Alkane Dehydrogenation Research Articles

Copper‐Catalyzed Simultaneous Dehydrogenation and Enantioselective Allylic Oxidation of Alkanes Using Chiral Heterogeneous Ligands to Produce Allylic Esters and Theoretical Investigation of the Mechanism

ABSTRACTA new asymmetric method for preparing chiral allylic esters from various unactivated alkanes through simultaneous dehydrogenation and enantioselective allylic oxidation in the presence of chiral heterogeneous oxazoline–based ligands is reported for the first time. For this purpose, chiral amino oxazoline ligands, synthesized from chiral amino alcohols and cyanogen bromide, were immobilized on modified MCM‐41 mesoporous silica. These chiral heterogeneous ligands were then characterized using Fourier‐transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and Brunauer–Emmett–Teller and Barrett–Joyner–Halenda techniques. Finally, copper complexes of these ligands were employed in the synthesis of chiral allylic esters, achieving the best result with a 90% yield and 77% enantiomeric excess. Evaluation of the recyclability of the chiral heterogeneous catalysts revealed that they can be reused three times without a noticeable reduction in the results. In addition, the mechanism of formation of the chiral allylic esters was investigated using a density functional theory method.

Enhanced Stability and Selectivity in Pt@MFI Catalysts for n-Butane Dehydrogenation: The Crucial Role of Sn Promoter

The dehydrogenation of n-butane to butenes is a crucial process for producing valuable petrochemical intermediates. This study explores the role of oxyphilic metal promoters (Sn, Zn, and Ga) in enhancing the performance and stability of Pt@MFI catalysts for n-butane dehydrogenation. The presence of Sn in the catalyst inhibits the agglomeration of Pt clusters, maintaining their subnanometric particle size. PtSn@MFI exhibits superior stability and selectivity for butenes while suppressing cracking reactions, with selectivity for C1–C3 products as low as 2.1% at 550 °C compared to over 30.5% for Pt@MFI. Using a combination of high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Raman spectroscopy, we examined the structural and electronic properties of the catalysts. Our findings reveal that Zn tends to consume hydroxyl groups and substitute framework sites, and Ga induces more defective sites in the zeolite structure. In contrast, the interaction between SnOx and the zeolite framework does not depend on reactions with hydroxyl groups. The incorporation of Sn significantly prevents Pt particle agglomeration, maintaining smaller Pt particle sizes and reducing coke formation compared to Zn and Ga promoters. Theoretical calculations showed that Sn increases the positive charge on Pt clusters, enhancing their interaction with the zeolite framework and reducing sintering, albeit with a slight increase in the energy barrier for C-H activation. These results underscore the dual benefits of Sn as a promoter, offering enhanced structural stability and reduced coke formation, thus paving the way for the rational design of more effective and durable catalysts for alkane dehydrogenation and other high-value chemical processes.

Selective Catalytic Combustion of Hydrogen under Aerobic Conditions on Na2WO4/SiO2

AbstractNa2WO4/SiO2, a material known to catalyze alkane selective oxidation including the oxidative coupling of methane (OCM), is demonstrated to catalyze selective hydrogen combustion (SHC) with >97 % selectivity in mixtures with several hydrocarbons (CH4, C2H6, C2H4, C3H6, C6H6) in the presence of gas‐phase dioxygen at 883–983 K. Hydrogen combustion rates exhibit a near‐first‐order dependence on H2 partial pressure and are zero‐order in H2O and O2 partial pressures. Mechanistic studies at 923 K using isotopically‐labeled reagents demonstrate the kinetic relevance of H−H dissociation and absence of O‐atom recombination. In situ X‐ray diffraction (XRD) and W LIII‐edge X‐ray absorption spectroscopy (XAS) studies demonstrate, respectively, a loss of Na2WO4 crystallinity and lack of second‐shell coordination with respect to W6+ cations below 923 K; benchmark experiments show that alkali cations must be present for the material to be selective for hydrogen combustion, but that materials containing Na alone have much lower combustion rates (per gram Na) than those containing Na and W. These data suggest a synergy between Na and W in a disordered phase at temperatures below the bulk melting point of Na2WO4 (971 K) during SHC catalysis. The Na2WO4/SiO2 SHC catalyst maintains stable combustion rates at temperatures ca. 100 K higher than redox‐active SHC catalysts and could potentially enable enhanced olefin yields in tandem operation of reactors combining alkane dehydrogenation with SHC processes.

