Search Results (21)

This review examines the state-of-the-art in catalytic oxidative dehydrogenation of propane and butane to olefins under oxygen-free gas-phase conditions (FOx–PCODH and FOx–BCODH). First, it is compared with traditional methods for C₃–C₄ olefin production, using reaction enthalpies as an indicator of the process energy required. The role of catalyst oxygen species, including lattice and chemisorbed oxygen, is discussed in relation to olefin formation under oxygen-free gas-phase operation. This is followed by a review of V₂O₅-based catalysts, with particular emphasis on co-catalysts and catalyst supports. The performance of V₂O₅-based catalysts for FOx–PCODH is assessed using overall olefin formation rates. Special attention is given to catalyst performance in the mini-fluidized CREC Riser Simulator, which exhibit the highest overall olefin formation rates. These studies are also valuable to shed light into the FOx–PCODH reaction mechanism and to determine paraffin conversion, olefin selectivity, oxygen availability, and coke formation. This data can be used to determine FOx–PCODH kinetic parameters by assessing the effects of temperature, contact time, paraffin partial pressure, and catalyst-to-feedstock ratio. Finally, this review analyzes Barracuda-based numerical simulations of a large-scale downer reactor using statistically derived kinetic parameters. These simulations are employed to confirm the viability of the FOx–PCODH process at an industrial scale. Full article

The Temporal Analysis of Products (TAP) pulse response technique provides valuable insights into catalytic function and reaction kinetics. However, complex fragmentation patterns in the TAP mass spectrometry signals can complicate precise quantification, particularly when analyzing transient gas flux data typical of TAP experiments. This work demonstrates a standard defragmentation method that deconvolves transient TAP signals while maintaining the temporal resolution of the experiment. First, the integrals of calibration gas fluxes are used to determine the fingerprint fragmentation pattern and construct a fragmentation matrix. This matrix is then used to defragment experimental flux data at each recorded time point via a non-negative least squares regression. The effectiveness of this method is demonstrated using virtual data and control experiments with a TAP reactor system. The defragmentation is then applied to the more complex propane dehydrogenation reaction on a chromia/alumina catalyst, which can contain up to ten significant gas species in the reactor outlet. Initial propane pulsing reveals an induction period during which propane is fully oxidized to CO_2, followed by partial reduction to CO. Afterwards, there is a transition in chemistries towards coking and propylene production. Our example illustrates a practical method for the accurate determination of the time-dependent reactant/product concentrations and rates for a thorough analysis of the propane dehydrogenation kinetics. This approach can be broadly applied to any transient mass spectrometry experiment for a better understanding of catalyst-reaction dynamics. Full article

This study reports on the performance of alumina-supported copper-based catalysts in the oxidative dehydrogenation of propane, with copper dispersed on two distinct commercial aluminium oxide supports made of micro- and nanosized alumina, respectively. The activity and selectivity of the two catalysts was investigated at temperatures between 250 and 550 °C. At a propane-to-O₂ ratio of 1:1, Cu/nanoAl₂O₃ achieves propylene selectivity of 35–48% at low temperatures (250–300 °C), while Cu/Al₂O₃ only exhibits activity starting at 350 °C with about 40% propylene selectivity. Altering the propylene-to-oxygen ratio to 3:1 enhances selectivity towards propylene in both catalysts, up to about 64% on Cu/Al₂O₃ at temperatures of 250–350 °C. The switch to the mild oxidant CO₂ boosts propylene selectivity to 100%. In case of Cu/nanoAl₂O₃, the rate of propylene formation doubles that of the obtained with O₂ used as oxidant. While with CO₂ the Cu/nanoAl₂O₃ catalyst retains 100% propylene selectivity up to 500 °C, on the less active Cu/Al₂O₃ cracking sets off already at 400 °C. The different size of copper particles in the two catalysts is seen as a primary factor determining the observed differences in the performance of the studied catalysts. Full article

