Performance In Dehydrogenation Of Propane Research Articles

Stabilizing ultra-small bimetallic PtSn clusters within S-1 crystals for effective propane dehydrogenation with low Pt loading

It’s a great challenge for enhancing the stability over Pt-based catalysts with low Pt loading during propane dehydrogenation based upon the manipulation of ultra-small PtSn clusters and their compositions. Here, we developed a novel strategy to produce and stabilize sub-nanometer PtSn clusters even atomical dispersion within Silicalite-1 crystals via tailoring calcination atmosphere from air to argon, which could achieve a stable performance of propane dehydrogenation with only 0.15 wt% Pt loading. Argon calcination atmosphere of PtSn@Silicalite-1 significantly decreased the size of PtSn clusters, which further presented a strikingly catalytic performance with the high formation of propylene over 8.0 mol[C3H6]·g[Pt]−1·h−1 even after 3840 min at 600 °C (WHSV=760 g[C3H8]·g[Pt]−1·h−1). Hardly any deactivation was obtained over PtSn8@S-1-Ar-50 after long-term runs for 3840 min with an extremely low deactivation constant of 0.0001 h−1 so far, which was mainly derived from the outstanding stability of PtSn sub-nanometers within S-1 crystals through appropriate flow rate of argon calcination atmosphere.

Impact of various metal promoters on the propane dehydrogenation performance of cobalt-based catalysts

Large-scale exploitation of natural gas and shale gas has spurred the development of the propane dehydrogenation technology. While cobalt-based catalysts, known for their low cost and low toxicity, effectively activate C–H bonds, they are often deactivated because of coke formation. In this study, we prepared SBA-15 molecular sieves using a hydrothermal synthesis method and developed a series of Co-based catalysts supported on SBA-15 with various metal promoters (denoted Co-X/SBA-15, where X = Mn, Fe, Mg, Zn, or La) via an incipient wetness impregnation method. Characterization techniques and activity evaluation results revealed that the Co–O–Mg structure in the Co-Mg/SBA-15 catalyst stabilizes the primary Co2+ active site and hinders the reduction of the CoOx species. The incorporation of Mg enhances the total alkalinity of the catalyst, facilitating propane adsorption and propylene desorption, leading to superior activity and stability. Although the addition of La improved propylene selectivity, it did not significantly enhance propane conversion. Conversely, the introduction of Mn, Fe, and Zn into the catalyst inhibited the reaction.

Suppressed Active Site Loss by Y-Doped ZnO/Silicalite-1 for Superior CO2 Oxidative Propane Dehydrogenation Performance by Microwave Catalysis

Suppressed Active Site Loss by Y-Doped ZnO/Silicalite-1 for Superior CO₂ Oxidative Propane Dehydrogenation Performance by Microwave Catalysis

Promoting propane dehydrogenation performance of Co/silicalite-1 catalysts

Co catalysts supported on silicalite-1 (S-1) zeolite are developed in this work for direct propane dehydrogenation to propylene (PDH), showing excellent activity and propylene selectivity. Comprehensive characterizations of XRD, SEM, N2-sorption, TEM, DR UV–vis, H2-TPR, and TGA jointly evidence that the atomic-level dispersed CoOx species have significantly positive influence on the catalytic performance for PDH reaction. Alkaline treatment is a kind of advanced and effective method to create a number of defects on S-1 support, further isolating CoOx species and thus depressing side reactions. After the optimizing treatment on support, the catalyst with 0.5 wt% of Co supported on the S-1 pretreated with 0.1 mol/L of NaOH solution can exhibit simultaneously 78 % of propane conversion and 97 % of propylene selectivity after 15-minute of induction period. This work confirms that the highly-dispersed CoOx species bonded to zeolite are necessary for obtaining highly active and selective Co sites confined in the developed oxygen defects for the PDH reaction possibly due to the interface-induced effect between Co-O, and the main deactivation cause is ascribed to the migration and aggregation of Co sites in defects which points out that the direction for developing commercial Co based catalysts should focus on the stability design of active single Co atoms.

The Acid Roles of PtSn@Al2O3 in the Synthesis and Performance of Propane Dehydrogenation.