Facile and Environmentally Friendly Synthesis of Ga2O3/MFI Catalysts for Propane Dehydrogenation.

A GaOx-based catalyst is recognized as a promising catalyst for dehydrogenation of light alkanes. Conventionally, impregnation and calcination are necessary processes for the loading of GaOx. However, the incomplete impregnation of gallium salt solution would generate wastewater, and the calcination for the dissociation of gallium salt would release harmful gases, such as SOx, NOx, and HCl. Meanwhile, the high temperature results in an excessive energy cost and undesired GaOx particle aggregation. Here, we report a facile and environmentally friendly method for the synthesis of GaOx-based catalysts. The gallium salt solution was replaced directly with liquid gallium (LG). Through a simple physical mixing method at room temperature, uniform GaOx nanoparticles with diameters of around 3.5 nm were loaded onto the surface of silicalite-1 (S-1). With the optimal GaOx/MFI catalyst, the propane conversion and propylene selectivity reached 22.9 and 90.1%, respectively, in the propane dehydrogenation reaction. The work offers a clean and economical strategy utilizing liquid metal (LM) as an impregnation solution for the preparation of GaOx-based catalysts.

Ab initio molecular dynamics simulation reveals the influence of entropy effect on Co@BEA zeolite-catalyzed dehydrogenation of ethane

The C–H bond activation in alkane dehydrogenation reactions is a key step in determining the reaction rate. To understand the impact of entropy, we performed ab initio static and molecular dynamics free energy simulations of ethane dehydrogenation over Co@BEA zeolite at different temperatures. AIMD simulations showed that a sharp decrease in free energy barrier as temperature increased. Our analysis of the temperature dependence of activation free energies uncovered an unusual entropic effect accompanying the reaction. The unique spatial structures around the Co active site at different temperatures influenced both the extent of charge transfer in the transition state and the arrangement of 3d orbital energy levels. We provided explanations consistent with the principles of thermodynamics and statistical physics. The insights gained at the atomic level have offered a fresh interpretation of the intricate long-range interplay between local chemical reactions and extensive chemical environments.

Cr-MIL-101 derived nano Cr2O3 for highly efficient dehydrogenation of n-hexane

Nano Cr2O3 (n-Cr2O3) was prepared by the thermolysis of the mesoporous Cr-MIL-101, and its catalytic performance for n-hexane dehydrogenation was investigated and compared with Cr2O3 obtained by traditional method. It is found that dehydrogenation of n-hexane on n-Cr2O3 catalyst can produce n-hexenes and benzene efficiently, and the catalytic performance is related to the calcination temperature. The optimal n-hexane conversion can be obtained on n-Cr2O3 calcinated under 600 °C, is 40.6%, and the selectivities to n-hexenes and benzene are 20.1% and 69.3%, respectively. The conversion of n-hexane for n-Cr2O3 catalyst is decreased with calcination temperature increase, while the catalyst stability in dehydrogenation reaction is enhanced. n-Hexane conversion of p-Cr2O3-1 (obtained by precipitation method) and p-Cr2O3-2 (calcinating Cr(NO3)·9H2O directly) catalysts are very low (<7.5%), and their specific activity for n-hexane dehydrogenation are 1.5 and 1.7 g/(m2·h) respectively, lower than that of n-Cr2O3-600 (2.0 g/(m2·h)). The results of BET, XRD, TEM and FT-IR reveal that n-Cr2O3 is the nanoparticles with large specific surface area that more dehydrogenation active sites are exposed, while p-Cr2O3 is the large particles with extremely low surface area that few dehydrogenation active sites are presented. By contrast, industrial Cr2O3/Al2O3 catalyst possesses the highest specific activity of 2.4 g/(m2·h) due to the dispersion effect of Al2O3. Therefore, highly catalytic activity of n-Cr2O3 for n-hexane dehydrogenation is attributed to the unique properties of small particle, large specific surface area and more exposed active sites. This work not only explains the high dehydrogenation activity of nano-Cr2O3 derived by Cr-MIL-101, but also provides guidance for the precise design and synthesis of high-performance CrOx-based catalyst for the dehydrogenation of alkanes.

