Carbon-Doped BN Nanosheets for the Oxidative Dehydrogenation of Ethylbenzene

Carbon-based catalysts have demonstrated great potential for the aerobic oxidative dehydrogenation reaction (ODH). However, its widespread application is retarded by the unavoidable deactivation owing to the appearance of coking or combustion under ODH conditions. The synthesis and characterization of porous structure of BCN nanosheets as well as their application as a novel catalyst for ODH is reported. Such BCN nanosheets consist of hybridized, randomly distributed domains of h-BN and C phases, where C, B, and N were confirmed to covalent bond in the graphene-like layers. Our studies reveal that BCN exhibits both high activity and selectivity in oxidative dehydrogenation of ethylbenzene to styrene, as well as excellent oxidation resistance. The discovery of such a simple chemical process to synthesize highly active BCN allows the possibility of carbocatalysis to be explored.     

Surface Chemistry and Catalytic Reactivity of Borocarbonitride in Oxidative Dehydrogenation of Propane

Borocarbonitride (BCN) materials are newly developed oxidative dehydrogenation catalysts that can efficiently convert alkanes to alkenes. However, BCN materials tend to form bulky B₂O₃ due to over-oxidation at the high reaction temperature, resulting in significant deactivation. Here, we report a series of super stable BCN nanosheets for the oxidative dehydrogenation of propane (ODHP) reaction. The catalytic performance of the BCN nanosheets can be easily regulated by changing the guanine dosage. The control experiment and structural characterization indicate that the introduction of a suitable amount of carbon could prevent the formation of excessive B₂O₃ from BCN materials and maintain the 2D skeleton at a high temperature of 520 °C. The best-performing catalyst BCN exhibits 81.9 % selectivity towards olefins with a stable propane conversion of 35.8 %, and the propene productivity reaches 16.2 mmol h⁻¹ g⁻¹, which is much better than hexagonal BN (h-BN) catalysts. Density functional theory calculation results show that the presence of dispersed rather than aggregated carbon atoms can significantly affect the electronic microenvironment of h-BN, thereby boosting the catalytic activity of BCN.     

Metal‐Free Dehydrogenation of N‐Heterocycles by Ternary h‐BCN Nanosheets with Visible Light

An efficient metal‐free catalytic system has been developed based on hexagonal boron carbon nitride (h‐BCN) nanosheets for the dehydrogenation of N‐heterocycles with visible light; hydrogen gas is released in the process, and thus no proton acceptor is needed. This acceptorless dehydrogenation of hydroquinolines, hydroisoquinolines, and indolines to the corresponding aromatic N‐heterocycles occurred in excellent yield under visible‐light irradiation at ambient temperature. With h‐BCN as the photocatalyst and water as the solvent, this environmentally benign protocol shows broad substitution tolerance and high efficiency.     

Catalytic Conversion of Methanol by Oxidative Dehydrogenation

This study investigates the effects of addition of oxygen on the oxidative dehydrogenation (ODH) of methanol when a fluorotetrasilicic mica ion-exchanged with palladium (Pd2 -TSM) was used as the catalyst. The reaction proceeded at a very low temperature in the presence of oxygen, and HCOOCH3 was obtained at high selectivity. By calculating the equilibrium conversion, it has been shown that substantial ODH took place for HCOOCH3 production. Consequently, this reaction would make dehydrogenation the dominant reaction at equilibrium. Not all the H dissociated from CH3OH was converted to H2O by oxidation. It has been shown that the H2O was not produced from oxidative dehydrogenation by the direct reaction of CH3OH and O2 when an attempt was made to carry out oxidative dehydrogenation using an isotope oxygen trace method in the gas phase. Therefore, when CH3OH was converted to CO2 and dehydrogenated to HCOOCH3, the C—O bonds were not dissociated.     

Ytterbium-Containing Oxide Catalysts for Oxidative Dehydrogenation of Hydrocarbons

Oxide catalyst samples for the oxidative dehydrogenation (ODH) of alkanes were prepared by heat treatment of precursors, namely, hydrotalcite-related magnesium aluminum double hydroxo salts containing ytterbium, as well as magnesium, aluminum, chromium, vanadium, molybdenum, and niobium in various combinations. Their catalytic activities were studied. Some catalysts were found to have high efficiency in ODH of ethane, propane, and isobutane, increasing the product yield and enhancing the reaction selectivity.     

