Catalysts For Dehydrogenation Of Propane Research Articles

Identifying the Active Phase on Atomically Dispersed Catalysts for Propane Dehydrogenation: Positively Charged vs Metallic Transition Metals

Identifying the Active Phase on Atomically Dispersed Catalysts for Propane Dehydrogenation: Positively Charged vs Metallic Transition Metals

Influence of the Severity of Reaction Conditions on the Promotional Effects of Tin in Pt–Sn/γ-Al2O3 Catalysts in Propane Dehydrogenation

Influence of the Severity of Reaction Conditions on the Promotional Effects of Tin in Pt–Sn/γ-Al2O3 Catalysts in Propane Dehydrogenation

Silicon Nitride Surface Enabled Propane Dehydrogenation Catalyzed by Supported Organozirconium.

Mesoporous silicon nitride (Si3N4) is a nontraditional support for the chemisorption of organometallic complexes with the potential for enhancing catalytic activity through features such as the increased Lewis basicity of nitrogen for heterolytic bond activation, increased ligand donor strength, and metal-ligand orbital overlap. Here, tetrabenzyl zirconium (ZrBn4) was chemisorbed on Si3N4, and the resulting supported organometallic species was characterized by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Dynamic Nuclear Polarization-enhanced Solid State Nuclear Magnetic Resonance (DNP-SSNMR), and X-ray Absorption Spectroscopy (XAS). Based on the hypothesis that the nitride might enable facile heterolytic C-H bond activation along the Zr-N bond, this material was found to be a highly active (1.53 molpropene molZr-1 h-1 at 450 °C) and selective (99% to propylene) catalyst for propane dehydrogenation. In contrast, the homologous silica supported complex exhibited negligible activity under these conditions.

In Situ Formation of Platinum-Carbon Catalysts in Propane Dehydrogenation.

The catalytic production of propylene via propane dehydrogenation (PDH) is a key reaction in the chemical industry. By combining operando transmission electron microscopy with density functional theory analysis, we show that the intercalation and ordering of carbon on Pt interstitials to form Pt-C solid solutions is relevant for increasing propylene production. More specifically, we found that at the point of enhanced propylene formation, the structure of platinum nanoparticles is transformed into a transient caesium chloride-type Pt-C polymorph. At more elevated temperatures, the zincblende and rock salt polymorphs seemingly coexist. When propylene production was highest, multiple crystal structures consisting of Pt and carbon were occasionally found to coexist in one individual nanoparticle, distorting the Pt lattice. Catalyst coking was detected at all stages of the reaction, but did initially not affect all particles. These findings could lead to the development of novel synthesis strategies towards tailoring highly efficient PDH catalysts.

In Situ Formation of Platinum‐Carbon Catalysts in Propane Dehydrogenation

AbstractThe catalytic production of propylene via propane dehydrogenation (PDH) is a key reaction in the chemical industry. By combining operando transmission electron microscopy with density functional theory analysis, we show that the intercalation and ordering of carbon on Pt interstitials to form Pt−C solid solutions is relevant for increasing propylene production. More specifically, we found that at the point of enhanced propylene formation, the structure of platinum nanoparticles is transformed into a transient caesium chloride‐type Pt−C polymorph. At more elevated temperatures, the zincblende and rock salt polymorphs seemingly coexist. When propylene production was highest, multiple crystal structures consisting of Pt and carbon were occasionally found to coexist in one individual nanoparticle, distorting the Pt lattice. Catalyst coking was detected at all stages of the reaction, but did initially not affect all particles. These findings could lead to the development of novel synthesis strategies towards tailoring highly efficient PDH catalysts.

Liquid Gallium–Zeolite Nanocomposite Catalysts for Propane Dehydrogenation

Liquid Gallium–Zeolite Nanocomposite Catalysts for Propane Dehydrogenation

P-modified Pt/Al2O3 catalysts for selective propane dehydrogenation

The rigorous operating conditions required for propane dehydrogenation result in undesired side reactions on Pt catalysts. Herein, we present the successful suppression of structure-sensitive side reactions by modifying Pt/Al2O3 catalysts with P. The characterization of the P-modified Pt/Al2O3 catalysts revealed the coexistence of metallic Pt and Pt–P alloys on the surfaces of the Pt nanoparticles. At a reaction temperature of 600 °C, the Pt catalyst modified with an optimal amount of P exhibited a notably higher propylene selectivity (95%) than that of the unmodified Pt/Al2O3 catalyst (typically ∼83%), without any loss of activity. A detailed investigation revealed that the geometric effect resulting from the formation of the Pt–P alloy, which reduced the size of the Pt ensembles, was mainly responsible for the enhanced performance of P-modified Pt/Al2O3. This study offers vital insights into the formation of noble metal–P alloys on nanoparticle surfaces and their advantageous effects on heterogeneous catalysis.