Theoretical screening of single-atom catalysts (SACs) on Mo2TiC2O2 MXene for methane activation

Producing value-added chemicals and fuels from methane (CH4) under mild conditions efficiently utilizes this cheap and abundant feedstock, promoting economic growth, energy security, and environmental sustainability. However, the first CH bond activation is a significant challenge and requires high energy. Efficient catalysts have been sought for utilizing CH4 at low temperatures including emerging single-atom catalysts (SACs). In this work, we screened fourteen transition metals (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Pt) doped at a single oxygen vacancy in Mo2TiC2O2 (TMSA-Mo2TiC2O2 SACs) for methane activation using density functional theory (DFT) calculations. Our results reveal that methane adsorption is thermodynamically stable on all simulated TMSA-Mo2TiC2O2 SACs, with the adsorption energies (Eads) ranging from −0.92 to −0.40 eV. For the CH activation process, Ru-SAC exhibits the lowest activation barrier (Ea) of 0.22 eV. In summary, Ru-, Rh-, Co-, V-, Cr-, Ti-, and Pt-SACs demonstrate promising catalytic properties for methane activation, with Ea values below 1.0 eV and an exothermic nature. Our findings pave the way for the design and development of novel single-atom catalysts in MXene materials, applicable not only for methane activation but also for other alkane dehydrogenation processes.

Material Engineering Solutions toward Selective Redox Catalysts for Chemical-Looping-Based Olefin Production Schemes: A Review.

Chemical looping (CL) has emerged as a promising approach in the oxidative dehydrogenation (ODH) of light alkanes, offering an opportunity for significant reductions in emissions and energy consumption in the ethylene and propylene production industry. While high olefin yields are achievable via CL, the material requirements (e.g., electronic and geometric structures) that prevent the total conversion of alkanes to CO x are not clearly understood. This review aims to give a concise understanding of the nucleophilic oxygen species involved in the selective reaction pathways for olefin production as well as of the electrophilic oxygen species that promote an overoxidation to CO x products. It further introduces advanced characterization techniques such as X-ray photoelectron spectroscopy, Raman spectroscopy, electron paramagnetic resonance spectroscopy, and resonant inelastic X-ray scattering, which have been employed successfully in identifying such reactive oxygen species. To mitigate CO x formation and enhance olefin selectivity, material engineering solutions are discussed. Common techniques include doping of the bulk or surface and the deposition of functional coatings. In the context of energy consumption and CO2 intensity, techno-economic assessments of CL-ODH systems have predicted energy savings of up to 80% compared to established olefin production processes such as steam cracking or dehydrogenation. Finally, although their practical application has been limited to date, the potential advantages of the use of fluidized bed reactors in CL-ODH are presented.

Investigation of the CO2 Activation and Regeneration of Reduced VOx/CeO2 Catalysts Using Multiple In Situ Spectroscopies

AbstractCeria‐supported vanadium oxide (VOx/CeO2) is an important catalyst for various oxidation reactions. Recently, vanadia has emerged again as a less toxic alternative to CrOx‐based catalysts for the CO2‐assisted oxidative dehydrogenation (ODH) of alkanes. To establish a mechanistic understanding of catalyst regeneration during CO2 exposure, often described as the rate‐limiting step of these reactions, we investigated the regeneration of VOx/CeO2 catalysts with different vanadia loadings using multiple in situ spectroscopies, that is, multi‐wavelength Raman, UV‐Vis, IR and X‐ray photoelectron spectroscopy. Time‐dependent analysis reveals that ceria is only partially regenerated in the bulk but fully regenerated in the subsurface. At the surface, stable carbonates form at vacancies, which are able to regenerate the lattice and deactivate ceria surface oxygen. The VOx/CeO2 samples show a loading‐dependent behavior, with low‐loaded samples regenerating vanadia only partially, due to the high concentration of monomers, while at higher loadings, vanadia can be almost fully regenerated due to the higher nuclearities being thermodynamically more stable. Ceria is regenerated faster than vanadia, indicating that vanadia regenerates by oxygen spill‐over from the ceria lattice. Our results provide important mechanistic insight into CO2 activation over supported vanadia catalysts, which is of great relevance for CO2‐assisted ODH reactions.

