODH) of light alkanes. Here, we synthesized boron nitride microtubes (BNMTs) using a facile solid-phase reaction method, which possess a diameter distribution from 200 nm to 1 μm and the length can reach dozens of microns. In the ODH of ethane reaction, the conversion of ethane can reach 45% at an ethylene selectivity of 72% on the porous BNMTs at 600 °C. The novel BNMTs with high specific surface area and abundant BO and BOH species are favor of high performance in the ODH of ethane to ethylene.