Modulation of metal–support interactions in Pt–TiOx synergistic catalysts for propane dehydrogenation

The strong metal-support interaction exerts a significant influence on the catalytic performance of the metal active site. This paper describes the modulation of the coverage of TiOx on the Pt nanoparticles via the pretreatment atmosphere, and its influence of the catalytic performance for propane dehydrogenation. The direct reduction in H2 at 600 °C of the Pt/TiO2-Al2O3 catalyst induces partial coverage of the Pt nanoparticles by TiOx. This partial coverage with TiOx leads to higher electron density over platinum than catalysts through air calcination followed by reduction, which can enhance the selectivity of propylene. Furthermore, the presence of TiOx in the catalysts can promote C–H activation during propane dehydrogenation. Eventually, this synergistic catalyst presents a high formation rate of propylene (141.1 mmol·gcat-1·h−1) and propylene selectivity of ∼ 91 % with a low deactivation rate of 0.09 h−1. This study unveils an effective approach to modulate the catalytic performance of metals supported on oxides based on metal-support interaction.

Acid-leaching treated ZnO-based materials as highly efficient microwave catalysts for oxidative dehydrogenation of propane by CO2

The oxidative dehydrogenation of propane by CO2 (CO2-ODHP) reaction has received much attention for its potential to produce high-value propylene from two underutilized reactants and to eliminate CO2. However, it is a great challenge to maintain high propylene selectivity with high propane conversion for CO2-ODHP reaction, especially for non-expensive and environmentally friendly catalysts. Herein, a new and effective ZnO/S-1(1.0)-based microwave catalyst for CO2-ODHP was developed by a simple impregnation method and acid leaching treatment. Interestingly, the acid leaching treatment significantly enhanced the catalytic activity and stability. Importantly, both the conversion of propane and the selectivity of propylene were significantly enhanced in the microwave catalytic reaction mode (MCRM). An amazingly high conversion of ∼60 % and selectivity of ∼92 % is achieved. This method of significantly improving the catalytic activity and stability after a simple acid leaching treatment can provide some inspiration for light alkane dehydrogenation reactions.

Nano-Hierarchical SSZ-13-Supported Low-Polymerized VOX as Highly Efficient Catalysts for Propane Dehydrogenation

Nano-Hierarchical SSZ-13-Supported Low-Polymerized VO_X as Highly Efficient Catalysts for Propane Dehydrogenation

Copper-Promoted Platinum Supported on HSSZ-13 Zeolite Catalysts for Propane Dehydrogenation to Propylene

Copper-Promoted Platinum Supported on HSSZ-13 Zeolite Catalysts for Propane Dehydrogenation to Propylene

Propane dehydrogenation over zinc-on-zirconia catalyst via atom trapping

Propylene is an important resource for large petrochemicals production. Propane dehydrogenation (PDH), which directly produces propylene while producing hydrogen as a by-product, has attracted extensive attention in recent years. Among various PDH catalysts, Zn-based catalyst has great potentials in industrial implementation because of its low cost and eco-friendly. Herein, we synthesized Zn–O–Zr active center via atom trapping strategy for effectively catalyzing PDH reaction. The ability of phase transition upon Zn deposition is supposed to be a possible indicator to assess active degree of ZrO2, which is directly related to the proportion of surface absorbed oxygen species (SAOS) on ZrO2. We demonstrate that SAOS concentration can be promoted through stabilizing tetragonal-phase and doping Hf, results in more Zn–O–Zr species, lower active energy, and easier phase transition. This study reveals the electronic effect on atom trapping process used in Zn–ZrO2 system and provides guidance to design and prepare high-performance Zn-based PDH catalysts.