Propylene (C₃H₆) is a vital building block in the chemical industry as it serves as a key raw material for producing plastics, synthetic fibers and numerous daily-use chemicals. However, the current production routes of C₃H₆ are energy-intensive and face sustainability challenges, prompting the scientific community to explore alternative technologies for its production. The oxidative dehydrogenation of propane (ODHP) using CO₂ as a soft oxidant offers a safe and sustainable pathway for C₃H₆ production, where CO₂ can act as a hydrogen scavenger, coke suppressor and site re-activator. Gallium- and chromium-based catalysts are among the most studied systems for CO₂-assisted ODHP, yet they operate by distinct mechanisms: Ga catalysts follow pathways where both acidic and basic sites are involved, while Cr catalysts rely on redox cycles involving variations in the oxidation state of chromium. In addition to performance and reaction mechanism, Ga- and Cr-based catalysts differ markedly in terms of sustainability, with Cr systems facing environmental and regulatory challenges associated with Cr⁶⁺ species toxicity, while Ga systems, although less toxic, are constrained by gallium scarcity and cost. This review compares Ga- and Cr-based catalysts side by side, emphasizing how support effects, addition of promoters and mechanistic insights fine tune their performance. The aim is to highlight the advantages, the limitations as well as the sustainability implications of these materials and finally to outline future directions for designing more efficient and environmentally friendly catalysts for propylene production. Full article

Propylene production through the CO₂-assisted oxidative dehydrogenation of propane (CO₂-ODP) is an effective route able to address the ever-increasing demand for propylene and simultaneously utilize CO₂. In this study, a series of alumina-supported gallium oxide catalysts of variable Ga₂O₃ loading was synthesized, characterized, and evaluated with respect to their activity for the CO₂-ODP reaction. It was found that both the catalysts’ physicochemical characteristics and performance were strongly affected by the amount of Ga₂O₃ dispersed on Al₂O₃. Surface basicity was maximized for the sample containing 20 wt.% Ga₂O₃, whereas surface acidity was monotonically increased with increasing Ga₂O₃ loading. A volcano-type correlation was found between catalytic performance and acid/base properties, according to which propane conversion and propylene yield exhibited optimum values for intermediate surface basicity and acidity, which both correspond to the sample containing 30 wt.% Ga₂O₃. The dispersion of a suitable amount of Ga₂O₃ on the Al₂O₃ surface not only enhances the conversion of propane to propylene but also suppresses the formation of side products (C₂H₄, CH₄, and C₂H₆) at temperatures of practical interest. The 30%Ga₂O₃-Al₂O₃ catalyst exhibited very good stability at 550 °C, where byproduct formation and carbon deposition were limited. Mechanistic studies indicated that the reaction proceeds through a two-step oxidative route with the participation of CO₂ in the abstraction of H₂, originating from propane dehydrogenation, through the reverse water–gas reaction (RWGS) reaction, shifting the thermodynamic equilibrium towards propylene generation. Full article

The oxidative dehydrogenation of propane with CO₂ (CO₂-ODP) was investigated over different metal oxides M_xO_y (M: Ca, Sn, Cr, Ga) supported on a SiO₂ surface. Catalysts were characterized employing nitrogen adsorption/desorption, X-ray diffraction (XRD), CO₂ temperature programmed desorption (CO₂-TPD) and pyridine adsorption/desorption experiments in order to identify their physicochemical properties and correlate them with their activity and selectivity for the CO₂-ODP reaction. The effect of operating reaction conditions on catalytic performance was also examined, aiming to improve the propylene yield and suppress side reactions. Surface acidity and basicity were found to be affected by the nature of M_xO_y, which in turn affected the conversion of propane to propylene, which was in all cases higher compared to that of bare SiO₂. Propane conversion, reaction rate and selectivities towards propylene and carbon monoxide were maximized for the Ga- and Cr-containing catalysts characterized by moderate surface basicity, which were also able to limit the undesired reactions leading to ethylene and methane byproducts. High surface acidity was found to be beneficial for the CO₂-ODP reaction, which, however, should not be excessive to ensure high catalytic activity. The silica-supported Ga₂O₃ catalyst exhibited sufficient stability with time and better than that of the most active Cr₂O₃-SiO₂ catalyst. Decreasing the weight gas hourly space velocity resulted in a significant improvement in both propane conversion and propylene yield as well as a suppression of undesired product formation. Increasing CO₂ concentration in the feed did not practically affect propane conversion, while led to a decrease in propylene yield. The ratio of propylene to ethylene selectivity was optimized for CO₂:C₃H₈ = 5:1 and space velocity of 6000 mL g⁻¹ h⁻¹, most possibly due to facilitation of the C–H bond cleavage against that of the C–C bond. Results of the present study provided evidence that the efficient conversion of propane to propylene is feasible over silica-based composite metal oxides, provided that catalyst characteristics have been optimized and reaction conditions have been properly selected. Full article

