Search Results (43)

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 effects of Ce incorporation into trimetallic PtSnIn-supported catalysts were investigated for a propane dehydrogenation reaction with advanced characterization techniques. It was found that some Ce species exist in the form of CeAlO₃ on the reduced PtSnIn/xCe-Al catalyst, significantly enhancing the thermal stability of the alumina support. The NH₃-TPD measurements verified that the total acidity of the PtSnIn/xCe-Al catalysts decreases with the addition of Ce. The PtSnIn/1.5Ce-Al catalyst exhibits the optimal particle distribution with the smallest Pt particle size of 8.0 nm, which was revealed by TEM. The H₂-TPR and XPS results suggest that more oxidized-state Sn species form on catalyst surfaces, and the metal–support interaction can be strengthened when Ce is introduced. Furthermore, TG analysis demonstrates that Ce incorporation substantially reduces coke formation on the spent catalysts. The PtSnIn/1.5Ce-Al catalyst exhibits exceptional catalytic performance, achieving an initial propane conversion of 62.6% and maintaining a conversion of 57.2% after a 120 min reaction. In addition, the PtSnIn/1.5Ce-Al catalyst possesses high long-term stability. Over 40.0% propane conversion can be maintained after a 53 h continuous PDH reaction. These findings highlight the pivotal role of Ce in improving the structural properties and catalytic performance of PtSnIn-based catalysts for propane dehydrogenation, offering valuable insights for the design of highly efficient and stable dehydrogenation catalysts. Full article

A series of 5 wt.% Cr/SiO₂ catalysts were prepared through incipient wet impregnation using different chromium salts as a source of Cr (chromium (III) sulfate, acetylacetonate, nitrate, ammonium dichromate). The obtained catalysts were characterized by SEM-EDX, TEM, DRIFT-CD₃CN spectroscopy, UV-VIS diffuse reflectance spectroscopy, and the N₂ low-temperature adsorption–desorption technique. The catalysts were tested in propane, and isobutane dehydrogenation assisted with CO₂ at 600–750 °C. The highest activity in propane dehydrogenation was observed for the catalyst obtained from chromium acetylacetonate, the yield of propylene was 32% at 750 °C, and in the isobutane dehydrogenation reaction, the catalyst obtained from chromium sulfate was the best one; the yield of isobutene was ~30% at 600 °C. The obtained results show that the type of chromium precursor has a significant effect on the efficiency of the catalyst in the propane and isobutane dehydrogenation with CO₂. Full article

A huge variety of chemical commodities are built from propylene molecules, and its conventional production technologies (naphtha steam cracking and fluid catalytic cracking) are unable to satisfy C₃H₆’s increasing requirements. In this scenario, Direct Propane Dehydrogenation (PDH) provides a practical and reliable route for supplying this short demand due to the economic availability of the raw material (C₃H₈) and the high propylene selectivities. The main challenges of propane dehydrogenation technology are related to the design of very active catalysts with negligible byproduct formation. In particular, the issue of catalyst deactivation by coke deposition still requires further development. In addition, PDH is a considerable endothermic reaction, and the efficiency of this technology is strictly related to heat transfer management. Thus, this current review specifically discusses the recent advances in highly dispersed bimetallic and trimetallic catalysts proposed for the PDH reaction in both conventional-heated and microwave-heated reactors. From the point of view of catalyst development, the recent research is mainly addressed to obtain nanometric and single-atom catalysts and core–shell alloys: atomically dispersed metal atoms promote the desorption of surface-bonded propylene and inhibit its further dehydrogenation. The discussion is focused on the alternative formulations proposed in the last few years, employing active species and supports different from the classical Pt-Sn/Al₂O₃ catalyst. Concerning the conventional route of energy-supply to the catalytic bed, the advantage of using a membrane as well as fluidized bed reactors is highlighted. Recent developments in alternative microwave-assisted dehydrogenation (PDH) employing innovative catalytic systems based on silicon carbide (SiC) facilitate selective heating of the catalyst. This advancement leads to improved catalytic activity and propylene selectivity while effectively reducing coke formation. Additionally, it promotes environmental sustainability in the ongoing electrification of chemical processes. 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

The robust electronegativity of the [BO₃]³⁻ structure enables the extraction of electrons from adjacent metals, offering a strategy for modulating oxygen activation in propane oxidative dehydrogenation. Metals (Ni 1.91, Al 1.5, and Ca 1.0) with varying electronegativities were employed to engineer borate catalysts. Metals in borate lacked intrinsic catalytic activity for propane conversion; instead, they modulated [BO₃]³⁻ group reactivity through adjustments in electron density. Moderate metal electronegativity favored propane oxidative dehydrogenation to propylene, whereas excessively low electronegativity led to propane overoxidation to carbon dioxide. Aluminum, with moderate electronegativity, demonstrated optimal performance. Catalyst AlBOx-1000 achieved a propane conversion of 47.5%, with the highest propylene yield of 30.89% at 550 °C, and a total olefin yield of 51.51% with a 58.92% propane conversion at 575 °C. Furthermore, the stable borate structure prevents boron element loss in harsh conditions and holds promise for industrial-scale catalysis. 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

Compared to the currently widely used propane dehydrogenation process for propylene production, propane oxidative dehydrogenation (ODHP) offers the advantage of no thermodynamic limitations and lower energy consumption. However, a major challenge in ODHP is the occurrence of undesired over-oxidation reactions of propylene, which reduce selectivity and hinder industrialization. MOFs possess a large number of metal sites that can serve as catalytic centers, which facilitates the easier access of reactants to the catalytic centers for reaction. Additionally, their flexible framework structure allows for easier adjustment of their pores compared to metal oxides and molecular sieves, which is advantageous for the diffusion of products within the framework. This property reduces the likelihood of prolonged contact between the generated propylene and the catalytic centers, thus minimizing the possibility of over-oxidation. The research on MOF catalyzed oxidative dehydrogenation of propane (ODHP) mainly focuses on the catalytic properties of MOFs with cobalt oxygen sites and boron oxygen sites. The advantages of cobalt oxygen site MOFs include significantly reduced energy consumption, enabling catalytic reactions at temperatures of 230 °C and below, while boron oxygen site MOFs exhibit high conversion rates and selectivity, albeit requiring higher temperatures. The explicit structure of MOFs facilitates the mechanistic study of these sites, enabling further optimization of catalysts. This paper provides an overview of the recent progress in utilizing MOFs as catalysts for ODHP and explores how they promote progress in ODHP catalysis. Finally, the challenges and future prospects of MOFs in the field of ODHP reactions are discussed. 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

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 ZnN_x 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. 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