CO_(2)-assisted oxidation dehydrogenation of light alkanes over metal-based heterogeneous catalysts

Light olefins are important platform feedstocks in the petrochemical industry,and the ongoing global economic development has driven sustained growth in demand for these compounds.The dehydrogenation of alkanes,derived from shale gas,serves as an alternative olefins production route.Concurrently,the target of realizing carbon neutrality promotes the comprehensive utilization of greenhouse gas.The integrated process of light alkanes dehydrogenation and carbon dioxide reduction(CO_(2)-ODH)can produce light olefins and realize resource utilization of CO_(2),which has gained wide popularity.With the introduction of CO_(2),coke deposition and metal reduction encountered in alkanes dehydrogenation reactions can be effectively suppressed.CO_(2)-assisted alkanes dehydrogenation can also reduce the risk of potential explosion hazard associated with O_(2)-oxidative dehydrogenation reactions.Recent investigations into various metal-based catalysts including mono-and bi-metallic alloys and oxides have displayed promising performances due to their unique properties.This paper provides the comprehensive review and critical analysis of advancements in the CO_(2)-assisted oxidative dehydrogenation of light alkanes(C2-C4)on metal-based catalysts developed in recent years.Moreover,it offers a comparative summary of the structural properties,catalytic activities,and reaction mechanisms over various active sites,providing valuable insights for the future design of dehydrogenation catalysts.

Electrospinning synthesis of porous boron-doped silica nanofibers for oxidative dehydrogenation of light alkanes

The discovery of the high activity and selectivity of boron-based catalysts for oxidative dehydrogenation(ODH)of alkanes to olefins has attracted significant attention in the exploration of a new method for the synthesis of highly active and selective catalysts.Herein,we describe the synthesis of porous boron-doped silica nanofibers(PBSNs)100-150 nm in diameter by electrospinning and the study of their catalytic performance.The electrospinning synthesis of the catalyst ensures the uniform dispersion and stability of the boron species on the open silica fiber framework.The one-dimensional nanofibers with open pore structures not only prevented diffusion limitation but also guaranteed high catalytic activity at high weight hourly space velocity(WHSV)in the ODH of alkanes.Compared to other supported boron oxide catalysts,PBSN catalysts showed higher olefin selectivity and stability.The presence of Si-OH groups in silica-supported boron catalysts may cause low propylene selectivity during the ODH of propane.When the ODH conversion of ethane reached 44.3%,the selectivity and productivity of ethylene were 84%and 44.2%g_(cat)^(-1)s^(-1),respectively.In the case of propane ODH,the conversion,selectivity of olefins,and productivity of propylene are 19.2%,90%,and 76.6 jimol g_(cat)^(-1)s^(-1),respectively.No significant variations in the conversion and product selectivity occurred during 20 h of operation at a high WHSV of 84.6 h^(-1).Transient analysis and kinetic experiments indicated that the activation of O2 was influenced by alkanes during the ODH reaction.

A viewpoint on catalytic origin of boron nitride in oxidative dehydrogenation of light alkanes

Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics,but encounters difficulties in selectivity control for alkenes because of over-oxidation reactions that produce a substantial amount of undesired carbon oxides.Recent progress has revealed that boron nitride is a highly promising catalyst in the oxidative dehydrogenation of light alkanes because of its superior selectivity for and high productivity of light alkenes,negligible formation of CO2,and remarkable catalyst stability.From this viewpoint,recent works on boron nitride in the oxidative dehydrogenations of ethane,propane,butane,and ethylbenzene are reviewed,and the emphasis of this viewpoint is placed on discussing the catalytic origin of boron nitride in oxidative dehydrogenation reactions.After analyzing recent progress in the use of boron nitride for oxidative dehydrogenation reactions and finding much new evidence,we conclude that pure boron nitride is catalytically inert,and an activation period is required under the reaction conditions;this process is accompanied by an oxygen functionalization at the edge of boron nitride;the B-O species themselves have no catalytic activity in C-H cleavage,and the B-OH groups,with the assistance of molecular oxygen,play the key role in triggering the oxidative dehydrogenation of propane;the dissociative adsorption of molecular oxygen is involved in the reaction process;and a straightforward strategy for preparing an active boron nitride catalyst with hydroxyl groups at the edges can efficiently enhance the catalytic efficacy.A new redox reaction cycle based on the B-OH sites is also proposed.Furthermore,as this is a novel catalytic system,there is an urgent need to develop new methods to optimize the catalytic performances,clarify the catalytic function of boron species in the alkane ODH reactions,and disclose the reaction mechanism under realistic reaction conditions.