Optimizing propylene selectivity and stability over Pt–Sn/MgAl2O4 catalysts for propane dehydrogenation

Optimizing propylene selectivity and stability over Pt–Sn/MgAl2O4 catalysts for propane dehydrogenation

Sulfur-doped Pt/C catalyst for propane dehydrogenation with improved atomic utilization and stability

Atomically well-dispersed platinum catalysts play a vital role in various chemical processes such as direct dehydrogenation of propane (PDH), due to their high performance originated from high atom utilization. However, these catalysts suffer from complex preparation methods, and preparing atomically dispersed Pt-based catalysts with feasible methods remains challenging. Herein, we report a convenient method to prepare efficient atomically dispersed Pt/C catalysts for PDH by sulfur doping into the carbon support by simple cyclohexane impregnation method. The prepared atomically well-dispersed catalysts possess strong interactions between Pt and carbon support, which led to improved exposure of active sites and higher propylene formation rate compared to that without sulfur doping. Sintering of the Pt species was also inhibited and stability was improved by 47%. Propylene selectivity also showed a positive correlation with the amount of sulfur doping. The propane conversion first increased and then decreased, which was due to the loss of sulfur during the reaction that caused the agglomeration of Pt and the evolution of structure. It was found that the maximum catalytic activity appeared with Pt clusters of ∼ 0.71 nm with an average Pt-Pt coordination number of 3.1 and Pt-Pt bond distance of 3.09 Å.

The impact of indium and manganese modifiers on the catalytic properties of zinc-alumina propane dehydrogenation catalysts

Supported zinc-containing catalysts are considered as a viable alternative to the currently-deployed Cr-based (toxic) and Pt-based (costly) catalysts of alkane dehydrogenation, as reflected also in the increased number of reports related to the Zn-based catalysts in recent years. Here, we present a study of alumina-supported Zn-In and Zn-Mn propane dehydrogenation (PDH) catalysts prepared by the tailored methods. Specifically, the introduction of zinc relied on the chemical vapor deposition (CVD, using Zn vapor) onto alumina or alumina-supported indium or manganese materials, the latter two prepared by the impregnation of alumina with aqueous solutions of the respective metal nitrates followed by the calcination and hydrogen treatment. Alternatively, both zinc and indium were introduced by the co-impregnation of alumina with aqueous zinc and indium nitrates. The PDH tests revealed that the “dilution” of the active Zn2+ surface sites with In+ cations lead to a significant improvement in the catalytic performance, i.e., the introduction of In+ increased propene selectivity and attenuated the undesirable cracking and hydrogenolysis side reactions as well as decreased coke formation. In contrast, Mn2+ cations improved the catalytic properties of Zn2+ surface sites to a lesser extent than In+ cations. All prepared catalysts were characterized by DRIFT (diffuse reflectance infrared Fourier transform) spectroscopy of the adsorbed CO and H2 probe molecules. It was found that surface In+ and Mn2+ cations affect Zn2+ sites (electronic and geometric effect), which can be assessed from the position of the IR bands of zinc hydridespecies, formed due to the heterolytic hydrogen dissociation on the Zn2+ active sites. The effect of In and Mn dopants also was confirmed by the molecular DFT simulation.

Understanding the mechanism of propane dehydrogenation over coordinatively unsaturated Co-O acid-base pairs and the inhibition effect of trace oxygen

High temperature and a reducing atmosphere are characteristic of propane dehydrogenation (PDH) reaction. Under such condition, the real surface structure of catalysts often differs from that in the ambient environment, particularly for CoOx species with multiple valence states and coordination. Here, a combination of in situ/operando Raman spectroscopy, in situ UV–Vis diffuse reflectance spectroscopy (DRS), and density functional theory (DFT) calculations reveal that coordinatively unsaturated Co-O (Cocu-O) acid-base pairs via lattice oxygen consumption are the PDH active sites of CoOx/Al2O3 catalysts. This highly dispersed Cocu-O species exhibit a C3H6 formation rate and C3H6 selectivity as high as 2 mmol‧gcat−1‧min−1 and 95 %, respectively, which is comparable to most state-of-the-art CoOx-based catalysts. However, industrial C3H8 raw gases typically contain 10–1000 ppm oxygen gas, and the complete eliminating oxygen increases costs. PDH catalytic performance of CoOx/Al2O3 catalysts is sensitive to the extremely low concentration of oxygen gas and is significantly inhibited by it. The fundamental reason is that the concentration of Cocu active sites is determined by the competitive reaction between the filling of trace oxygen on oxygen vacancies and lattice oxygen consumption. The reaction rate of the former is significantly higher than that of the latter. The higher reducibility of CoOx species leads to relatively weaken inhibition of trace oxygen for PDH activity. The oxygen content in the propane feed gas is a non-negligible factor in the development of new Co-based PDH catalysts, especially for their industrial applications.