In the propane dehydrogenation process, the structure and catalytic performance stability of the catalyst are determined by its regeneration process, which includes oxidation of coke and oxychlorination to redisperse the supported metal particles. A commercial Pt-Sn catalyst was used in this work to investigate the impact of oxidation temperature on oxychlorination performance. The catalysts after oxidation and oxychlorination were characterized by H₂-TPR, CO-DRIFTS, HAADF-STEM, XPS, and CO chemisorption. It was found that mild sintering of Pt occurred during oxidation in the temperature range of 550–650 °C, and the catalyst could be fully restored in the subsequent oxychlorination treatment. Upon oxidation of the catalyst at 700 °C, a severe aggregation of Pt and SnOx could be observed, and the catalyst could not be fully regenerated under the given oxychlorination conditions. However, PDH catalyst deactivation caused by sintering is not irreversible. By tailoring the oxychlorination conditions, the detrimental effect of high oxidation temperature on regeneration could be ruled out. During the oxidation and oxychlorination treatment, the metal tends to migrate to anchor on sites with stronger metal–support interaction, which was helpful for enhancing the catalytic activity. Full article

CO₂ oxidative dehydrogenation of propane (CO₂-ODHP), being not only favorable for olefin production but also beneficial for CO₂ emission control, has recently attracted great attention. Here, a series of single metal (Cr) and bimetal (Zr, La, Fe) modified ZSM-5 zeolites were prepared via an impregnation method. It was found that the bimetal modified ZSM-5 possessed much higher C₃H₈ and CO₂ conversion than that of monometallic modified Cr_3%-ZSM-5 (Cr_3%-Z5), especially for Cr_3%Zr_2%-ZSM-5 (Cr_3%Zr_2%-Z5), which displayed the highest activity (65.4%) and olefin yield (1.65 × 10³ μmol·$g_{cat}^{-1}$ h⁻¹). Various characterizations were performed, including XRD, N₂ adsorption-desorption, H₂-TPR, Raman, XPS, HAAD-STEM, and TEM. It was revealed that Zr not only favored an improvement in the redox ability of Cr, but also contributed to the surface dispersion of loaded Cr species, constituting two major reasons explaining the superior activity of Cr_3%Zr_2%-Z5. To further improve CO₂-ODHP catalytic behavior, a series of Cr_3%-ZSM-5@SBA-15-n composite zeolite catalysts with diverse (ZSM-5/SBA-15) mass ratios were prepared (Cr_3%-ZS-n, n = 0.5, 2, 6, 16), which screened out an optimum mass ratio of six. Based on this, the Cr_3%Zr_2%-ZS-6 compound was further prepared, and it eventually achieved even higher CO₂-ODHP activity (76.9%) and olefin yield (1.72 × 10³ μmol·$g_{cat}^{-1}$ h⁻¹). Finally, the CO₂-ODHP reaction mechanism was further investigated using in situ FTIR, and it was found that the reaction followed the Mars–van Krevelen mechanism, wherein CO₂ participated in the reaction through generation of polydentate carbonates. The Cr⁶⁺ constituted as the active site, which was reduced to Cr³⁺ after the dihydrogen reaction, and was then further oxidized into Cr⁶⁺ by CO₂, forming polydentate carbonates, and thus cycling the reactive species Cr⁶⁺. Additionally, assisted by a Brönsted acid site (favoring breaking of the C-C bond), C₂H₄ and CH₄ were produced. Full article

The structure and performance stability of a Pt-based catalyst for propane dehydrogenation during its reaction–regeneration cycles is one of the key factors for its commercial application. A 0.3% Pt/Al₂O₃ catalyst with a sub-nanometric particle size was prepared and two different types of regeneration processes, long-term dichloroethane oxychlorination and a reaction–oxidation–oxychlorination cycle, were investigated on this catalyst. The fresh, sintered and regenerated catalyst was characterized by HAADF-STEM, CO-DRIFTS, XPS, CO chemisorption and N₂ physisorption, and its catalytic performance for propane dehydrogenation was also tested. The results show that the catalysts tend to have a similar particle size, coordination environment and catalytic performance with the extension of the regeneration time or an increase in the number of cycles in the two regeneration processes, and a common steady state could be achieved on the catalysts. This indicates that structure of the catalyst tends to approach its equilibrium state in the regeneration process, during which the utilization efficiency of Pt is maximized by increasing the dispersion of Pt and its intrinsic activity, and the structural robustness is secured. The performance of the catalyst is comparable to that of a single-atom Pt/Al₂O₃ catalyst. Full article

