Direct Dehydrogenation Of Propane Research Articles

Computational Exploration on Coupling Formic Acid Production with Propylene Synthesis via Catalytic Transfer Hydrogenation: The Role of CO2 beyond Reverse Water Gas Shift Reaction.

CO2-assisted propane dehydrogenation (CO2-ODHP) is emerging as an alternative route to the direct dehydrogenation of propane. Previous studies on CO2-ODHP have shown that the role of CO2 is to shift the reaction equilibrium toward the product side by consuming the produced H2 molecules via reverse water gas shift (RWGS) reaction. Since the ultimate fate of CO2 is to get reduced, we herein propose another pathway of CO2 reduction in the realm of CO2-ODHP─CO2 hydrogenation to formic acid (FA). With the objective of investigating the feasibility of this process, we, for the first time, carry out a computational investigation on coupling propane dehydrogenation with CO2 hydrogenation using a Ti-alkoxide-functionalized UiO-67 metal-organic framework. Analysis using the distortion/interaction model confirms that CO2 hydrogenation to FA is a preferred pathway over the RWGS reaction and hence can be realized in practice. Our study also highlights the importance of intersystem crossing, which provides an opportunity to access nonground state potential energy surfaces while undergoing chemical transformations. Again, subsequent addition of water molecules has shown to ease product desorption by 41 kcal/mol. Our study, therefore, hints at an unexplored role of CO2 beyond the RWGS reaction in oxidative propane dehydrogenation.

CO2‐mediated oxidative dehydrogenation of propane over Zn modified SSZ‐39 catalysts

To reveal the catalytic function of Brønsted acid sites (BAS) and different Zn Lewis acid sites (LAS) over SSZ‐39 and Zn modified SSZ‐39 in the direct dehydrogenation of propane (DHP) and CO­2‐mediated oxidative dehydrogenation (CO2‐ODHP) to propylene, a series of Zn‐modified H(Na)SSZ‐39 catalysts with various Zn loadings was prepared and conducted comparative studies between DHP and CO2‐ODHP. Detailed characterization results reveal the Zn‐loading‐dependent formation of Zn sites, primarily including Zn2+ and [Zn‐O‐Zn]2+, as well as their contributions in generating Lewis acid sites while neutralizing Brønsted acid sites of HSSZ‐39, namely bridged Si(OH)Al groups. In DHP, in comparison to bare HSSZ‐39, Zn/HSSZ‐39 catalysts exhibited a significantly enhanced C3H8 conversion. The presence of CO2 even further promoted C3H8 conversion in comparison to DHP. Given the above observations, we prepared Zn/NaSSZ‐39, in which the incorporation of Na further enriches the Lewis acid sites while neutralizing Brønsted acid sites of zeolite. Zn/NaSSZ‐39 even outperforms Zn/HSSZ‐39 catalysts with almost doubled C3H6 yield for CO2‐ODHP. The BAS has a poor CO2‐ODHP performance but can enhance the CO2 conversion towards CO significantly, while the Zn LAS is favorable for the CO2‐ODHP reaction, and plausible reaction paths of CO2‐ODHP on active sites are proposed.

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.

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.

Photothermal catalytic CO2 oxidative dehydrogenation of propane over a dual functional Pt-GaN/SrTiO3 catalyst

Photothermal CO2 oxidative dehydrogenation of propane (CO2-ODHP) is an environmentally friendly and sustainable route for propylene production and CO2 utilization. In the present work, we developed a Pt-GaN/SrTiO3 dual-functional catalyst to facilitate the reaction. The catalyst achieved propylene and CO yields of 1 mmol·gcat-1·h-1 and 1.2 mmol·gcat-1·h-1 under photothermal conditions at 320 °C, surpassing the performance of previously reported catalysts. Additionally, control experiments and in situ DRIFTS analyses corroborated that GaN and Pt were primarily responsible for the activation of C-H and CO bonds, respectively, and the photothermal route worked via a distinguished intermediate for CO2 activation in contrast to the thermal route. DFT calculations supported the reaction route involving the coupling direct dehydrogenation of propane and reverse water-gas shift reaction. The present work shines a light on the design of photothermal catalysts with dual functions, particularly for the activation of CO2 and light hydrocarbons. Additionally, it proposes a strategy to initiate high-temperature reactions at relatively lower temperatures.