Few‐Layer Borocarbonitride Nanosheets: Platinum‐Free Catalyst for the Oxygen Reduction Reaction

The present study demonstrates the use of few‐layer borocarbonitride nanosheets synthesized by a simple method as non‐platinum cathode catalysts for the oxygen reduction reaction (ORR) in alkaline medium. Composition‐dependent ORR activity is observed and the best performance was found when the composition was carbon‐rich. Mechanistic aspects reveal that ORR follows the 4 e^? pathway with kinetic parameters comparable to those of the commercial Pt/C catalyst. Excellent methanol tolerance is observed with the BCN nanosheets unlike with Pt/C.     

Acid/Vanadium‐Containing Saponite for the Conversion of Propene into Coke: Potential Flame‐Retardant Filler for Nanocomposite Materials

Vanadium‐containing saponite samples were synthesized in a one‐pot synthetic procedure with the aim of preparing samples for potential application as fillers for polymeric composites. These vanadium‐modified materials were prepared from an acid support by adopting a synthetic strategy that allowed us to introduce isolated structural V species (H/V‐SAP). The physicochemical properties of these materials were investigated by XRD analysis and by DR‐UV/Vis and FTIR spectroscopy of CO that was adsorbed at 100 K; these data were compared to those of a V‐modified saponite material that did not contain any Brønsted acid sites (Na/V‐SAP). The surface‐acid properties of both samples (together with the fully acidic H‐SAP material and the Na‐SAP solid) were studied in the catalytic isomerization of α‐pinene oxide. The V‐containing solids were tested in the oxidative dehydrogenation reaction of propene to evaluate their potential use as flame‐retardant fillers for polymer composites. The effect of tuning the presence of Lewis/Brønsted acid sites was carefully studied. The V‐containing saponite sample that contained a marked presence of Brønsted acid sites showed the most interesting performance in the oxidative dehydrogenation (ODH) reactions because they produced coke, even at 773 K. The catalytic data presented herein indicate that the H/V‐SAP material is potentially active as a flame‐retardant filler.     

FeVO4催化剂的原位电导研究

采用盐类固体研磨法制备了FeVO4催化剂,用原位电导方法测定了FeVO4催化剂在氧气 丙烷→氧气→丙烷连续变化气氛下的电导变化,确定其导电类型.以BET、XRD、H2-TPR等技术对催化剂进行表征,研究了其对丙烷氧化脱氢制丙烯反应的催化性能.     

A Team for the Development of Next-Generation Metal-Free Catalysis

This invited Team Profile was created by the Xie and Lin groups, hailing from the Key Laboratory of Advanced Carbon-Based Functional Materials (Fujian Province University) and the State Key Laboratory of Photocatalysis on Energy and Environment within the College of Chemistry at Fuzhou University (China). They recently published an article on borocarbonitride (BCN) nanosheets derived from the biomolecule guanine, which proved to be efficacious catalysts in the oxidative dehydrogenation of propane (ODHP). This work provides new insight into the role of carbon in BCN catalysts and provides principles for the design of stable boron-based catalysts. “Surface Chemistry and Catalytic Reactivity of Borocarbonitride in Oxidative Dehydrogenation of Propane”, G. Wang, S. Chen, Q. Duan, F. Wei, S. Lin, Z. Xie, Angew. Chem. Int. Ed. 2023 , 62, e202307470 .     

B‐MWW Zeolite: The Case Against Single‐Site Catalysis

Boron‐containing materials have recently been identified as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins. It has previously been demonstrated by several spectroscopic characterization techniques that the surface of these boron‐containing ODH catalysts oxidize and hydrolyze under reaction conditions, forming an amorphous B₂(OH)_xO_(3?x/2) (x=0–6) layer. Yet, the precise nature of the active site(s) remains elusive. In this Communication, we provide a detailed characterization of zeolite MCM‐22 isomorphously substituted with boron (B‐MWW). Using ¹¹B solid‐state NMR spectroscopy, we show that the majority of boron species in B‐MWW exist as isolated BO₃ units, fully incorporated into the zeolite framework. However, this material shows no catalytic activity for ODH of propane to propene. The catalytic inactivity of B‐MWW for ODH of propane falsifies the hypothesis that site‐isolated BO₃ units are the active site in boron‐based catalysts. This observation is at odds with other traditionally studied catalysts like vanadium‐based catalysts and provides an important piece of the mechanistic puzzle.     

