Propane Dehydrogenation Reaction Research Articles

Synthesis of Ordered Mesoporous Molecular Sieve-Supported Cobalt Catalyst via Organometallic Complexation for Propane Non-Oxidative Dehydrogenation.

Co-based catalysts have shown great promise for propane dehydrogenation (PDH) reactions due to their merits of environmental friendliness and low cost. In this study, ordered mesoporous molecular sieve-supported CoOx species (CoOx/Al-SBA-15 catalyst) were prepared by one-step organometallic complexation. The catalysts show worm-like morphology with regular straight-through mesoporous pores and high external specific surface area. These typical features can substantially enhance the dispersion of CoOx species and mass transfer of reactants and products. Compared with the conventional impregnation method, the 10CSOC (10 wt.% Co/Al-SBA-15 prepared by the organometallic complexation method) sample presents a smaller CoOx size and higher Co2+/Co3+ ratio. When applied to PDH reaction, the 10CSOC delivers higher propane conversion and propylene selectivity. Under the optimal conditions (625 °C and 4500 h-1), 10CSOC achieves high propane conversion (43%) and propylene selectivity (83%). This is attributed to the smaller and better dispersion of CoOx nanoparticles, more suitable acid properties, and higher content of Co2+ species. This work paves the way for the rational design of high-performance catalysts for industrially important reactions.

Kinetic study of propane ODH on electrospun vanadium oxide-based submicron diameter fiber catalyst

A rigorous kinetic study of the oxidative dehydrogenation (ODH) reaction of propane on a vanadium oxide-based submicron diameter fiber catalyst has been developed. The proposed kinetic model simulates the conversion-selectivity profiles, the surface coverage of the different adsorbed species and the oxidation state of the catalyst for the studied operating conditions of temperature, space–time and inlet partial pressures of propane and oxygen. The activation energy of the rate determining step (RDS), the first hydrogen abstraction from propane, is 104 kJ·mol−1. The model predicts that although the reaction seems to be pseudo-zero order with respect to oxygen in a broad range of conditions, the catalyst may not be fully oxidized during reaction. The accuracy of the model when predicting the oxidation state of the catalyst has been experimentally confirmed by analyzing the catalytic fixed bed after reaction. The reduction degree of the catalyst will depend on its intrinsic chemical nature and reaction conditions, increasing with the space–time and in detriment of the overall reaction rate. Consequently, the propane turnover frequency (TOF) will also depend on the reaction conditions and space–time, even changing along the fixed-bed reactor.

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.

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.

The enhancing effect of Co2+ on propane non-oxidative dehydrogenation over supported Co/ZrO2 catalysts

Due to the increased production of shale gas containing propane, the share of non-oxidative propane dehydrogenation (PDH) in the large-scale production of propene is expected to continue to grow. There are, however, some ecofriendly and cost shortcomings associated with the currently applied Cr- or Pt-containing catalysts. Against this background, we present here Co/ZrO2 alternatives and reveal the fundamentals affecting their activity, which can be used for purposeful catalyst design. Co2+ species homogeneously distributed within the lattice of ZrO2 significantly increase the activity of coordinatively unsaturated Zr4+ for the PDH reaction. The increase is caused by accelerating both the cleavage of CH bonds in propane and the recombination of surface H species, with the latter reaction being the rate-limiting step. The best-performing catalyst outperformed an analogue of commercial K-CrOx/Al2O3 in terms of the rate of propene formation and demonstrated durable performance over a series of 10 PDH/regeneration cycles under industrially relevant conditions. It also outperformed most previously developed Co-containing catalysts in terms of propene productivity. The space–time yield of propene formation achieved at 57 % equilibrium propane conversion at 550 °C was 0.71 kg·h−1·kgcat-1.

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.

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)3Sn–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 dehydrogenation 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.