Bimetallic PtZn nanoparticles anchored in high-silica SSZ-13 zeolite for efficient propane dehydrogenation

Direct dehydrogenation of propane to propylene (PDH) is a promising route to meet the ever-growing global propylene demand, but the industrial Pt-based catalysts usually suffer from serious deactivation derived from coke deposition and sintering under harsh reaction conditions. In this work, PtZn bimetallic nanoparticles encapsulated into high-silica SSZ-13 zeolites (PtZn@SSZ-13) were synthesized via a facile ligand-protected interzeolite transformation strategy. In a PDH reaction, the synthesized 0.5Pt3Zn@SSZ-13 catalyst exhibits superior catalytic performance with a propane conversion of 23.7% and a propylene selectivity of 96.8%, which is significantly better than that of PtZn supported on high-silica SSZ-13 (0.5Pt3Zn/SSZ-13). Particularly, the high catalytic activity of this catalyst can be kept during three successive oxidation–reduction cycles. Detailed characterizations including HAADF-STEM, XPS, UV–Vis, H2-TPR reveal that the remarkable improvement of PDH performance is attributed to the PtZn synergistic effect as well as the confinement of SSZ-13 zeolites. The DFT calculations and microkinetic simulations also evidenced that the Pt particles anchored on the Zn-doped SSZ-13 zeolite pore framework possessed obviously higher propane dehydrogenation activity, whereas the anti-coking ability of 0.5Pt3Zn@SSZ-13 was also stronger than Pt (111) surface, demonstrating the superior performance of 0.5Pt3Zn@SSZ-13.

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

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

Exploring the Properties of Silica Nanomaterials on Supporting Bimetallic PtZn Sites for Direct Propane Dehydrogenation

Exploring the Properties of Silica Nanomaterials on Supporting Bimetallic PtZn Sites for Direct Propane Dehydrogenation

Effect of Surface Acidity/Basicity of Cr/Zn−BEA Zeolite Catalysts on Performance in CO2‐PDH Process

AbstractThe influence of adding Cr(III) compounds into Zn−BEA zeolite samples (with silicate modulus Si/Al=17, 100, and 1000) on the redox and acid–base characteristics of Cr/Zn−BEA zeolites were studied, and their catalytic properties in propane dehydrogenation with CO2 to propylene. It was established (based on the XRD, low–temperature (77 K) ad/desorption of N2, TPR−H2, TPD−MSC−NH3(CO2), C3H8(C3H6), FTIR−Py data) that the acid–base characteristics of the surface of bifunctional Cr/Zn−BEA catalysts, namely the amount, strength, and nature (Lewis and Brønsted sites), determine their activity/selectivity, and operation stability in the process of CO2−PDH. This indicates that over Cr/Zn−BEA catalysts, the process runs along the route of direct propane dehydrogenation combined with the reverse water gas shift reaction.

Theoretical research on Pd cluster catalysts for the direct dehydrogenation of propane to propylene

AbstractIn this article, the feasibility of catalytic dehydrogenation of propane by Pd clusters (Pd7, Pd6C, Pd6Si, Pd6Ge, and Pd6Sn) was investigated by using density functional theory (DFT). It was found that Pd6Sn has the strongest electron mobility and the ability to activate CH bonds, and the highest adsorption barrier (−75.16 kcal/mol) with propylene. The first pathway of the Pd6Sn‐catalyzed primary reaction has the lowest decisive step barrier (16.65 kcal/mol), and the second pathway of the secondary reaction has the highest decisive step barrier (62.25 kcal/mol). It was demonstrated that both the catalyst's electron‐leaping ability and the ability to activate CH bonds were the key factors affecting the activity, and the adsorption strength of the catalyst to the product was the main factor affecting the selectivity. It was shown that Pd cluster‐catalyzed PDH is theoretically feasible and Pd6Sn is likely to be a potential cluster catalyst for propane dehydrogenation.

Design of MoS2 edge-anchored single-atom catalysts for propane dehydrogenation driven by DFT and microkinetic modeling.

The design of efficient catalysts for direct propane dehydrogenation (PDH) to inhibit coke formation and deactivation of traditional Pt-based catalysts are challenging tasks. Herein, by exploiting the unique geometric feature and tunability of single atom catalysts (SACs), a wide range of 3d-5d transition metals anchored on the MoS2 edge in the single atom form (TM1-S4/edge) are comprehensively investigated for the PDH application by first-principles calculations, ab initio molecular dynamics (AIMD) simulations and microkinetic modeling. Five criteria are assessed in terms of the feasibility of preparation, practical stability, feasibility of recovery after air oxidation, activity and selectivity. We identified Ru1-S4/edge SAC as the most promising candidate with activity six times higher than that of the conventional Pt(111) catalyst. Interestingly, AIMD simulations show that the motif region of the highly reactive TM1-S4/edge SACs (such as Ru, Os, Rh, and Ir) exhibits a dynamic change, with a TM-coordinated S atom tending to flutter at reaction temperatures and return to its initial position when the species is adsorbed on TMs, thereby affecting the PDH activities. In addition to identifying the potential PDH catalyst from a practical application point of view, we believe that this study also provides a comprehensive picture for the theoretical screening of low-coordination single-atom catalysts.

