Propane Activation Research Articles

(Ga, Al)-H-MFI Catalysts with Highly Dispersed Ga Sites and Proximal Protonic Sites Enable Methane-Propane Coaromatization.

Methane-propane coaromatization (MPCA) upgrades two abundant and inexpensive light alkanes into value-added aromatic products. While Ga-loaded MFI zeolites represent by far the most promising catalysts for MPCA reaction, they often contain a sizable portion of Ga species at the external surface of zeolites, which are remote from the Brønsted acid sites (BAS) within MFI pores and thus inefficient for MPCA. Here, we show that Ga can be introduced into MFI pores at fairly high loadings via a simple cocrystallization approach, yielding catalysts possessing well-dispersed Ga sites predominantly residing inside the pores and framework. Adjacency between Ga and BAS within the constraints of MFI channels makes these (Ga, Al)-H-MFI catalysts more active toward methane and propane activation and more selective toward aromatics compared to the Ga/MFI counterparts prepared by impregnation that inevitably leaves a large fraction of Ga at the external surface (i.e., without confinement and few adjacent BAS). Further, the effects of the Si/Al ratio on MPCA performance have been investigated for (Ga, Al)-H-MFI catalysts. Due to the multifold roles of BAS in the overall reaction sequence, an increased BAS concentration generally results in higher propane conversion and productivity of aromatics together with lower net methane conversion and severer coking.

Theoretical investigation on propane dehydrogenation over extraframework Ga hydride species trapped at Al-pairs in MFI zeolite

Ga/ZSM-5 is widely used to catalyze propane dehydrogenation (PDH). For the harsh operation conditions, the detailed active species, and the plausible reaction pathways that are responsible for the observed superior PDH performance remain unresolved for Ga/ZSM-5. Reduced extraframework Ga hydride species trapped at zeolite framework Al-pairs, including b[GaH]2+, [Ga]+-BAS, [GaH2]+-BAS, etc. are an important kind of Ga species known as active species for PDH. In this work, the PDH pathways these over these Ga species were investigated theoretically at temperatures and pressures relevant to experiments. We showed that dynamically generated undercoordinated b[GaH]2+ would exhibit significantly higher catalytic activity at PDH conditions as compared with other Ga hydride species. The most plausible PDH pathway over b[GaH]2+ is the carbenium pathway. The Ga species and BAS act in concert in promoting the H2 elimination and β-H transfer, and in turning PDH efficient. Ga hydride species may also form as intermediates along the PDH pathways as active sites for subsequent activation and conversion of propane, suggesting the evolution of Ga hydride species trapped by Al-pairs in Ga/ZSM-5 at operation conditions. The findings are expected to pave the way for better understanding of the experimentally observed operation condition dependent PDH performance of Ga/ZSM-5.

Highly efficient Ru/CeO2 catalyst using colloidal chemical method for propane oxidation

Although supported-Ru catalysts have been widely studied for the light alkane oxidation root in their lower cost compared to Pt and Pd, developing Ru-based catalysts with high efficiency for low-temperature light alkane elimination remains a significant challenge. Herein, Ru/CeO2 catalysts were prepared utilizing the colloidal synthesis (Ru/CeO2-CS) and compared with the catalyst prepared with the traditional impregnation method (Ru/CeO2-IM) in the textural properties and catalytic propane oxidation. It was discovered that Ru/CeO2-CS sample contained a higher concentration of active Ru − O − Ce interface and oxygen vacancies attributed to the strong Ru-CeO2 interaction, which further enhanced the redox capacity. Besides, the lower valence state of Ru species and higher contents of Lewis acid sites on Ru/CeO2-CS sample boosted the adsorption, dissociation, and activation of propane, thus promoting the deep oxidation of propane to CO2 and H2O. The reaction mechanism of propane oxidation was revealed by in-situ DRIFTS, and both the catalysts showed bands related to acrylate species, suggesting that propane underwent an acrylate oxidation pathway on Ru/CeO2-CS and Ru/CeO2-IM samples. The distinct textural properties of these catalysts resulted in Ru/CeO2-CS synthesized by colloidal methods showing a T90 of 170 °C, and Ea of 50.9 ± 1.8 kJ·mol−1, markedly lower than Ru/CeO2-IM prepared with the traditional impregnation method. Apart from the activity, the Ru/CeO2-CS sample obtained superior water resistance, thermal stability, and durability. This comprehensive work provides promising insights into low-temperature propane oxidation.