烷烃脱氢制烯烃用碳催化剂的微结构和表面化学调控研究进展(英文)

烯烃是重要的大宗有机化工原料,广泛用于塑料、树脂、橡胶等高分子材料和基础有机化工产品和中间体的生产.同时,烯烃也是重要的精细化工原料和中间体,广泛用于染料、医药、香料、农用化学品、水性油墨和感光树脂等精细化工领域.长链烯烃通常是由小分子烯烃聚合制得,而小分子烯烃和苯乙烯的合成在学术界和工业界备受关注.在脱氢、裂解、脱水等诸多合成方法中,烷烃脱氢制烯烃是直接而中的路线,包括直接脱氢和氧化脱氢.小分子烷烃和乙苯催化脱氢制备对应的烯烃,尤其是乙苯制苯乙烯,目前工业上主要采用铁基催化剂催化直接脱氢工艺.积炭失活是该工艺面临的严峻挑战.工业上采用引入大量过热水蒸气的方法来解决这一难题,同时,还可以为脱氢反应提供热量.但是,这势必造成巨大的能耗和反应器容积效率的显著降低.氧化脱氢工艺是放热反应,并可有效抑制积炭,但又存在过氧化所致的低选择性的问题.直接脱氢和氧化脱氢各有利弊.目前,科学家和工业界都在扬长避短,开展两种脱氢工艺的新结构高性能催化剂的研究,并取得了长足进展.碳催化是近年来发展起来的一类重要的无机非金属固相催化剂,在光催化、电催化,以及热催化领域得到了广泛关注同时也是材料领域研究的前沿和热点.碳材料,尤其是纳米碳,在诸多反应中展示出了比常规金属催化剂更好的催化性能,且具有可持续的特征.因此,碳催化具有广阔的发展空间和巨大的应用前景.众所周知,固体催化剂的催化性能重要依赖于催化剂表面催化活性位的性质及其可及性.元素组成、化学状态及缺陷边角特征决定着活性位的性质,而形貌、尺寸、形状、纹理、表面结构等催化剂的微结构特征决定着固相催化剂活性位的可及性.因此,探索有效的方法和策略,来调节固相催化剂的微结构和表面化学性质,已成为催化学术研究的热点领域.碳材料的表界面和边角的官能团和结构缺陷是催化反应的活性位.对于烷烃脱氢反应,碳材料的表界面羰基和结构缺陷是催化剂的活性位,而杂原子掺杂可以调控活性位的电子结构.本文综述了烷烃脱氢用碳催化剂微结构和表面化学调控方法和效果的最新研究进展,并讨论了烷烃脱氢碳催化材料的微结构和表面化学性质调控的重要性和严峻挑战.通过碳材料合成中前驱体的优选、合成方法和策略的创新,以及通过后处理的方法,均可有效调控碳催化剂的微结构和表面化学性质,从而调控其烷烃脱氢催化性能.碳催化用于烷烃脱氢反应制烯烃,尤其是直接脱氢,前景看好.目前,研究的碳催化剂多为粉末状,用于固定床,存在流体阻力大、压力降高、操作困难的问题,并有可能阻塞床层,造成安全隐患;用于流化床,粉末碳易于团聚,催化剂过滤分离困难,流失严重.纳米碳基整体式催化剂可以是碳催化的未来发展方向.但是,目前才刚刚起步.碳基整体式催化剂活性单元本身可及活性位的性质及活性单元的分散性、抗脱落性和整体式催化剂的机械强度、导热性等诸多问题需要深入研究和探讨.总之,碳催化烷烃脱氢,尤其是无氧化剂、无水蒸气条件下的直接脱氢,是经济、节能、清洁、高效的烯烃生产方法,具有广阔的发展空间和美好前景.微结构和化学性质的调变是调控固相催化剂催化活性位性质和可接近性的重要方法,碳催化材料及整体式催化剂的碳基活性单元微结构和化学性质的调控是实现其催化性能调控的有效策略.     