Catalytic propane dehydrogenation by anatase supported Ni single-atom catalysts

With the increasing production of propane from shale gas and the growing demand for propylene, propane dehydrogenation (PDH) has gained significant attention as a promising route for the on-purpose production of propylene. As a cheap yet efficient catalyst, Ni-based catalysts have attracted interest because of its ability to activate alkane. Single-atom catalysts (SACs) can maximize the metal atom utilization. Here, we demonstrate that anatase TiO2 supported Ni SAC (Ni1/A-TiO2) exhibits not only superior intrinsic activity and propylene selectivity but also much better stability than the corresponding Ni nanoparticle (NP) catalyst (NiNP/A-TiO2) in PDH reaction at 580 °C. The rate of propylene production on Ni1/A-TiO2 is about 1.96 molC3H6 gNi−1 h−1, about 65 times higher than that of NiNP/A-TiO2 sample (0.03 molC3H6 gNi−1 h−1). In combination of high-angle annular dark-field scanning transmission electron microscopy, in-situ diffuse reflectance infrared Fourier transform spectra, in-situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy characterizations, we confirm that the Ni SAC mainly contains individual Ni atom singly dispersed on the support in positive Ni (II) valence state. In addition, as a result of strong metal-support interaction (SMSI) between Ni NP and TiO2 carrier under reduced conditions, the Ni NPs sites are encapsulated by TiOx overlayer (~2 nm thick) thus display poor reaction performance.

Exploration of ZnO-Doped Nitrogen-Carbon Materials Derived from Polyamide-Imide for Propane Dehydrogenation

A series of ZnO-doped nitrogen-carbon materials (xZnO-N-C) with ZnO contents of 5–40% are prepared by a vacuum curing–carbonization strategy using polyamide-imide as the N-C source and zinc nitrate as the metal source for propane dehydrogenation (PDH). 20ZnO-N-C exhibits outstanding initial activity (propane conversion of 35.2% and propene yield of 24.6%) and a relatively low deactivation rate (0.071 h−1) at 600 °C. The results of detailed characterization show that small ZnO nanoparticles (5.5 nm) with high dispersion on the catalyst can be obtained by adjusting the ZnO loading. Moreover, more nitrogen-based species, especially ZnNx species, are formed on 20ZnO-N-C in comparison with 20ZnO-N-C-air prepared via curing carbonization without vacuum, which may contribute to the higher product selectivity and catalytic stability of 20ZnO-N-C. The active sites for the PDH reaction on the catalyst system are proposed to be C=O species and Zn2+ species. Moreover, the carbon deposition and the aggregation of ZnO nanoparticles are the causes of activity loss on this catalyst system.

Stable Pt catalysts anchored by Mn-SBA-15 support for propane dehydrogenation

The development of stable Pt-based catalysts is important for propane dehydrogenation process. In this work, Mn-SBA-15 supports with different Mn doping amounts were prepared by in situ hydrothermal method using citric acid and urea. Compared with Pt/SBA-15 catalyst, the significantly improved dispersion and stability of Pt on Pt/Mn-SBA-15 catalysts were demonstrated by X-ray diffraction and transmission electron microscopy results. CO DRIFT spectra analysis showed the electron transfer from Mn to Pt occurred, which led to an increase in the electron density of Pt. And the propane dehydrogenation performances over Pt/Mn-SBA-15 were enhanced significantly. Among them, the Pt/10Mn-SBA-15 shows the highest initial propane conversion of 51.2% and lowest deactivation rate constant of 0.013 h−1. The reason may be that appropriate amount of Mn can modify Pt by both electronic effect and geometric effect. And the strong metal-support interaction formed by highly dispersed MnOx anchor sites in Mn-SBA-15 support maintains the stability of Pt during the propane dehydrogenation reaction.

Promoted propane dehydrogenation over Co confined within core–shell silicalite-1 zeolite crystals

Silicalite-1 coating boosted the catalytic activity of Co-loaded silicalite-1 zeolite for propane dehydrogenation reaction.