Selective Catalytic Combustion of Hydrogen under Aerobic Conditions on Na2WO4/SiO2.

Na2WO4/SiO2, a material known to catalyze oxidative coupling of methane, is demonstrated to catalyze selective hydrogen combustion (SHC) with >97% selectivity in mixtures with several hydrocarbons (CH4, C2H-6, C2H4, C3H6, C6H6) in the presence of gas-phase dioxygen at 883-983 K. Hydrogen combustion rates exhibit a near-first-order dependence on H2 partial pressure and are zero-order in H2O and O2 partial pressures. Mechanistic studiesusing isotopically-labeled reagents demonstrate the kinetic relevance of H-H dissociation and absence of O-atom recombination. In situ X-ray diffraction and W LIII-edge X-ray absorption spectroscopystudies demonstrate, respectively, a loss of Na2WO4 crystallinity and lack of second-shell coordination with respect to W6+ cations below 923 K; benchmark experiments show that alkali cations must be present for the material to be selective for hydrogen combustion, but that materials containing Na alone have much lower combustion rates (per gram Na) than those containing Na and W. These data suggest a synergy between Na and W in a disordered phaseduring SHC catalysis. The Na2WO4/SiO2 SHC catalyst maintains stable combustion rates at temperatures ca. 100 K higher than redox-active SHC catalysts and could potentially enable enhanced olefin yields in tandem operation of reactors combining alkane dehydrogenation with SHC processes.

Breaking the stability limit of zeolite-based alkane dehydrogenation catalysts

Metal catalysts confined inside zeolite micropores or crystals are widely applied in the chemical industry because of their distinctive catalytic functions, especially with regard to the conversion of small and stable alkane molecules [1,2]. Silicalite-1 (S-1), a pure silica zeolite with an MFI topology, has a robust framework capable of withstanding harsh thermal and chemical conditions. Recently, S-1-based catalysts have demonstrated significant advantages in the construction and stabilization of various active metal centers and have attracted considerable attention for their potential in alkane dehydrogenation reactions. The absence of acidic sites prevents various acid-catalyzed side reactions, rendering S-1 a promising candidate for high-temperature reactions such as non-oxidative propane dehydrogenation (PDH). Sun et al. revealed that encapsulating subnanometer bimetallic PtZn clusters in S-1 resulted in a high propylene selectivity of 99%, with no catalyst deactivation even after 200h in the PDH reaction [3]. However, sustaining high stability at high conversion rates is still challenging for PDH reactions, and commercial processes are still based on Pt- and Cr-based catalysts, which need frequent regeneration.

Highly Stable Subnanometric PtIn Clusters for the Selective Dehydrogenation of Alkanes.

Subnanometric PtIn clusters have been synthesized within pure silica MFI zeolites by post-synthetic incorporation of In to Pt@K-MFI. The optimized PtIn@K-MFI catalyst outcompetes state-of-the-art PtSn formulations in ethane and propane dehydrogenations, avoiding the need of large excess of Pt promoters and harsh reductive conditions.

STUDYING THE INFLUENCE OF ALKALINE TREATMENT AND MODIFICATION OF ZEOLITE ON ITS PHYSICAL-CHEMICAL AND CATALYTIC PROPERTIES IN THE PROCESS OF PROPANE CONVERSION TO OLEFIN HYDROCARBONS

