Catalysts For Dehydrogenation Of Propane Research Articles

Constructing rich-Zn Pt1Zn1 alloy over the BEA zeolite as a selective catalyst for propane dehydrogenation

The deactivation of Pt-based catalysts is the most critical problem in nonoxidative propane dehydrogenation reaction (PDH), usually manifested in carbon deposition and active site sintering. Zn, as another cheap metal with more abundant reserves than Sn, is also widely used as an assistant in Pt-based catalysts. However, both of them are easy to be reduced to metal valence state and lost in the reaction process. Herein, the enlarged quantities of Zn are applied in the bimetallic Pt-Zn catalyst preparation. As confirmed by the increased reduction temperature of oxidized Zn species, it effectively minimizes the influence of the active metal mobility caused by Zn loss. At the same time, the constructed bimetallic structure modulates the surface acidity of Zn species and presents benign propylene desorption ability, thus the formed highly dispersed Pt sites on the surface of Pt1Zn1 alloy are well-matched with its high propylene selectivity (∼98.6%). In addition, the rich-Zn Pt1Zn1 sites are beneficial for enhancing the capability of resisting-coke, thus retarding the deactivation of this catalyst.

Off-Stoichiometric Restructuring and Sliding Dynamics of Hexagonal Boron Nitride Edges in Conditions of Oxidative Dehydrogenation of Propane.

Boron-containing materials, such as hexagonal boron nitride (h-BN), recently shown to be active and selective catalysts for the oxidative dehydrogenation of propane (ODHP), have been shown to undergo significant surface oxyfunctionalization and restructuring. Although experimental ex situ studies have probed the change in chemical environment on the surface, the structural evolution of it under varying reaction conditions has not been established. Herein, we perform global optimization structure search with a grand canonical genetic algorithm to explore the chemical space of off-stoichiometric restructuring of the h-BN surface under ambient as well as ODHP-relevant conditions. A grand canonical ensemble representation of the surface is established, and the predicted 11B solid-state NMR spectra are consistent with previous experimental reports. In addition, we investigated the relative sliding of h-BN sheets and how it influences the surface chemistry with ab initio molecular dynamics simulations. The B-O linkages on the edges are found to be significantly strained during the sliding, causing the metastable sliding configurations to have higher reactivity toward the activation of propane and water.

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.

Dimensional Understanding of Boron-Based Catalysts for Oxidative Propane Dehydrogenation: Structure and Mechanism

Dimensional Understanding of Boron-Based Catalysts for Oxidative Propane Dehydrogenation: Structure and Mechanism

Recent Progress on Catalyst Supports for Propane Dehydrogenation

Background: Propane dehydrogenation (PDH) is the most potential propylene production technology, which can make up the large gap in downstream products of propylene. The catalyst supports lay the foundation for the catalytic activity and stability of the prepared catalysts in PDH reactions. Therefore, we focus on the discussion of single oxides, composite oxides, zeolites, and carbon materials as supports to demonstrate the improvement of the catalytic performance of the PDH catalysts. Methods: Recent studies on catalyst supports are reviewed, including the preparation, characterization, and PDH performance. Results: The supports with different morphologies and crystal structures have been reported for PDH. The enhanced strong interaction between the support and metal components is responsible for the superior PDH performance. Conclusions: The PDH catalysts mainly depend on the development of the support with specific physicochemical properties for the corresponding PDH processes. Therefore, it is crucial to develop the optimal supports to improve the PDH performance in the area of nanoscience materials.

Ti-Doping in Silica-Supported PtZn Propane Dehydrogenation Catalysts: From Improved Stability to the Nature of the Pt-Ti Interaction.

Propane dehydrogenation is an important industrial reaction to access propene, the world's second most used polymer precursor. Catalysts for this transformation are required to be long living at high temperature and robust toward harsh oxidative regeneration conditions. In this work, combining surface organometallic chemistry and thermolytic molecular precursor approach, we prepared well-defined silica-supported Pt and alloyed PtZn materials to investigate the effect of Ti-doping on catalytic performances. Chemisorption experiments and density functional calculations reveal a significant change in the electronic structure of the nanoparticles (NPs) due to the Ti-doping. Evaluation of the resulting materials PtZn/SiO2 and PtZnTi/SiO2 during long deactivation phases reveal a stabilizing effect of Ti in PtZnTi/SiO2 with a kd of 0.015 h-1 compared to PtZn/SiO2 with a kd of 0.022 h-1 over 108 h on stream. Such a stabilizing effect is also present during a second deactivation phase after applying a regeneration protocol to the materials under O2 and H2 at high temperatures. A combined scanning transmission electron microscopy, in situ X-ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory study reveals that this effect is related to a sintering prevention of the alloyed PtZn NPs in PtZnTi/SiO2 due to a strong interaction of the NPs with Ti sites. However, in contrast to classical strong metal-support interaction, we show that the coverage of the Pt NPs with TiOx species is not needed to explain the changes in adsorption and reactivity properties. Indeed, the interaction of the Pt NPs with TiIII sites is enough to decrease CO adsorption and to induce a red-shift of the CO band because of electron transfer from the TiIII sites to Pt0.