Recent Advances in Metal−Zeolite Catalysts for Direct Propane Dehydrogenation

Recent Advances in Metal−Zeolite Catalysts for Direct Propane Dehydrogenation

Tandem propane dehydrogenation and surface oxidation catalysts for selective propylene synthesis.

Direct propane dehydrogenation (PDH) to propylene is a desirable commercial reaction but is highly endothermic and severely limited by thermodynamic equilibrium. Routes that oxidatively remove hydrogen as water have safety and cost challenges. We coupled chemical looping-selective hydrogen (H2) combustion and PDH with multifunctional ferric vanadate-vanadium oxide (FeVO4-VOx) redox catalysts. Well-dispersed VOx supported on aluminum oxide (Al2O3) provides dehydrogenation sites, and adjacent nanoscale FeVO4 acts as an oxygen carrier for subsequent H2 combustion. We achieved an integral performance of 81.3% propylene selectivity at 42.7% propane conversion at 550°C for 200 chemical looping cycles for the reoxidization of FeVO4. Based on catalytic experiments, spectroscopic characterization, and theory calculations, we propose a hydrogen spillover-mediated coupling mechanism. The hydrogen species generated at the VOx sites migrated to adjacent FeVO4 for combustion, which shifted PDH toward propylene. This mechanism is favored by the proximity between the dehydrogenation and combustion sites.

Reaction mechanism of co-coupling conversion of propane and methanol over H-ZSM-5 zeolite

Co-coupling conversion of propane and methanol is an effective method to promote the activation of propane; however, the reaction mechanism has not been fully understood due to the complex reaction network. In this study, the reaction kinetics and thermodynamics of various elementary steps for propane activation under the assistance of methanol over H-ZSM-5 zeolite were systemically investigated by density functional theory (DFT) calculations combining with model experiments. The results show that direct dehydrogenation of propane on the acid sites of zeolite is very difficult, while introduction of methanol considerably decreases the free energy barrier for propane activation. This is because large amounts of active intermediates, such as surface methoxy and alkene-based species, are generated in methanol conversion that promote the propane dehydrogenation through hydrogen transfer reactions. Among these active intermediates, alkene-based species (including adsorbed alkene and tertiary carbocations) show higher activity towards C–H bond activation of propane.

Lewis acid-base modulation for efficient CO2 oxidative propane dehydrogenation: A case study of a La-modified binuclear Feoxo site

CO2 oxidative propane dehydrogenation to propylene (CO2-ODH) is promising for propylene production and CO2 utilization. Developing an efficient bifunctional CO2-ODH site capable of activating C–H and C=O bonds with inhibited C–C scission capacity remains a challenge. This work describes a La-modified binuclear Feoxo (La-Feoxo) site stabilized on a silicalite-1 support; it achieves 32.7% propane conversion (1.72 times higher than the direct propane dehydrogenation [PDH] counterpart) with 83.2% propylene selectivity. The promising CO2-ODH performance, attributed to the appropriate FeOx dispersion and La modification, balances the acid-base property, which helps stabilize key HCOO∗ intermediates toward enhanced CO2-assisted H removal efficiency. The inferior CO2-ODH performance of isolated Feiso and clustered Fe4O6 was rationalized by insufficient CO2 activation and huge dry reforming contribution, respectively. We propose H2 dissociative binding energy and O∗ binding energy as descriptors for the acid-base strength and catalytic CO2 dissociation capacity in that they predict the CO2-ODH and extent of propane dry reforming.

Density functional theory study on direct dehydrogenation of propane catalyzed by N-, O-, and P-doped graphene catalysts

The density functional theory was used to calculate the reaction mechanism and selectivity of nonmetallic single-atom catalysts, such as N, O, and P, doped on graphene in the direct dehydrogenation of propane (PDH) . Our results show that the rate-controlling step in PDH varies with the doping atom. We also found that N, O, and P nonmetallic single-atom-doped graphene catalysts showed relatively low adsorption performance for propane and the active site was the C atom adjacent to N, O, and P, rather than the doped atom itself. Interestingly, for the O-doped graphene catalysts, which can reduce the reaction energy barrier by searching for multiple transition states, and the more transition states in the reaction path, the lower the energy barrier for the reaction rate-controlling step. Finally, the results show that the energy barrier of P-doped propane direct dehydrogenation reflecting the speed control step is the lowest, which is 44.32 kcal·mol−1, and the energy barrier of deep dehydrogenation is 53.08 kcal·mol−1; so it has good selectivity. Therefore, the P-doped graphene catalyst has a promising application as a nonmetallic catalyst for the direct PDH, which provides the possibility for the design of cheap and environmentally friendly catalysts.

Boosting Propane Dehydrogenation by the Regioselective Distribution of Subnanometric CoO Clusters in MFI Zeolite Nanosheets.