In this work, the effect of alkaline treatment of ZSM-5 zeolite with a modulus of 100 on its physicochemical properties and activity in the process of converting propane into olefin hydrocarbons was investigated. The growing demand for lower olefins is driving the search for new ways to improve existing technologies and develop new, more efficient catalysts. Catalytic dehydrogenation of light alkanes is an alternative to the petrochemical method for producing lower olefins from cheap and available gas and oil and gas feedstocks. At the same time, dehydrogenation reactions of light alkanes have a number of features and limitations that determine the range of possible catalysts. Zeolites are a class of supports that, due to their large surface area, nanometer-sized pores, and good thermal stability, can be used to prepare catalysts for the dehydrogenation of C2−C4 alkanes. An important feature of crystalline high-silica zeolites is the ability to change their acidic properties under the influence of various pre-treatments, which opens up great opportunities for their regulation and, accordingly, the selection of the most effective catalyst for a particular chemical process. It has been shown that alkaline treatment of zeolite leads to the formation of an additional amount of mesopores, which, in turn, affects its catalytic properties in the process of converting propane into olefinic hydrocarbons. The dependence of the activity and selectivity of the zeolite catalyst on the concentration of the alkali solution used for its treatment has been established. It was found that treatment of the zeolite catalyst with a 1.0 M NaOH solution leads to an increase in its selectivity with respect to the formation of C2–C4 olefins from propane, which at a process temperature of 650 °C reaches 32.0% with a propane conversion of 81%. It has been shown that additional promotion of desilicated zeolite with magnesium or manganese increases its activity with respect to the formation of olefinic hydrocarbons from propane. For citation: Vosmerikov A.A., Vosmerikova L.N., Vosmerikov A.V. Studying the influence of alkaline treatment and modification of zeolite on its physical-chemical and catalytic properties in the process of propane conversion to olefin hydrocarbons. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 8. P. 50-58. DOI: 10.6060/ivkkt.20246708.11t.

Carbon-Boosted and Nitrogen-Stabilized Isolated Single-Atom Sites for Direct Dehydrogenation of Lower Alkanes.

Lower olefins are widely used in the chemical industry as basic carbon-based feedstocks. Here, we report the catalytic system featuring isolated single-atom sites of iridium (Ir1) that can function within the entire temperature range of 300-600 °C and transform alkanes with conversions close to thermodynamics-dictated levels. The high turnover frequency values of the Ir1 system are comparable to those of homogeneous catalytic reactions. Experimental data and theoretical calculations both indicate that Ir1 is the primary catalytic site, while the coordinating C and N atoms help to enhance the activity and stability, respectively; all three kinds of elements cooperatively contribute to the high performance of this novel active site. We have further immobilized this catalyst on particulate Al2O3, and we found that the resulting composite system under mimicked industrial conditions could still give high catalytic performances; in addition, we have also developed and established a new scheme of periodical in situ regeneration specifically for this composite particulate catalyst.

An Iminophosphinite Pincer Iridium Complex: Synthesis and Catalytic Tool for Alkane Transfer Dehydrogenations

AbstractA [(POCN)Ir(H)(OAc)] complex bearing an iminophosphinite pincer ligand was synthesized. The complex showed catalytic transfer dehydrogenation of various linear and cyclic alkanes with reasonable conversions and a maximum TON of 400 for n‐octane. A catalytic isomerization of 1‐octene to yield internal octenes was also possible. It is notable that the catalyst could perform catalytic transfer dehydrogenation even at a temperature of 100 °C with a TON of 100.

Deactivation of an Fe-based catalyst in the dehydrogenation of light alkanes under H2S co-feeding: A case study

The effectiveness of a Ru-Fe/SiO2 catalyst, which exhibits excellent propane dehydrogenation with H2S co-feeding, was verified for the dehydrogenation of various lower alkanes. When the dehydrogenation characteristics of C2–C4 alkanes were evaluated under H2S co-feeding, the Ru-Fe/SiO2 catalyst exhibited a high dehydrogenation activity in all cases. However, a significant degradation tendency of the catalyst was observed when lighter alkanes with smaller carbon numbers were used as the feedstock. The deposition of coke (carbon) and solid sulfur and the reduction of Fe species were identified as the main factors responsible for catalyst degradation. To further evaluate the factors affecting catalyst degradation, the effect of co-feeding H2 with the gas feedstock on the catalyst performance was investigated. The reaction stability improved significantly with the co-feeding of H2 during ethane and propane dehydrogenation reactions. This outcome is attributed to the smooth reduction and removal of the carbon accumulated on the catalyst surface, which is the main cause of catalyst degradation.