The CO₂-assisted oxidative dehydrogenation of propane (ODP) was investigated over titania based composite metal oxides, 10% M_xO_y-TiO₂ (M: Zr, Ce, Ca, Cr, Ga). It was found that the surface basicity of composite metal oxides was significantly higher than that of bare TiO₂ and varied in a manner which depended strongly on the nature of the M_xO_y modifier. The addition of metal oxides on the TiO₂ surface resulted in a significant improvement of catalytic performance induced by a synergetic interaction between M_xO_y and TiO₂ support. Propane conversion and propylene yield were strongly influenced by the nature of the metal oxide additive and were found to be superior for the Cr₂O₃-TiO₂ and Ga₂O₃-TiO₂ catalysts characterized by moderate basicity. The reducibility of the latter catalysts was significantly increased, contributing to the improved catalytic performance. This was also the case for the surface acidity of Ga₂O₃-TiO₂ which was found to be higher compared with Cr₂O₃-TiO₂ and TiO₂. A general trend was observed whereby catalytic performance increased significantly with decreasing the primary crystallite size of TiO₂. DRIFTS studies conducted under reaction conditions showed that the adsorption/activation of CO₂ was favored on the surface of composite metal oxides. This may be induced by the improved surface basicity observed with the M_xO_y addition on the TiO₂ surface. The Ga₂O₃ containing sample exhibited sufficient stability for about 30 h on stream, indicating that it is suitable for the production of propylene through ODP with CO₂ reaction. Full article

Non-oxidative propane dehydrogenation (PDH) is becoming an increasingly important approach to propylene production, while cobalt-containing catalysts have recently demonstrated great potential for use in this reaction, providing efficiencies comparable to those of industrially employed Pt- and Cr-based catalytic systems. It is therefore essential to clarify the nature of their active sites, especially since contradictory opinions on this issue are expressed in the literature. In this study, efforts were made to determine the state of Co in cobalt aluminates (CoAl₂O₄-Al₂O₃) responsible for PDH under typical operating conditions (600 °C, 1 atm). It is shown that the catalyst with a low cobalt content (Co/Al = 0.1) ensured the highest selectivity to propylene, ca. 95%, while maintaining significant propylene conversion. The structural motifs such as cobalt oxide and metallic cobalt nanoparticles, in addition to tetrahedral Co²⁺ species in the CoAl₂O₄ spinel system, were evaluated as potential active-site ensembles based on the obtained catalytic performance data in combination with the XRD, H₂-TPR, TEM and XPS characteristics of as-synthesized, spent and spent–regenerated catalysts. It is revealed that the most likely catalytic sites linked to PDH are the Co-oxide forms tightly covering alumina or embedded in the spinel structure. However, additional in situ tuning is certainly needed, probably through the formation of surface oxygen vacancies rather than through a deeper reduction in Co⁰ as previously thought. Full article

Propylene is an important raw material for the production of many valuable compounds, especially polypropylene, the consumption of which continues to grow every year. The reaction of oxidative dehydrogenation of propane, where carbon dioxide is used as a mild oxidant, is a promising method for producing propylene. At the same time, the problem of utilization of greenhouse gas CO₂ is partially solved. The synthesis and analysis of the physicochemical properties of mesoporous silicate MCM-41 and supported catalysts CrO_x/MCM-41 prepared on its basis were carried out. These catalysts were prepared using incipient wetness impregnation. The support and catalysts were characterized by the methods of low-temperature nitrogen adsorption, TG-DTA, XRD, SEM, TPR-H₂, UV/Vis diffuse reflectance spectroscopy, and small-angle X-ray scattering. It is shown that chromium is present in the samples simultaneously in the form of Cr³⁺ and Cr⁶⁺. The catalytic tests were performed in the range of 550–700 °C. The highest selectivity for propylene was observed for the 5%Cr/MCM-41 catalyst and was 76% at a temperature of 650 °C with a propane conversion of 20%. The deposited catalysts Cr/MCM-41 and Cr/SiO₂ (Acros) were compared. The propylene selectivity for the MCM-41-supported catalyst was ~1.5 times higher than that for the SiO₂-supported catalyst. Full article