Synthesis of straight-chain C_(49)H_(100) alkane using a modular splicing strategy

Ultra-long n-alkanes are highly valuable in both scientific research and as major constituents of specialty high-melting-point waxes.Unlike conventional methods(e.g.,Fischer–Tropsch(FT),ethylene oligomerization,and polyethylene cracking)typically resulting in wide n-alkane distributions,the elaborate design strategy presented herein allows the direct synthesis of pure,long n-alkanes using a modular splicing method with acetone,furfural,and fatty acid anhydrides or acyl chlorides as bio-blocks.The herein approach is based on a simple four-step catalytic reaction scheme involving C–C chain elongation and C–O bond activation.The synthesized pure n-alkanes had a carbon chain length as high as C_(49)(total yield of 49%).The synthesis approach also allows to selectively prepare n-alkanes with even and odd carbon numbers ranging from C15 to C_(49).This process represents a great breakthrough in the synthesis of long-chain pure n-alkanes,surpassing the carbon number limitations reported in previous methodologies.

Synthesis of aligned carbon nanotube with straight-chained alkanes by nebulization method

Aligned carbon nanotubes(CNTs)were synthesized by nebulized spray pyrolysis of solutions of organometallics in carbon precursor solvents.Four types of straight-chained alkanes including n-pentane,n-hexane,n-heptane and n-octane were used as precursor solvents for synthesis of aligned CNTs.The results from scanning electron microscopy,transmission electron microscopy and Raman spectroscopy show that the CNTs obtained from them have different diameters and degrees of graphitization. It is found that the n-heptane is the most suitable for the growth of aligned CNTs with high quality and yield.The thermodynamic properties of precursory carbon sources such as boiling point and formation enthalpy are considered to play a decisive role in the synthesis of CNTs.It will be very helpful for the controllable preparation of aligned CNTs at relatively low cost.

A high propylene productivity over B2O3/SiO2@honeycomb cordierite catalyst for oxidative dehydrogenation of propane

Boron-based metal-free catalysts for oxidative dehydrogenation of propane(ODHP)have drawn great attention in both academia and industry due to their impressive activity and olefin selectivity.Herein,the SiO2 and B2O3 sequentially coated honeycomb cordierite catalyst is designed by a two-step wash-coat method with different B2O3 loadings(0.1%–10%)and calcination temperatures(600,700,800℃).SiO2 obtained by TEOS hydrolysis acts as a media layer to bridge the cordierite substrate and boron oxide via abundant Si\\OH groups.The welldeveloped straight channels of honeycomb cordierite make it possible to carry out the reactor under high gas hourly space velocity(GHSV)and the thin wash-coated B2O3 layer can effectively facilitate the pore diffusion on the catalyst.The prepared B2O3/SiO2@HC monolithic catalyst exhibits good catalytic performance at low boron oxide loading and achieves excellent propylene selectivity(86.0%),olefin selectivity(97.6%,propylene and ethylene)and negligible CO2(0.1%)at 16.9%propane conversion under high GHSV of 345,600 ml·(g B2O3)^-1·h^-1,leading to a high propylene space time yield of 15.7 g C3H6·(g B2O3)^-1·h^-1 by suppressing the overoxidation.The obtained results strongly indicate that the boron-based monolithic catalyst can be properly fabricated to warrant the high activity and high throughput with its high gas/surface ratio and straight channels.