Hydrothermal synthesis of highly cross‐linked PtZn@Silicalite‐1 structured catalysts for propane dehydrogenation

AbstractStructured catalysts coatings exhibit excellent performance on non‐adiabatic gas–solid process, deriving from their enhanced heat and mass transfer properties. However, the coating catalysts prepared by traditional hydrothermal method of zeolite encapsulating noble metal are prone to spalling, especially under conditions of large flow rate and high temperature. Herein, we prepared PtZn clusters encapsulated in silicalite‐1 zeolite coating on stainless steel with high bonding strength by an improved in situ growth method. The optimized catalyst exhibited ultra‐thin, uniform, continuous, and high degree of crosslinking, thereby enhancing mass transfer and thermal stability. In propane dehydrogenation reaction, the optimized PtZn@S‐1‐R showed a high specific activity of 14.7 molPt−1 s−1 and a propylene selectivity above 99% at 600°C with a high weight hourly space velocity of 120 h−1. The metal‐encapsulated zeolite coating catalysts broaden the application avenue for heterogeneous catalysis with great application prospects.

Tricoordinated Single-Atom Cobalt in Zeolite Boosting Propane Dehydrogenation.

Propane dehydrogenation (PDH) reaction has emerged as one of the most promising propylene production routes due to its high selectivity for propylene and good economic benefits. However, the commercial PDH processes usually rely on expensive platinum-based and poisonous chromium oxide based catalysts. The exploration of cost-effective and ecofriendly PDH catalysts with excellent catalytic activity, propylene selectivity, and stability is of great significance yet remains challenging. Here, we discovered a new active center, i.e., an unsaturated tricoordinated cobalt unit (≡Si-O)CoO(O-Mo) in a molybdenum-doped silicalite-1 zeolite, which afforded an unprecedentedly high propylene formation rate of 22.6 molC3H6 gCo-1 h-1 and apparent rate coefficient of 130 molC3H6 gCo-1 h-1 bar-1 with >99% of propylene selectivity at 550 °C. Such activity is nearly one magnitude higher than that of previously reported Co-based catalysts in which cobalt atoms are commonly tetracoordinated, and even superior to that of most of Pt-based catalysts under similar operating conditions. Density functional theory calculations combined with the state-of-the-art characterizations unravel the role of the unsaturated tricoordinated Co unit in facilitating the C-H bond-breaking of propane and propylene desorption. The present work opens new opportunities for future large-scale industrial PDH production based on inexpensive non-noble metal catalysts.

Overcoming limitations in propane dehydrogenation by codesigning catalyst-membrane systems.

Propylene production through propane dehydrogenation (PDH) is endothermic, and high temperatures required to achieve acceptable propane conversions lead to low selectivity and severe carbon-induced deactivation of conventional catalysts. We developed a catalyst-membrane system that removes the hydrogen by-product and can thus achieve propane conversions that exceed equilibrium limits. In this codesigned system, a silica/alumina (SiO2/Al2O3) hollow-fiber hydrogen membrane was packed with a selective platinum-tin (Pt1Sn1/SiO2) PDH catalyst on the tube side with hydrogen diffusing from the tube to the shell side. We demonstrate that the catalyst-membrane system can achieve propane conversions >140% of the nominal equilibrium conversion with a propylene selectivity >98% without deactivation of the system components. We also show that by introducing oxygen on the shell side of the catalyst-membrane system, we can couple the endothermic PDH reaction on the tube side with exothermic hydrogen oxidation on the shell side. This coupling results in higher rates of hydrogen transport, leading to further enhancements in the propane conversion as well as desired thermoneutral system operation.

Peripheral P doping in Zn1/NC single-atom catalyst to enhance propane dehydrogenation reaction

Although Zn-based catalysts are widely used for propane dehydrogenation (PDH), the positively charged Zn is susceptible to reduction to metallic state under harsh conditions, which ultimately leads to its vaporization and thus irreversible deactivation. Moreover, the understanding of the structure-performance relationship of Zn-based catalysts in PDH remains limited. In this work, the effect of peripheral P doping on PDH over atomically dispersed Zn catalysts with different N/C coordination numbers (Zn1-NnC4-n-P, n = 2–4) is investigated by density functional theory (DFT) calculations. The results show that the peripherally P-doped Zn1-N2C2 catalyst exhibits improved performance and stability compared to the undoped Zn1-N2C2. It is revealed that there is a linear relationship between the energy barrier of the first dehydrogenation step of C3H8 and the H affinity of the active site. Furthermore, the peripheral P doping contributes to the stabilization of the tetra-coordination structure of Zn during catalysis, which in turn lowers the energy barrier for the second dehydrogenation step of C3H8. The experimental results are in good agreement with theoretical predictions. This work provides useful insights for the rational design of efficient SACs for PDH via doping strategy.