Visible‐Light‐Driven Formyl Group Migration Triggered Remote Desaturation

AbstractDehydrogenation of unactivated alkanes to form versatile alkenes is an important but challenging task in synthetic chemistry. Enabled by a radical‐mediated formyl group migration, a novel visible light‐induced remote desaturation of aldehydes is developed, delivering a panel of trifluoromethylated δ,ϵ‐ or γ,δ‐unsaturated aldehydes in moderate to excellent yields with good functional group tolerance at room temperature. Mechanistic studies indicate a reaction pathway comprising the cascade trifluoromethylation of C−C double bonds, intramolecular addition to aldehydes, β‐fragmentation of alkoxy radicals, single electron transfer oxidation, and deprotonation. It provides a good complementary approach to the existing desaturation protocols.

Unraveling the function of monolayer shell structure over Pt-based alloy catalysts in tuning ethane dehydrogenation reactivity and coking resistance

Ethane direct dehydrogenation (EDH) operated at high temperature easily leads to coke formation. The new core–shell catalysts with monolayer shell exhibited better catalytic performance, and the function of monolayer shell structure is of great importance. This work fully investigated catalytic performance of EDH over six types of core–shell Pt3M@Pt and Pt@Pt3M (M = Fe, Co, and Ni) catalysts with Pt3M and Pt monolayer shell under the experimental conditions. Here, density functional theory (DFT) calculations with kinetic Monte Carlo (kMC) simulations were employed. The results show that the metal M over Pt3M@Pt surface decreases coordination number of Pt-Pt and restricts deep dehydrogenation reactions. The Pt3M@Pt catalysts with d-band center close to Fermi level exhibit higher C2H4(g) formation activity than Pt@Pt3M catalysts at 873.15 K. H2(g) co-feeding significantly decreases the coverage of coking C*+CC* species. The screened Pt3Ni@Pt catalyst presents the highest C2H4(g) formation activity and 100 % selectivity at the H2(g) partial pressure of 0.1 bar and reaction temperature 873.15 K, which is superior to previously reported Pt, Pt3Sn, 1Pt3Sn@4Pt, Pd1-NDG, Pt2/Al2O3 and Rh/ZrO2 catalysts. H* adsorption energy is proposed as a descriptor to quickly evaluate C2H4(g) formation activity. This work provides a useful strategy for designing alkane dehydrogenation catalysts by tuning monolayer shell structure and coordination environment of active site.

Integrated Carbon Dioxide Capture and Utilization for the Production of CH4, Syngas and Olefins over Dual‐Function Materials

AbstractThe massive emission of carbon dioxide produces the greenhouse effect and poses a threat to the survival of modern civilization. The search for new carbon management strategies has been at the forefront of scientific research over the past few decades. Integrated carbon dioxide capture and utilization (ICCU), which aims to capture CO2 and convert it in situ into high value‐added products or fuels, is considered to be more attractive and innovative than alternative strategies. This paper introduces the adsorption capacity and characteristics of solid sorbents at different operating temperatures. On this basis, the recent research on ICCU technology combined with methanation, reverse water−gas shift reaction, dry reforming of alkanes and dehydrogenation of alkanes over novel dual‐function materials is presented, and the development direction and future prospects of ICCU are discussed.

Novel Alkane Dehydrogenation Routes via Tailored Catalysts

AbstractAlkane dehydrogenation to alkene represents a promising alternative route for conventional petroleum cracking processes heavily reliant on fossil resources. This Concept outlines the latest advancements of novel alkane dehydrogenation routes that offer potential solutions to intrinsic problems existing in routine direct dehydrogenation or oxidative dehydrogenation reactions, including CO2 assisted alkane dehydrogenation, chemical looping alkane oxidative dehydrogenation, dual‐path dehydrogenation and auto‐accelerated multiple alkane dehydrogenation route. These novel reaction routes exhibit unique advantages in enhancing the activity, selectivity and stability of the alkane dehydrogenation reaction system. The rational design of novel catalysts and proper choice of the reaction condition that well‐fitted these reaction routes is the key for achieving highly efficient and stable alkane dehydrogenation process. These present examples in this manuscript also highlight the importance of fundamental in‐depth understandings on the mechanism and structure‐function relations, which is the foundation for developing novel alkane dehydrogenation routes for practical applications.