In this study, a PtSn/Al2O3 catalyst with bimetallic uniform distribution in the sphere was synthesized. The PDH performance and characterization analyses, such as with FTIR, XPS, and NH3-TPD, were investigated. The effects of acid on the PDH performance were analyzed. Citric acid (CA) acted as a competing adsorbent in the preparation process of the PtSn/Al2O3 catalyst to synthesize the uniform catalyst. Water washing and alkali-treated samples were also studied. SEM line scanning revealed that increased the apparent concentration of Pt metal from 0.23 to 0.30 with citric acid. In contrast to the fresh PtSn/Al2O3 catalyst, the addition of citric acid increased the PDH selectivity from 74% to 93%. After alkali or water washing treatments, the catalyst's selectivity further increased to 96%. Strong acid sites promoted the breaking of C-C bonds during the PDH reaction, resulting in more methane and ethylene byproducts, and decreased catalyst selectivity for fresh PtSn/Al2O3. From the PDH reaction thermodynamic analysis, a relatively sub-atmospheric pressure environment with a lower propane pressure could be the reasonable choice.

Origin of extra-stable multinuclear zinc species riveted into siliceous zeolite for efficient propane dehydrogenation

Zn-based catalysts are promising for direct propane dehydrogenation (PDH) to propylene owing to their cheaper and environment-friendly features but are subjected to serious depletion of active Zn component under working conditions. Herein, we successfully open a “black box” for the origin of active Zn speciations confined within the silicalite-1 (S-1) zeolite by thermogravimetric-mass spectrometry analysis and in-situ Fourier transform infrared spectroscopy. Guided by this, single-site, multinuclear and nanometer hydroxylated ZnOx species are separately encapsulated into the channels of S-1 zeolite by the controllable transformation of intermediate Zn(OH)x with assistant of vicinal- and nest-silanols. Delightfully, synthetic m-ZnOx@S-1 catalyst enables enviable propylene formation rate (50.8 mmol∙gcat−1∙h−1) and propylene selectivity (>96 %) in the PDH reaction. Most importantly, initial activity revives as before and without Zn loss after 7 regeneration cycles. This exceptional PDH performance is benefited from low-coordination and extra-stable multinuclear ZnOx species that can greatly lower the dehydrogenation barrier, favoring the PDH pathway to further produce propylene and hydrogen. These findings elucidate the potential of Zn-based zeolite catalysts for the development of PDH reaction and afford value-filled opportunities in alternative PDH catalyst optimization.

Propane dehydrogenation performance of titanosilicate-1 supported CoOx catalysts by adjusting the acidity and reducibility

The development of low-cost and toxicity-free cobalt oxide-based catalysts for propane dehydrogenation to propylene (PDH) has gained momentum. In this paper, titanosilicate-1 (TS-1) supported CoOx catalysts doped with different alkali and alkaline earth metal ions (M = Na, K, Mg, Ca and Ba) were prepared by adjusting the acidity, reducibility and oxidation state to increase the activity and stability during the PDH reaction. It was found that the decrease in the number of Lewis acid sites and lack of Co2+Ox species with the addition of K ions led to an almost complete loss of the activity of the Co-K catalyst. However, Co-Ca catalyst exhibited moderate acidity, more Lewis acid sites, a larger amount of the in-situ formed highly-dispersed metallic Co0 nanoparticles (∼5 nm) and Co2+Ox species strongly interacting with the support, all of which were responsible for its highest space-time yield (STY) of propylene formation (0.88 kg h−1 kgcat.−1). Though Co3O4 particles were more active for the side reactions, they could be readily reduced to metallic Co0 nanoparticles during the PDH process, and increased the selectivity to propylene with time on stream. Specifically, it was demonstrated that the highly-dispersed metallic Co0 nanoparticles were also active for the PDH activity, but was lower than Co2+Ox species that were strongly interacted with TS-1 support. The deposited coke on the catalysts was related to the catalyst deactivation. The Co0 species could not completely return to the oxidation states after burning off the deposited coke, which seemed to be related to the incomplete recovery of catalytic activity after regeneration.

Titanosilicate-1 Supported ZnO Catalysts for Steady Propane Dehydrogenation Performance

Titanosilicate-1 Supported ZnO Catalysts for Steady Propane Dehydrogenation Performance

PH-dependent growth of alumina nanorods with a high aspect ratio for enhanced propane dehydrogenation performance