Boosting propane dehydrogenation over Sn stabilizing dispersed Ptδ+ confined in Silicalite-1 at low temperature

Utilizing the confinement effect of zeolite pores to stabilize active sites has been developed for the improvement of catalytic stability and performance. Herein, a facile strategy is proposed to synthesize a Sn stabilizing dispersed Ptδ+ sites confined in zeolite pore catalyst via Ar calcination for propane dehydrogenation (PDH). 0.2Pt/0.5Sn-S-1-Ar shows excellent propylene formation rate of 10.0 mol C3H6·gPt−1·h−1 and propylene selectivity higher than 99.5% at 450 °C, and the superior catalyst stability in 200 h on-stream. And it has the lowest apparent activation energy barrier of 18.45 KJ/mol over Pt-based catalyst for PDH to our knowledge. According to systemic characterizations, it is demonstrated that the implantation of Sn into Silicalite-1 framework before introducing Pt is essential to generate the highly dispersed Ptδ+ species confined in zeolite pore, and the Ptδ+ species confined in zeolite pore with stronger propane adsorption and propylene desorption ability is responsible for superior PDH performance.

The stabilization effect of Al2O3 on unconventional Pb/SiO2 catalyst for propane dehydrogenation

The stabilization effect of Al2O3 on unconventional Pb/SiO2 catalyst for propane dehydrogenation

Clariant opens propane dehydrogenation catalyst production site in China

Clariant opens propane dehydrogenation catalyst production site in China

Support Effect of Ga-Based Catalysts in the CO2-Assisted Oxidative Dehydrogenation of Propane

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.

Regulating the C–H Bond Activation Pathway over ZrO2 via Doping Engineering for Propane Dehydrogenation

The efficient activation of the C–H bond in light alkanes and their catalyst design are significant for alkane-related catalytic processes in view of theoretical and practical aspects. Here, we report the C–H bond activation mechanism and structure–reactivity relationships of Ga-doped ZrO2 catalysts in propane dehydrogenation. Experimental and theoretical calculation results suggest that the introduction of Ga into the framework of ZrO2 alters the C–H bond activation pathway from a stepwise mechanism to a concerted mechanism involving simultaneous cleavage of two C–H bonds in propane, leading to a superior C–H bond activation ability and a lower reaction barrier than state-of-the-art metal oxide catalysts. In addition, a volcano-type dependence of the rate of propene formation on the Ga/Zr ratio is established due to a compromise of intrinsic activity and active site concentration. The strategy of metal incorporation into bulk metal oxide may provide an alternative solution to control the C–H bond activation pathway for efficient propene production.

Sn1Pt single-atom alloy evolved stable PtSn/nano-Al2O3 catalyst for propane dehydrogenation

The PtSn/Al2O3 is a prototypical industrial catalyst for propane dehydrogenation (PDH). However, the local structures of the active sites are still inconclusive under the operation conditions. Herein, the evolutions of the Pt-Sn active centers supported on nano-Al2O3 are definitely discerned at the atomic level during PDH reaction. By combining complementary in situ characterizations and theoretical calculations, we demonstrate that a highly productive Sn1Pt single-atom alloy (47.6 molC3H6 gPt–1 h–1) forms after the reduction, and thereby self-assembles to the Pt3Sn intermetallic compound during the reaction, which exhibits a rather stable performance (kd-10~40h: 0.0026 h–1). Intriguingly, the results of in situ diffuse reflectance infrared Fourier-transform spectroscopy further corroborate that the adjacent Pt atoms with terrace sites aggravating the coke deposition can be circumvented through this single-atom alloy mediated reconstruction. Our findings depict an unprecedented evolution process of the active sites of the PtSn/Al2O3, and afford an effectual nanostructure engineering pathway for stable PDH catalysts.

Progressive formation of active and stable PtZn bimetallic nanoclusters by exsolution during propane dehydrogenation

PtZn bimetallic nanoclusters on two-dimensional (2D) molecular sieves are attractive catalysts for propane dehydrogenation (PDH) owing to the ease of molecular diffusion, resistance to deactivation by coke deposition, and electronic promotion by Zn. Here, we report the progressive formation of highly active PtZn bimetallic nanoclusters on a Pt-modified zincosilicate with 2D delaminated MWW layers (PtZn-DML) under PDH conditions. The exsolution of Zn from the zincosilicate DML framework during PDH generates highly dispersed PtZn active sites and reduces the Lewis acidity of zincosilicate DML support, resulting in a high propane conversion (40.3%) comparable to thermodynamic equilibrium as well as extraordinary stability with a low deactivation rate (kd < 0.002 h−1) up to 13.6 days.