Structure evolution of porous alumina during aging process and its support effect on PtSn/Al2O3 catalyzed propane dehydrogenation

Precise control of porous alumina microstructures is always challenging due to the diversity and complexity of the growth process-related alumina crystalline phase and surface properties. In this work, we established a bottom-up synthesis route with a combination of rapid precipitation at high supersaturation and high-temperature aging in terms of enhancing particle aggregation kinetics. Surprisingly, we discovered that there were two distinct growth stages of alumina precursor (ammonium aluminum carbonate hydroxide) during the aging procedure, that is, oriented attachment at the early stage of crystallization and subsequent Oswald ripening. High-temperature aging can effectively strengthen the aggregation kinetics between the particles and produce large mesoporous (∼16 nm) and a remarkable number of defect sites with the exposure of up to 14 % unsaturated pentacoordinate aluminum ions. Owing to the presence of strong metal-support interactions, the alumina-supported PtSn catalyst exhibited excellent catalytic activity in the propane dehydrogenation reaction with propylene formation with 99 % selectivity and superior stability with a low deactivation rate of 0.007 h−1 over 24 h. These results suggested that it was feasible and instructive to achieve precise control of the structure and surface properties of alumina by manipulating the aggregation process of the initial particles during the aging stage.

Dual-Atom Catalyst with N-Colligated Zn1Co1 Species as Dominant Active Sites for Propane Dehydrogenation.

Dual-atom catalysts (DACs) with paired active sites can provide unique intrinsic properties for heterogeneous catalysis, but the synergy of the active centers remains to be elucidated. Here, we develop a high-performance DAC with Zn1Co1 species anchored on nitrogen-doped carbon (Zn1Co1/NC) as the dominant active site for the propane dehydrogenation (PDH) reaction. It exhibits several times higher turnover frequency (TOF) of C3H8 conversion and enhanced C3H6 selectivity compared to Zn1/NC or Co1/NC with only a single-atom site. Various experimental and theoretical studies suggest that the enhanced PDH performance stems from the promoted activation of the C-H bond of C3H8 triggered by the electronic interaction between Zn1 and Co1 colligated by N species. Moreover, the dynamic sinking of the Zn1 site and rising of the Co1 site, together with the steric effect of the dissociated H species at the bridged N during the PDH reaction, provides a feasible channel for C3H6 desorption through the more exposed Co1 site, thereby boosting the selectivity. This work provides a promising strategy for designing robust hetero DACs to simultaneously increase activity and selectivity in the PDH reaction.

Amorphous CeOx Islands on Dealuminated Zeolite Beta to Stabilize Pt Nanoparticles as Efficient and Antisintering Catalysts for Propane Dehydrogenation.

Pt-based catalysts have been widely used in propane dehydrogenation due to their superior activation of C-H bonds and weak scission of C-C bonds. However, in the process of repeated calcination to remove deposited coke, the active Pt species tend to sinter, resulting in a significant decline in catalytic activity. In this study, amorphous CeOx islands loaded on dealuminated Beta zeolite were prepared via simple wetness impregnation. Then, partially embedded Pt nanoparticles in CeOx islands were obtained after reduction owing to the affinity of CeOx for Pt. In the propane dehydrogenation reaction, Pt/Ce5-SiBeta with a Ce loading of 4.55 wt % and Pt loading of 0.72 wt % exhibited the highest activity and the lowest inactivation constant at 550 °C. More importantly, due to the anchoring effect of CeOx on Pt, the catalytic activity of Pt could be recovered after a simple calcination-reduction regeneration process, avoiding the chlorination treatment for the redispersion of Pt species used in industry. In addition, to improve the selectivity of the Pt/Ce5-SiBeta catalyst, a PtSn/Ce5-SiBeta catalyst with excellent activity, selectivity, and recycling stability has been prepared by introducing Sn into Pt/Ce5-SiBeta. The use of amorphous CeOx islands to improve the sintering resistance of Pt opens up new prospects for the design of stable industrial dehydrogenation catalysts.