Controllable synthesis of porous alumina is always challenging due to the diversity of precursors and the complexity of the growth process. In this work, alumina nanorods with adjustable aspect ratios were synthesized by precipitation to investigate the morphology evolution mechanism related to aging pH, and the structure–activity relationship of alumina. The evolution path of precursors ammonium aluminum carbonate hydroxide (NH4Al(OH)2CO3, AACH) was established by tracking the variation in electrical charges and nitrate concentration during the growth process. It was revealed that the anisotropic adsorption of ions on the AACH crystal facets can modulate the axial and radial growth rates of the microcrystalline rods, regulating the one-dimensional oriented assembly of AACH. Alumina synthesized at pH 9.5 exhibited more exposition of (100) facets due to its higher aspect ratio, resulting in an aluminum content of up to 30% in the five-coordinated state. Due to the presence of strong metal-support interactions, the corresponding PtSn/Al2O3 catalyst demonstrated good propane dehydrogenation activity and stability, with propylene formation with 99% selectivity within 30 h of reaction. This study highlighted the significance of pH regulation in the growth environment of AACH, enabling the selective exposure of crystal facets in the alumina support, and providing an effective pathway to obtain highly active and stable catalysts.

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 treated 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.

Boosting propane dehydrogenation performance over the highly dispersed Co(Ⅱ) sites on ultra-high silica ZSM-5 zeolite

Propane dehydrogenation (PDH) has emerged as an effective way to address the problem of propylene production gap in recent years. However, industrial catalysts are challenged by the scarcity of Pt and toxicity of CrOx. Herein, a series of Co-based catalysts supported on MFI type zeolites with various Si/Al ratios were synthesized by regulating the acid sites to alleviate side reactions. The catalyst Co/ZSM-5-1500 exhibits the superior PDH performance due to the highest proportion of Co(Ⅱ) active sites. The initial C3H6 formation rate is 6.5 mmol g−1cat h−1, along with good long-term stability across three cycles. The Brønsted acid sites over ZSM-5-40 are prone to catalyzing side reactions of cracking and coke deposition to decrease propylene selectivity and stability. This work demonstrates that Co species supported on high silica ZSM-5 zeolite via impregnation method is favorable to generate the highly dispersed Co(Ⅱ) species on the surface of zeolites, and the Co(Ⅱ) species are responsible for excellent PDH performance.

Structure Robustness of Highly Dispersed Pt/Al2O3 Catalyst for Propane Dehydrogenation during Oxychlorination Regeneration Process

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.

Structural dynamics of PtSn/SiO2 for propane dehydrogenation

Operando characterization reveals the structural dynamics of PtSn/SiO2 catalysts, hinting at a Pt-rich surface configuration for optimal propane dehydrogenation performance.

Dual Pt atoms stabilized by an optimized coordination environment for propane dehydrogenation

Tailoring atomically dispersed catalysts by various methods has been the subject of intense current research in heterogeneous catalysis. In this work, the structural stability and propane dehydrogenation performance of Pt-TiO2 catalysts with single, dual, and triple Pt atoms doped on the reduced TiO2 surface have been examined. Experimental results indicate the atomically dispersed Pt is thermally very stable and shows exceptionally high activity (TOFpropane = 4.93 s−1) and selectivity (∼98.5 %) for the dehydrogenation reaction. The recently developed machine-learning-based SSW-NN method is then employed to explore the global potential energy surface of the atomically dispersed Pt atom-doped TiO2, which suggests that the single and dual Pt atoms can be tightly held by the vacancies created on the reduced transition-metal oxide, as confirmed by DFT + U calculated energetics. After that, advanced characterization techniques are used in conjunction with microkinetic analysis to establish the quantitative structure–activity relationships. It is found that the dual-Pt-atom structure with two Pt atoms embedded in adjacent Ti and O vacancies is the only active ensemble that dramatically promotes the CH bond activation and hydrogen recombination, as compared to single Pt atoms accommodated by either Ti or O vacancies. These results provide new and direct evidence in support of the idea that specific function can be imparted to specific active sites by tuning their coordination environments, which makes it possible to tailor the catalytic properties of metal oxides to a particular reaction such as propane dehydrogenation.

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.

Modulating Propane Dehydrogenation Performance and Stability of Ni2P with Co Doping

Modulating Propane Dehydrogenation Performance and Stability of Ni2P with Co Doping

Influence of catalyst pelletization on propane dehydrogenation over hierarchical MFI zeolite supported with platinum-yttrium nanoparticles