Heterogeneous catalytic partial oxidation of lower alkanes(C_1–C_6) on mixed metal oxides

This review paper aims at analysing the state of the art for partial oxidation and oxidative dehydrogenation（ODH） reactions of lower alkanes C–Cinto olefins and oxygenated products（aldehydes, anhydrides,carboxylic acids） on metal oxide catalysts with cations of variable oxidation state, such as Mo and V in particular. Key parameters to be met by the catalysts, such as their redox properties, their structural aspects, active sites composed of ensembles of atoms isolated one from the others, mechanisms of reactions, are discussed. Main features of the different reactions of C–Calkanes and catalysts are analysed and their generalisation for determining more active and more selective catalysts is attempted. Prospective views for the future of the domain are proposed.

Pt confined in Sn-ECNU-46 zeolite for efficient alkane dehydrogenation

Highly dispersed and stable Pt-based catalysts play a crucial role in constructing efficient catalytic systems for alkane dehydrogenation.In this study,a novel bimetallic Pt-Sn catalyst confined in extra-large-pore ECNU-46 zeolite(denoted as Pt/Sn-ECNU-46)is prepared by post-treatment.The open-site framework Sn species((SiO)_(3)Sn-OH)serve as anchors to interact with Pt species,favoring the high dispersion of Pt.On the other hand,the framework Sn species act as the second metal to regulate the geometrical and electronic environment of Pt species,thus suppressing their accumulation.Pt/Sn-ECNU-46 achieves a good performance in propane dehy-drogenation(PDH)reaction with high initial propane conversion(46%)and propylene selectivity(>99%)as well as regeneration ability.In addition,Pt/Sn-ECNU-46 is also active in the dehydrogenation of n-hexane.This study explores the application of extra-large-pore zeolite as support in constructing metal-confined catalysts for alkane dehydrogenation.

Studies of the roles of Sn or Fe on γ-Al_2O_3-supported Pt catalysts by CO adsorption microcalorimetry and dehydrogenation reaction of C_4 alkanes

CO adsorption microcalorimetry was employed in the study of γ-Al-2O-3-supported Pt, Pt-Sn and Pt-Fe catalysts. The results indicated that the initial differential heat of CO adsorption of the Pt/γ-Al-2O-3 catalyst was 125 kJ/mol. As CO coverage increased, the differential heat of adsorption decreased. At higher coverages, the differential heat of adsorption decreased significantly. 60% of the differential heat of CO adsorption on the Pt/γ-Al-2O-3 catalyst was higher than 100 kJ/mol. No significant effect on the initial differential heat was found after adding Sn and Fe to the Pt/γ-Al-2O-3 catalyst. The amount of strong CO adsorption sites decreased, while the portion of CO adsorption sites with differential heat of 60110 kJ/mol increased after increasing the Sn or Fe content. This indicates that the surface adsorption energy was changed by adding Sn or Fe to Pt/γ-Al-2O-3. The distribution of differential heat of CO adsorption on the Pt-Sn（C）/γ-Al-2O-3 catalyst was broad and homogeneous. Comparison of the dehydrogenation performance of C-4 alkanes with the number of CO adsorption sites with differential heat of 60110 kJ/mol showed a good correlation. These results indicate that the surface Pt centers with differential heats of 60110 kJ/mol for CO adsorption possess superior activity for the dehydrogenation of alkanes.

Solid catalysts for the dehydrogenation of long-chain alkanes:lessons from the dehydrogenation of light alkanes and homogeneous molecular catalysis

Long-chain alkanes are abundant feedstocks supplied by natural resources and chemical industry. Specially, normal long-chain alkanes are primary products from Fischer-Tropsch synthesis(FTS) process, which is an important route for the utilization of coal in China. Facing a shift of energy nexus towards sustainable society, the conversion of long-chain alkanes derived from coal into value-added products(such as alkenes and oxygenates) is of great importance for securing China’s energy supply and the role transition of the commercial FTS plants from fuel makers to chemical suppliers. Among the potential transformation routes,the direct dehydrogenation of long-chain alkanes into alkenes is an attractive and practical route, due to the broad applications of long-chain alkenes(especially the linear α-olefins). In this review, we will summary the key insights obtained from the literature on the dehydrogenation of light alkanes based on supported metal catalysts and the dehydrogenation of alkanes with homogeneous molecular catalysts and then discuss how to translate these lessons into the development of efficient catalysts and processes for the dehydrogenation of long-chain alkanes into long-chain alkenes.