C–H bond activation of propane on Ga2O22+ in Ga/H-ZSM-5 and its mechanistic implications

C–H bond activation of propane on Ga2O22+ in Ga/H-ZSM-5 and its mechanistic implications

Mn/CeO2 contains enriched surface lewis acid sites and pore structures accelerated catalytic oxidation of propane at low temperature

The development of highly efficient non-precious metal catalysts for the low-temperature catalytic oxidation of volatile organic compounds (VOCs) is a critical imperative in VOCs control. In this study, a series of highly active CeMnOx catalysts with Mn-doped CeO2 were investigated. The catalysts (WHSV=30,000 mL g−1 h−1) exhibited the highest catalytic propane oxidation activity (T90 = 230 °C) and excellent stability over 600 h, When the Mn:Ce ratio was 2.5. The introduction of Mn doping resulted in modifications to the pore structure of CeO2, leading to an increase in specific surface area and enhanced gas transfer kinetics. Additionally, it induced surface electronic defects and elevated the concentration of acidic sites, thereby facilitating the adsorption and activation of propane. Consequently, these improvements contributed to an enhanced catalytic performance of the catalyst. The in-situ DRIFTS infrared spectra revealed that Mn doping reduced the activation energy of the reaction and facilitated the conversion of acetone groups as well as decomposition of carboxylic acid groups.

In Situ Formation of B═O Bond in Oxidative Dehydrogenation of Propane and as a Hunter for Alkoxyl Radicals: A Computational Study.

B═O multiple bonds are fundamentally important owing to the unique property of B and its potential as a tool in catalysis. Herein by means of DFT calculations, we investigated the in situ generation of transient -B═O species in the nonmetallic inorganic boron oxides and demonstrated its superior ability to capture alkoxyl radicals under the conditions of oxidative dehydrogenation of propane (ODHP). Boron-containing materials are emerging as promising catalysts for ODHP, while an extensive understanding of the underlying mechanisms remains challenging. Through systematic mechanistic and characterization calculations, we show the feasibility for the presence of -B═O species under ODHP conditions and propose that its π nature dictates its inertness in the C-H activation of propane (ΔG⧧ = 57 kcal/mol) but offers its strong ability in capturing alkoxyl radicals (barrierless with ΔG = -30 kcal/mol), which can then transform to the ·C3H6OH radical. This explains the observation of enol in the experimental study. This specific behavior of the -B═O species makes it one of the key players in the complex reaction network of ODHP and also implicates the rational design of scavengers for reactive oxygen species (ROS) and other active oxygenated species.

Mechanistic understanding of oxygen spillover enables efficient propane combustion over Pt/AlSOx catalyst

Understanding of the mechanism of saturated alkanes catalytic combustion is crucial for the petrochemical industrial exhaust elimination. Noble metals are commonly proposed to be the active sites for C–H bond activation of saturated alkanes, whereas the critical role of support is largely underestimated. Herein, we reveals a novel pathway for propane activation and combustion on acidic support of Pt catalyst, driven by oxygen spillover, which differs significantly from previously reported reaction mechanisms. Specifically, the Pt/AlSOx-I catalyst was prepared by pyrolyzing the Al2(SO4)3 sol–gel to obtain the acidic micro-mesoporous AlSOx support, followed by loading the Pt active sites using wetness impregnation. In comparison to Pt catalysts supported by Al2O3 nanoparticles (10 nm) or commercially available common γ-Al2O3, the Pt/AlSOx-I catalyst demonstrates superior catalytic activity for propane combustion. It is found that gaseous oxygen species activated on Pt active sites spillovers to acidic support of Pt/AlSOx-I and then drives propane to activation and further oxidation on acidic support, thereby remarkably decreasing the apparent activation energies (Ea) from 112.4 to 72.0 kJ·mol−1. Kinetic results suggest that the negative effect of oxygen competitive adsorption is weakened because propane can be activated on the acidic AlSOx support. Additionally, high proportion of metallic Pt species benefits to gaseous oxygen activation as observed on Pt/AlSOx-R, leading to the further increased catalytic activity with highest specific mass reaction rate of 170.2 μmol gPt−1 s−1 and TOFPt of 0.289 s−1 at 220 °C. Our primary results provide novel insights into revealing the reaction mechanism of saturated alkanes combustion on dual active sites.

Confining platinum clusters in indium-modified ZSM-5 zeolite to promote propane dehydrogenation

Designing highly active and stable catalytic sites is often challenging due to the complex synthesis procedure and the agglomeration of active sites during high-temperature reactions. Here, we report a facile two-step method to synthesize Pt clusters confined by In-modified ZSM-5 zeolite. In-situ characterization confirms that In is located at the extra-framework position of ZSM-5 as In+, and the Pt clusters are stabilized by the In-ZSM-5 zeolite. The resulting Pt clusters confined in In-ZSM-5 show excellent propane conversion, propylene selectivity, and catalytic stability, outperforming monometallic Pt, In, and bimetallic PtIn alloys. The incorporation of In+ in ZSM-5 neutralizes Brønsted acid sites to inhibit side reactions, as well as tunes the electronic properties of Pt clusters to facilitate propane activation and propylene desorption. The strategy of combining precious metal clusters with metal cation-exchanged zeolites opens the avenue to develop stable heterogeneous catalysts for other reaction systems.