Platinum-yttrium (PtY) nanoparticles supported on a siliceous form of mesoporous MFI zeolite (MZ) were recently found to exhibit excellent catalytic performance in propane dehydrogenation (PDH). Herein, potential shaping of the PtY/MZ catalyst is investigated from the laboratory-synthesized powder form into industrially preferable pellets. The MZ zeolite powder was synthesized using multi-ammonium surfactants as a structure-directing agent and then pelletized in a hydraulic press by itself or with inorganic binders (i.e., pseudoboehmite, fumed silica, or hydrotalcite). As a part of the sequential pelletization process, pressing was followed by a high-temperature treatment (923 K). Addition of 20 wt% pseudoboehmite resulted in the highest mechanical strength without a significant loss of the initial zeolite mesoporosity. The pseudoboehmite-bound pellet also showed high catalytic activity and longevity in PDH application when simultaneously impregnated with 1 wt% Pt [Pt(NH3)4(NO3)2] and 1 wt% Y [Y(NO3)2·6H2O]. Notwithstanding the observed high propane conversion, the pseudoboehmite-bound catalyst produced an unsatisfactory result of low propylene selectivity (∼60%). Image analyses of HAADF-STEM EDS and solid-state 31P NMR spectroscopic data suggest that such findings could be attributed to Al migration from pseudoboehmite onto zeolite regime during the phase transformation of pseudoboehmite in the shaping process. Alternatively, the uses of non-acidic binders, such as fumed silica and hydrotalcite binders were also demonstrated. The silica-bound catalyst yielded high propane conversion with high propylene selectivity although mechanical strengths of the pellet were compromised to a moderate level.

Promoting propane dehydrogenation over PtFe bimetallic catalysts by optimizing the state of Fe species

Optimizing the structure of Pt-based bimetallic catalysts is of utmost importance toward improving the propane dehydrogenation performance. It is challenging to precisely synthesize uniform PtFe alloy nanoparticles without excess unalloyed Fe species on the support as these Fe species lead to low propylene selectivity, coke deposition, and poor stability. Herein, we report an effective strategy to optimize the structure of PtFe bimetallic catalysts with minimal coke and high turnover frequency (8.2 s−1). For the optimized catalyst, 1Pt3Fe@S-1, most Fe species is in the framework of the zeolite S-1, which significantly suppresses the formation of coke. In addition, the extra-framework Fe and Pt species encapsulated in the channel of zeolite form uniform PtFe alloy nanoparticles, which significantly improves the C3H6 selectivity, catalytic stability, and recycling performance. These findings provide insights into the structure-performance relationship of PtFe bimetallic catalysts and shall be beneficial to future design and optimization of similar catalytic materials.

Surface modification of PtSn/Al2O3 catalyst by organic acid chelation and its effect on propane dehydrogenation performance

A series of Pt-based catalysts has been prepared by a chelating-agent-assisted impregnation method, and characterized by N2 adsorption/desorption, XRD, XPS, H2-TPR, NH3-TPD, pyridine-FTIR, CO-DRIFT-IR, Raman, and TG techniques to investigate the influence of organic acids on physicochemical properties. It was found that, except in the case of tartaric acid, organic acid-assisted preparation not only led to higher dispersion of Pt particles in comparison with organic acid-free catalyst PtSn/Al2O3, but also changed the concentration of Lewis acid sites and modified the interaction between the metallic Pt sites and the support. Experiments on the catalytic dehydrogenation of propane have revealed that the optimal dehydrogenation performance, with a propane conversion of 35% and a propylene selectivity of 93%, was obtained over the citric acid-assisted catalyst (PtSn/Al2O3-CA). Lewis acid sites are mainly responsible for activating C–H bonds during the tandem activation–cleavage process, whereas coke deposition and the aggregation of Pt sites are mainly responsible for deactivation of the catalyst.

Calcium‐Modified PtSn/Al2O3 Catalyst for Propane Dehydrogenation with High Activity and Stability

AbstractCatalytic dehydrogenation of propane to propylene and by‐product hydrogen is an atom‐economical and environmentally friendly route. PtSn/Al2O3 catalysts have been industrialized in this process, but still suffer from platinum sintering and coke deposition under reaction conditions. Herein, we design a calcium‐modified PtSn/Al2O3 catalyst showing a superior propane dehydrogenation performance. The presence of calcium combined with unsaturated aluminum and tin could consist of a new local microenvironment that promotes the dispersion of the platinum species and increases the electron density of the platinum species, which improves the catalytic activity, facilitates propylene desorption and inhibits coke formation. As a result, the achieved PtSnCa/Al2O3 catalyst exhibits a higher propylene formation rate and a lower coke‐accumulation rate compared to the catalyst without Ca addition. Moreover, the size of active phase clusters (∼1 nm) remained almost unchanged after the catalytic test, indicating a superior sintering resistance.