Carbon dioxide (CO₂) assisted oxidative dehydrogenation of propane over Ga-modified catalysts is highly sensitive to the identity of support, but the underlying cause of support effects has not been well established. In this article, SSZ-13, SSZ-39, ZSM-5, silica and γ-Al₂O₃ were used to load Ga species by incipient wet impregnation. The structure, textural properties, acidity of the Ga-based catalysts and the process of CO₂-assisted oxidative dehydrogenation of propane were examined by X-ray diffraction (XRD), nitrogen physisorption (N₂ physisorption), ammonia temperature-programmed desorption (NH₃-TPD), pyridine chemisorbed Fourier transform infrared spectra (Py-FTIR), OH-FTIR and in situ FTIR. Evaluation of the catalytic performance combined with detailed catalyst characterization suggests that their dehydrogenation activity is positively associated with the number of acid sites in middle strength, confirming that the Lewis acid sites generated by Ga cations are the active species in the reaction. Ga/Na-SSZ-39(9) also has feasible acidic strength and a unique channel structure, which is conducive to the dissociative adsorption of propane and desorption of olefins. The Ga/Na-SSZ-39(9) catalysts showed superior olefins selectivity and catalytic stability at 600 ℃ compared to any other catalysts. This approach to quantifying support acid strength, and channel structure and applying it as a key catalytic descriptor of support effects is a useful tool to enable the rational design of next-generation CO₂-assisted oxidative dehydrogenation catalysts. Full article

The oxidative dehydrogenation of alkanes is a prospective method for olefins production. CO₂-assisted propane dehydrogenation over metal oxide catalysts provides an opportunity to increase propylene production with collateral CO₂ utilization. We prepared the chromia catalysts on various mesoporous aluminosilicate supports, such as halloysite nanotubes, nanostructured core/shell composites of MCM-41/halloysite (halloysite nanotubes for the core; silica of MCM-41-type for the shell), and MCM-41@halloysite (silica of MCM-41-type for the core; halloysite nanotubes for the shell). The catalysts have been characterized by X-ray fluorescence analysis, low-temperature nitrogen adsorption, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption of ammonia, transmission electron microscopy with energy-dispersive X-ray spectroscopy, and thermogravimetric analysis. The catalysts’ performance in carbon-dioxide-assisted propane dehydrogenation has been estimated in a fixed-bed reactor at atmospheric pressure. The most stable catalyst is Cr/halloysite, having the lowest activity and the largest pore diameter. The catalyst, Cr/MCM-41/HNT, shows the best catalytic performance: having the highest conversion (19–88%), selectivity (83–30%), and space–time yield (4.3–7.1 mol C₃H₆/kg catalyst/h) at the temperature range of 550–700 °C. The highest space–time yield could be related to the uniform distribution of the chromia particles over the large surface area and narrow pore size distribution of 2–4 nm provided by the MCM-41-type silica and transport channels of 12–15 nm from the halloysite nanotubes. Full article

Three series of zeolite catalysts Co all-silica and Co Al-containing zeolites beta were prepared for use in the selective oxidative dehydrogenation of propane to propylene. Two series of zeolite catalysts Co all-silica were prepared by a two-step postsynthesis method at pH = 2.5 and pH = 3.0–9.0, respectively, which allows the incorporation of cobalt into SiBEA zeolite in the form of isolated framework pseudo-tetrahedral Co(II) species. The incorporation of Co ions into vacant T-atom sites and their reaction with silanol groups were demonstrated by NMR and FTIR methods. The generation of Lewis acid sites without the formation of Brønsted sites was proved by FTIR using pyridine and CO as probe molecules. The state of cobalt in three series of prepared and calcined zeolite catalysts was characterized by DR UV-vis. This technique allowed to show that for low Co content (<2 wt.%) cobalt is present in the form of framework pseudo-tetrahedral Co(II) species. For higher Co content (>2 wt.%), both framework pseudo-tetrahedral and extra-framework octahedral Co(II) species are present. The Co Al-containing zeolite beta series prepared on non-dealuminated support shows the presence of extra-framework octahedral Co(II) only. Full article