Dehydrogenation Based Asymmetric Epoxidation of Arylalkanes to Chiral Epoxides

We report herein a formal asymmetric epoxidation of arylalkanes enabled by a one-pot dual-catalysts system comprising a pincer Ir catalyst for alkane dehydrogenation-alkene isomerization(AD-ISO)and a chiral ketone catalyst for asymmetric alkene epoxidation.This protocol provides a catalytic method for the synthesis of aryl epoxides in useful yields with high regio-and stereoselectivity directly from readily available alkyl arenes.Stereospecific derivatizations of the epoxidation product allow access to various enantioenriched compounds.

Recent progress in Cr-based catalysts for oxidative dehydrogenation of light alkanes by employing CO_(2) as a soft oxidant

CO_(2) can be used as a soft oxidant for oxidative dehydrogenation of light alkanes(CO_(2)-ODH),which is beneficial to realize the reuse of CO_(2) and meet the demand for olefins.The core of this reaction is the catalyst.Cr-based catalysts have attracted much attention for their excellent catalytic performance in CO_(2)-ODH reactions due to their various oxidation states and local electronic structures.In this paper,the synthesis and modification methods of Cr-based catalysts for CO_(2)-ODH are reviewed.The structure-activity relationship and reaction mechanism are also summarized.Moreover,the reasons for the deactivation of Cr-based catalysts are analysed and the main challenges faced by Cr-based catalysts in the CO_(2)-ODH process,as well as the future development trend and prospect,are discussed.

制备方法对Pt-Sn-K-Mg/γ-Al_(2)O_(3)催化剂正十二烷脱氢性能的影响

以正十二烷脱氢反应为探针反应,采用顺序浸渍、乙醇共浸渍、盐酸共浸渍的方法制备了Pt-Sn-K-Mg/γ-Al_(2)O_(3)催化剂,并采用NH_(3)-TPD、CO脉冲吸附、H_(2)-TPR、准原位XPS等表征手段探究浸渍顺序和溶剂对催化剂构效关系的影响.结果表明,盐酸水溶液共浸渍的方法制备的催化剂表现出了最佳的初始活性和较好的稳定性.催化剂的弱酸性位点的增加有利于Pt的分散,从而提高催化性能.采用乙醇为溶剂的共浸渍方法更有利于PtSn间形成更强的相互作用生成更多的PtSn合金,这对初始活性不利,但对选择性影响较小.

Two-dimensional atomically thin Pt layers on MXenes: The role of electronic effects during catalytic dehydrogenation of ethane and propane

Atomically thin Pt nanolayers were synthesized on the surface of Mo2TiC2 MXenes and used for the catalytic dehydrogenation of ethane and propane into ethylene and propylene,two important chemicals for the petrochemical industry.As compared with Pt nanoparticles,the atomically thin Pt nanolayer catalyst showed superior coke-resistance(no deactivation for 24 h),high activity(turnover frequencies(TOFs)of 0.4–1.2 s^(-1)),and selectivity(>95%)toward ethylene and propylene.The unique Pt nanolayer has a similar geometric surface to Pt nanoparticles,enabling the investigations of the electronic effect on the catalytic performance,where the geometric effect is negligible.It is found that the electronic effect plays a critical role in dehydrogenative product selectivity and catalyst stability.The metal–support interaction is found dependent on the substrate and metal components,providing wide opportunities to explore high-performance MXene-supported metallic catalysts.

Catalytic alkane dehydrogenations

Olefins find widespread applications in the synthesis of polyolefins and fine chemicals. With an increasing demand for olefins, the technologies for alkane dehydrogenation have drawn much attention. Several types of heterogeneous catalysts have found applications in industry for the dehydrogenation of light alkanes, mainly ethane, propane, and butane. In the past three decades, a number of transition-metal complexes,particularly pincer-ligated iridium complexes, have been developed as the homogeneous catalysts for alkane dehydrogenations. The homogeneous catalyst systems operate under much milder conditions compared with the heterogeneous systems, and some systems exhibit good activity and high regioselectivity in dehydrogenation of alkanes longer than butane.