Direct dehydrogenation of propane (PDH) has already been implemented worldwide in industrial processes to produce value-added propylene. The discovery of earth-abundant and environmentally friendly metal with high activity in C-H cleavage is of great importance. Co species encapsulated within zeolite are highly efficient for catalyzing direct dehydrogenation. However, exploring a promising Co catalyst remains a nontrivial target. Direct control of the regioselective distribution of Co species in the zeolite framework through altering their crystal morphology gives opportunities to modify the metallic Lewis acidic features, thus providing an active and appealing catalyst. Herein, we achieved the regioselective localization of highly active subnanometric CoO clusters in straight channels of siliceous MFI zeolite nanosheets with controllable thickness and aspect ratio. The subnanometric CoO species were identified by different types of spectroscopies, probe measurements, and density functional theory calculations, as the coordination site for the electron-donating propane molecules. The catalyst showed promising catalytic activity for the industrially important PDH with propane conversion of 41.8% and propylene selectivity higher than 95% and was durable during 10 successive regeneration cycles. These findings highlight a green and facile method to synthesize metal-containing zeolitic materials with regioselective metal distribution and also to open up a future perspectives for designing advanced catalysts with integrated advantages of the zeolitic matrix and metal structures.

Direct dehydrogenation of propane over Co@silicalite-1 zeolite: Steaming-induced restructuring of Co2+ active sites

The chemical state of the Co-relevant active site determines the catalytic performance of the Co-containing zeolite catalysts in non-oxidative propane dehydrogenation (PDH) reaction. Herein, we demonstrate that the moderate steaming pre-treatment is an available strategy to enhance catalytic activity of silicalite-1 zeolite-supported Co catalyst through tuning the Co state. The steaming-treated Co@S-1-steam catalyst exhibits sevenfold increased specific reaction rate (0.44 s−1) than the untreated Co@S-1 catalyst and maintains 95 % propylene selectivity in the PDH reaction at 590 °C. By comprehensive characterizations on the structural properties of the catalysts, multiple roles of steaming treatment are discovered. Steaming treatment can induce the reductive restructuring of the Co catalytic sites in zeolite micropores to form tetrahedral Co2+ species with enhanced dispersion and unsaturation degree, and significantly accelerate the selective activation of propane CH bonds. Furthermore, it also reduces the surface acidity and consequently promotes the desorption of propylene intermediates for enhancing the catalytic reaction rate and anti-coke stability.

Re-dispersion of active Zn species on modified S-1 zeolite as an efficient catalyst for direct dehydrogenation of propane

Highly active and inexpensive catalysts for propane dehydrogenation (PDH) are required for largescale propylene production in industrial application. Compared to Pt- and Cr-based catalysts, Zn-based nanomaterial is a promising candidate due to its environmental friendliness and coking-resistant but remains a great challenge. In this study, we developed a novel multi-component structure consisting of low Pt and abundant active Zn species highly dispersed on Fe-doped S-1 zeolite as PDH catalyst. Specifically, Fe-doping in S-1 support provided anchoring sites for loading Zn species with uniform distribution. Moreover, the very small amount of Pt was applied as promoter, which is beneficial to achieve the re-dispersion of Zn species with the formation of Znδ+ and Zn2+ active sites. The resulting 0.05Pt5Zn1Fe@S-1 catalyst exhibited the outstanding performance (conversion of propane: 40%, selectivity of propylene: 85%, and yield of propylene: 31.39%) as well as satisfactory regeneration ability. This improvement can be ascribed to the synergistic coupling between Pt promoter and the highly dispersed Zn species on modified S-1 support. This study opens a new way to design efficient and stable dehydrogenation catalysts.

Fluidized Bed Membrane Reactor for the Direct Dehydrogenation of Propane: Proof of Concept.

In this work, the fluidized bed membrane reactor (FBMR) technology for the direct dehydrogenation of propane (PDH) was demonstrated at a laboratory scale. Double-skinned PdAg membranes were used to selectively remove H2 during dehydrogenation tests over PtSnK/Al2O3 catalyst under fluidization. The performance of the fluidized bed membrane reactor was experimentally investigated and compared with the conventional fluidized bed reactor (FBR) by varying the superficial gas velocity over the minimum fluidization velocity under fixed operating conditions (i.e., 500 °C, 2 bar and feed composition of 30vol% C3H8-70vol% N2). The results obtained in this work confirmed the potential for improving the PDH performance using the FBMR system. An increase in the initial propane conversion of c.a. 20% was observed, going from 19.5% in the FBR to almost 25% in the FBMR. The hydrogen recovery factor displayed a decrease from 70% to values below 50%, due to the membrane coking under alkene exposure. Despites this, the hydrogen extraction from the reaction environment shifted the thermodynamic equilibrium of the dehydrogenation reaction and achieved an average increase of 43% in propylene yields.