Sub-nanometer Pt2In3 intermetallics as ultra-stable catalyst for propane dehydrogenation

Pt-based catalysts are the typical industrial catalysts for propane dehydrogenation (PDH), which still suffer from insufficient long-term durability due to the structural instability and coke deposition. A commercial γ-Al2O3 supported thermally robust sub-nanometer Pt2In3 intermetallic catalyst with atomically ordered structure and rigorously separated Pt single atoms was fabricated, which showed outstanding robustness in 240 h long-term operation at 600 °C with the deactivation rate constant kd as low as 0.00078 h−1, ranking among the lowest reported values. Based on various in situ characterizations and theoretical calculations, it was proved that the catalyst stability not only resulted from the separated Pt single-atom sites but also significantly affected by the distance of adjacent Pt atoms. An increasing distance to 3.25 Å in the Pt2In3 could induce a weak π-adsorption configuration of propylene on Pt sites, which facilitated the desorption of propylene and restrained the side reactions like coking.

Comprehensive Mechanism and Microkinetic Model-Driven Rational Screening of 3N-Modulated Single-Atom Catalysts for Propane Dehydrogenation

Comprehensive Mechanism and Microkinetic Model-Driven Rational Screening of 3N-Modulated Single-Atom Catalysts for Propane Dehydrogenation

Zinc Speciation and Propane Dehydrogenation in Zn/H-ZSM-5 Catalysts

Zn/H-ZSM-5 catalysts have been frequently investigated for propane dehydrogenation (PDH); however, the active site remains unresolved due to the complexity of the system. We employed in situ FTIR spectroscopy and a kinetics method to correlate the Zn speciation and PDH activity in Zn/H-ZSM-5 with two Si/Al ratios (15 and 39) and a range of Zn/Al ratios (0–1.7). Incremental additions of zinc show that Zn2+ sites are preferentially formed on H-ZSM-5 over a fraction of paired Al sites followed by [Zn-O-Zn]2+ and [ZnOH]+ sites and then ZnOx clusters. The [Zn-OH]+ and [Zn-O-Zn]2+ sites in H-ZSM-5 are more active and selective than isolated Zn2+ for PDH. [Zn-OH]+ species sublimate over time on stream, leading to catalyst deactivation, while [Zn-O-Zn]2+ species are stable even after high-temperature reduction (750 °C for 60 min). Three distinct Zn sites ([Zn-O-Zn]2+, Zn2+, and [ZnOH]+) show a similar propane reaction order (close to 1) and H2 reaction order (close to 0). Combined with the lack of Zn hydride when propane flows over the catalyst at 550 °C, it is concluded that propane adsorption and dissociation is a rate-determining step and H2 desorption is fast. This work indicates that the preparation of H-ZSM-5 with abundant Al pairs may be a strategy to form stable and selective Zn/H-ZSM-5 catalysts for propane dehydrogenation. It is also highlighted that examining the effect of both metal/Al ratios and Al distribution of the zeolite is crucial in identifying the metal cations in metal–zeolite systems.

Design Strategies of Stable Catalysts for Propane Dehydrogenation to Propylene

Design Strategies of Stable Catalysts for Propane Dehydrogenation to Propylene

Strategies for regeneration of Pt-alloy catalysts supported on silica for propane dehydrogenation

Catalyst stability, resistance to deactivation, and regeneration remain a challenge for high temperature reaction processes. For Pt alloys used in propane dehydrogenation (PDH), the primary pathways of catalyst deactivation include coke formation and metal nanoparticle sintering over time. Recent work shows that silica-supported catalysts provide excellent selectivity for this reaction, but the regenerability of silica-supported catalysts has not been established. In this work, we study a series of Pt alloys, including PtMn, PtZn, and PtSn, for the PDH reaction at 550 °C and 600 °C, and we subject the catalysts to regeneration over multiple cycles. While oxidation in air restores the reactivity completely with minimal catalyst sintering, it is surprising to find that these catalysts can also be regenerated in pure hydrogen. Here we explore the types of coke formed on these catalysts using in situ temperature programmed oxidation (TPO). Two types of coke are found: one on the metallic NP surface, and a second on the silica support. Our work shows that treatment in hydrogen causes redistribution of the coke between the metal and support, which can restore most catalytic activity lost during a reaction run. Periodic introduction of H2 during a reaction cycle may constitute an unexplored strategy for extending the lifetime of PDH catalysts.

Coal as an Effective Catalyst for Selective Oxidative Dehydrogenation of Propane to Propene

Coal is a readily available and inexpensive material. However, its direct use as a catalyst is still rare, but attractive for practical application. In this paper, coal was directly used as a catalyst for the selective oxidative dehydrogenation of propane to propene. It exhibited a high selectivity over 90% with a yield of 8.4% at a high space velocity (12,000 mL·(h·g-cat)−1). The productivity up to 2.84 gC3H6 gcat−1 h−1 was obtained with propene selectivity above 80% (20,000 mL·(h·g-cat)−1). The kinetic showed first-order dependence with respect to propane or oxygen partial pressures. Meanwhile, electron paramagnetic resonance (EPR) and X-ray photoelectron spectrum (XPS) demonstrated that the carbonyl groups act as active sites for oxidative dehydrogenation of propane to propene. This work expands the use of earth-abundant and low-price coal in catalysis with expectable scale application.

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.