Ytterbium-Containing Magnesium–Aluminum Hydroxo Salts with a Hydrotalcite-Type Structure

A method is developed for inserting ytterbium into Mg–Al hydroxo salts that have a hydrotalcitetype layered structure, as well as for the chemical analyses of complex hydroxo salts containing ytterbium in various combinations with magnesium, aluminum, chromium, vanadium, molybdenum, and niobium. The formation conditions of these hydroxo salts have been studied by potentiometric titration, their samples have been prepared, and X-ray diffraction patterns recorded. The prepared hydroxo salt samples have been tested as precursors for oxide catalysts of oxidative dehydrogenation (ODH) of alkanes.     

Highly efficient VOx/SBA-15 mesoporous catalysts for oxidative dehydrogenation of propane

Highly dispersed vanadia species on SBA-15 mesoporous silica have been found to exhibit a highly efficient catalytic performance for the oxidative dehydrogenation (ODH) of propane to light olefins (propene + ethylene).     

Oxidative Dehydrogenation of <Emphasis Type="Italic">n</Emphasis>-Butenes to 1,3-Butadiene over Bismuth Molybdate and Ferrite Catalysts: A Review

1,3-Butadiene, an important raw material for a variety of chemical products, can be produced via the oxidative dehydrogenation (ODH) of n-butenes over multicomponent oxide catalysts based on bismuth molybdates and ferrites. In this review, the basic concept, reaction mechanism, and catalysts typically used in an ODH reaction are discussed.     

Europium oxide containing catalysts for oxidative dehydrogenation of alkanes

A method is developed to incorporate europium into Mg–Al hydrotalcites, which are precursors for oxide catalysts of oxidative dehydrogenation (ODH) of alkanes; samples of oxide catalysts are prepared, where europium oxide and gallium, magnesium, aluminum, chromium, vanadium, molybdenum, and niobium oxides are contained in various combinations. The catalytic properties of these catalysts in the reactions of ethane, propane, and butane ODH are studied. The incorporation of europium into some of our studied multicomponent catalysts enhances the reaction selectivity and increases yields of desired products.     

CH bond activation in the presence or absence of oxygen or nitrous oxide

The reaction of C₂H₆with lattice oxygen, O^2- (in the absence of gaseous oxygen), or “adsorbedℍ oxygen (in the presence of gaseous oxygen) over NiMoO₄ catalysts has been performed and compared to C₃H₈ activation. The results obtained indicate that adsorbed oxygen exhibits a higher reactivity to C₂H₆, while lattice oxygen is more reactive relative to C₃H₈. Kinetic studies of these two reactions in presence of molecular oxygen have indeed shown that the ethane oxidative dehydrogenation (ODH) is dependent on the oxygen partial pressure, whilst on the contrary propane ODH is not. In order to confirm the presence of “adsorbed” oxygen for ethane activation, ODH tests have been performed with N₂O. On increasing temperature, the O^- adsorbed species enhances the mild oxidation of ethane. The activation energy of ethane consumption E_C2H6, relative to propane (E_C3H8 = 133 kJ/mol) is 145 kJ/mol. A possible mechanism is proposed for the oxidative dehydrogenation of ethane. This revised version was published online in August 2006 with corrections to the Cover Date.     

Praseodymium-containing catalysts for oxidative dehydrogenation of organic compounds

A method is developed for incorporating praseodymium into magnesium–aluminum hydrotalcites, which are precursors for oxide catalysts for oxidative dehydrogenation (ODH) of alkanes. Oxide catalyst samples that contain praseodymium and various combinations of magnesium, aluminum, chromium, vanadium, molybdenum, and niobium are prepared. The catalytic properties of the prepared catalysts in ethane, propane, and butane ODH reactions are studied. Into some of our studied multicomponent catalysts, the incorporation of praseodymium enhances the reaction selectivity and increases yields of desired products.     

Oxidative dehydrogenation of <Emphasis Type="Italic">n</Emphasis>-butane on nano-carbon catalysts having graphitic structures

The catalytic activity of well-nanostructured carbon, for example glassy carbon spheres, SWCNT, graphene, and graphite, has been demonstrated in the oxidative dehydrogenation (ODH) of butane to obtain olefins. The catalytic performance of the carbon samples was stable, with prolonged reaction time. The proportion of butenes in the product decreased as the reaction temperature increased, whereas selectivity for ethene and propene increased with increasing temperature. Pd-containing carbon nanofibers (CNF) had superior selectivity for butadiene formation than Pd free CNF catalyst. Carbon with graphitic structures was highly selective for propylene and butenes without severe combustion in ODH of butane.