Identifying the active site and structure–activity relationship in propane dehydrogenation over Ga2O3/ZrO2 catalysts

ZrO2-based catalysts have attracted extensive attention in propane dehydrogenation (PDH) owing to their environmental compatibility, low costs, and superior catalytic performance. However, the structure–activity relationship and mechanistic analysis of Ga2O3/ZrO2 in PDH are rarely studied where GaOx either acts as an active site or a promoter. Here, Ga2O3/ZrO2 catalysts with different Ga/Zr ratios were synthesized by the impregnation technique, and the structure–activity relationship was revealed by combining complementary in/ex-situ characterization methods with catalytic tests. It is found the rate of propene formation first increases linearly and then reaches a plateau with the increase of Ga2O3 loading, such activity-loading dependence is related to the evolution of Ga2O3 species varying from monodisperse to single-layer and then multilayer states. Activation energy and C3H8-TPSR results suggest the formation of a new active site with high intrinsic activity over Ga2O3/ZrO2. Furthermore, the molecular level reaction mechanism of Ga2O3/ZrO2 in PDH was studied by DFT calculations, which pointed out the active site structure was GaⅡ–O3cⅡ site exhibiting enhanced activation ability toward C–H bond and lower reaction barrier compared with bare ZrO2. This work is expected to offer new insights into understanding the structure–activity relationships over ZrO2-based catalysts for PDH reaction.

Effect of supports on the kind of in-situ formed ZnOx species and its consequence for non-oxidative propane dehydrogenation

Non-oxidative propane dehydrogenation (PDH) to propene is the basis of various large-scale processes suffering however from high costs or environmental incompatibility of currently applied Pt- or Cr-containing catalysts. Herein, we demonstrate that active and selective catalysts can be obtained from cheap and commercially available Zr- or Ti-based supports and ZnO without producing any liquid or solid waste. Catalytically active species formed in situ under PDH conditions are composed of isolated ZnOx as concluded from X-ray absorption spectroscopic analysis. The kind of support affects the geometry of such species that is probably decisive for catalyst activity. ZnOx on the surface of LaZrOx revealed the highest Zn-related TOF of propene formation. However, the following activity order in terms of space time yield of propene formation (STYC3H6) at 550 °C and about 50% equilibrium propane conversion using a feed with 40 vol% propane was obtained: ZnO//TiZrOx > ZnO//SiZrOx > ZnO//LaZrOx > ZnO//TiO2. The best-performing catalyst showed STYC3H6 of 2 kg kgcat−1 h−1 and was durable in 8 PDH/regeneration cycles. Temporal analysis of products with submillisecond resolution suggests that H2 formation should be the rate-determining step in the course of the PDH reaction.

Propane dehydrogenation over Pt and Ga-containing MFI zeolites with modified acidity and textural properties

A variety of oxides (titanium, tin, calcium, magnesium, and gallium) were supported over nano-crystalline ZSM-5 zeolite (n-ZSM-5) by wet impregnation, characterized and evaluated for propane dehydrogenation (PDH) reaction. To enhance the catalytic performance of the oxide-modified n-ZSM-5, Pt nanoparticles were also dispersed over the oxides-supported zeolite catalysts by wet impregnation. Finally, Ga-containing MFI zeolites were used as catalysts in the PDH. Ga was incorporated into the zeolite by two different methods, via hydrothermal synthesis and via wet impregnation. In the PDH reaction, Pt-containing samples exhibited a high initial catalytic activity although they suffered a fast deactivation by coke deposition. On the contrary, Ga-containing MFI catalysts showed a remarkable stability in the PDH reaction. In particular, the catalyst in which Ga was incorporated into the MFI structure by hydrothermal synthesis (Ga-MFI (nSH)) achieved the highest catalytic performance in PDH (9% conversion and 80% propylene selectivity) due to the synergy between the Brønsted and Lewis acid sites (BAS and LAS) and the optimal strength of its LAS sites. These results denote the great potential of Ga-MFI zeolites as catalysts in PDH reactions.