异戊烷脱氢生成单烯烃的热力学分析及试验研究

计算了异戊烷脱氢生成各种单烯烃主反应的热力学平衡参数及理论异戊烷平衡转化率,对产物分布规律及温度、压力、氢烃摩尔比对平衡的影响进行了分析,并通过试验研究了工艺条件对Pt-Sn-M Al_(2)O_(3)(M为助剂)催化剂性能和异戊烷脱氢产物分布的影响。试验结果表明,异戊烷脱氢生成的烯烃产物以2-甲基-2-丁烯为最多,其次为2-甲基-1-丁烯,3-甲基-1-丁烯最少。高温、低压及低氢烃摩尔比有利于脱氢反应的进行,但温度过高会导致裂解等副反应增多,使烯烃的选择性下降;压力过低及氢烃摩尔比过小均会使催化剂的积炭速率增大。异戊烷脱氢反应的实际转化率均低于热力学计算所得的平衡转化率,通过选择合适的反应条件,可使异戊烷脱氢反应的实际转化率接近热力学平衡转化率,验证了热力学分析结果的可靠性。

Synthesis and characterization of a tetradentate PNCP iridium complex for catalytic alkane dehydrogenation

A novel hydrido iridium chloride complex supported by a tetradentate PNCP ligand has been synthesized and characterized. Upon activation with NaOtBu, the PNCP-IrHC1 complex is active for transfer dehydrogenation of cyclic and linear alkanes.

纳米碳材料在低碳烷烃直接脱氢中应用的研究进展

低碳烷烃直接脱氢是生产低碳烯烃的重要方式,其关键在于催化剂。纳米碳材料原料来源广泛、存在形式多样且结构可调变性强,获得了研究者们的广泛关注。基于纳米碳材料在低碳烷烃直接脱氢领域中的研究现状,总结了纳米碳催化剂及以纳米碳材料为载体的Pt/纳米碳催化剂催化低碳烷烃直接脱氢的反应机理,分析了元素掺杂、缺陷改性和形貌调控这3种修饰方式对纳米碳催化剂及Pt/纳米碳催化剂的电子结构、几何形貌及其脱氢性能的影响。未来可以结合原位表征和理论计算深入研究修饰方式的作用机理,指导制备脱氢性能优异的纳米碳催化剂及Pt/纳米碳催化剂,并通过系统研究催化剂成型及再生工艺推动催化剂的工业化应用。

Thermocatalytic Dehydrogenation-Enabled Arene-Alkane Couplings

Comprehensive Summary The direct use of non-prefunctionalized arene and alkane as the starting materials to construct Caryl−Calkyl bond is an unfulfilled target and approaches to this challenge rarely surface in methodology studies.Current methods for thermocatalytic arene-alkane couplings(AAC)occur with specific substrates and/or inconvenient reagents.Herein,we report a one-pot relay bicatalysis system for AAC involving(pincer)Ir-catalyzed alkane transfer dehydrogenation and Fe(OTf)3-catalyzed olefin hydroarylation.This system exhibits broad scope and is particularly effective for alkylation of arenes with arylalkanes to form 1,1-diarylalkanes with high chemo-and regioselectivity,making it potentially useful for late-stage alkylation of complex molecules.Experimental mechanistic data provide a view into the factors controlling the regioselectivity.Finally,the strategy of dehydrogenation-enabled arene-alkane couplings has been successfully extended to a tandem catalysis by using a heterogeneous olefin hydroarylation catalyst.

东芝三菱变频器软启动同步切换技术在京博石化烷烃脱氢装置压缩机的应用

本文简单叙述了对京博石化烷烃脱氢装置进行的技术改造,将原东芝三菱变频运行用的高压变频器,改造为变频运行加上能软启动同步切换的变频器,可以将电机无扰切换到电网上工频运行。简单叙述了改造的必要性,改造的基本思路和方案,以及改造后的实际效果。