Robust Ru/Ce@Co Catalyst with an Optimized Support Structure for Propane Oxidation.

Short carbon chain alkanes, as typical volatile organic compounds (VOCs), have molecular structural stability and low molecular polarity, leading to an enormous challenge in the catalytic oxidation of propane. Although Ru-based catalysts exhibit a surprisingly high activity for the catalytic oxidation of propane to CO2 and H2O, active RuOx species are partially oxidized and sintered during the oxidation reaction, leading to a decrease in catalytic activity and significantly inhibiting their application in industrial processes. Herein, the Ru/Ce@Co catalyst is synthesized with a specific structure, in which cerium dioxide is dispersed in a thin layer on the surface of Co3O4, and Ru nanoparticles fall preferentially on cerium oxide with high dispersity. Compared with the Ru/CeO2 and Ru/Co3O4 catalysts, the Ru/Ce@Co catalyst demonstrates excellent catalytic activity and stability for the oxidation of propane, even under severe operating conditions, such as recycling reaction, high space velocity, a certain degree of moisture, and high temperature. Benefiting from this particular structure, the Ru/Ce@Co (5:95) catalyst with more Ce3+ species leads to the Ru species being anchored more firmly on the CeO2 surface with a low-valent state and has a strong potential for adsorption and activation of propane and oxygen, which is beneficial for RuOx species with high activity and stability. This work provides a novel strategy for designing high-efficiency Ru-based catalysts for the catalytic combustion of short carbon alkanes.

Kinetic modeling of the oxidative dehydrogenation of propane with CO2 over a CrOx/SiO2 catalyst and assessment of CO2 utilization

Oxidative dehydrogenation of propane with carbon dioxide (ODPC) has gained attention as a sustainable process capable of simultaneously producing propylene and reducing carbon dioxide (CO2) emissions. In this study, we developed a kinetic model of the ODPC over a silica-supported chromium oxide catalyst based on the Mars–van Krevelen (MvK) mechanism using the experimental data obtained under controlled conditions. The constructed model estimated both reactant conversions and propylene yield within an absolute error of 3% of the experimental data, confirming the integrity of the kinetic model. The kinetic analysis provides insight into the activation of propane and CO2 via several reactions occurring under ODPC conditions, emphasizing that the ODPC cycle is limited by the high energy barrier for CO2 activation. In addition, it allows comparison of the contributions of non-oxidative and oxidative dehydrogenation reactions, the two main reactions producing propylene under ODPC conditions. The estimation results show a significant increase in the reaction rate of ODPC with increasing CO2 partial pressure, in contrast to a nearly constant reaction rate of non-oxidative dehydrogenation, highlighting the promoting effect of CO2 in enhancing the ODPC reaction. Furthermore, the potential of the ODPC process is assessed by considering propylene productivity, net CO2 emissions, including the energy consumption for the separation process, and the global warming index of the energy grid. A comprehensive investigation of the ODPC process through controlled experiments, kinetic modeling and evaluation of net CO2 utilization provides insight into future strategies for using the ODPC as an efficient and eco-friendly process.

Selective C-H Bond Activation in Propane with Molecular Oxygen over Cu(I)-ZSM-5 at Ambient Conditions.

Selective activation of C-H bonds in light alkanes under mild conditions is challenging but holds the promise of efficient upgrading of abundant hydrocarbons. In this work, we report the conversion of propane to propylene with ∼95% selectivity on Cu(I)-ZSM-5 with O2 at room temperature and pressure. The intraporous Cu(I) species was oxidized to Cu(II) during the reaction but could be regenerated with H2 at 220 °C. Diffuse reflectance ultraviolet spectroscopy indicated the presence of both Cu+-O2 and Cu2(μ-O2)2+ species in the zeolite pores during the reaction, and electron paramagnetic resonance results showed that propane activation occurred via a radical-mediated pathway distinct from that with H2O2 as the oxidant. Correlation between spectroscopic and reactivity results on Cu(I)-ZSM-5 with different Cu loadings suggests that the isolated intraporous Cu(I) species is the main active species in propane activation.

Novel strategy to regulate the geometric and electronic structure of Pt catalyst for efficient propane combustion

The geometric and electronic structure of Pt active sites plays a crucial role in determining the catalysts performance, but precise regulation remains challenging. Herein, we propose a novel approach to modulate the nature of Pt active sites by combining photo-deposition of Pt nanoparticles with ultra-low Mo loading (0.1 wt%) modification on Pt/SiO2 catalysts. The addition of ultra-low loading Mo promoter not only effectively reduces the size of Pt particles but also donates electrons to the Pt particles. Furthermore, the photo-deposited Pt particles exhibit a higher proportion of metallic Pt species, which is more stable than that metallic Pt species obtained by H2 reduction, compared to those prepared using traditional wetness impregnation methods. Propane oxidation activity evaluations confirm that the photo-deposited and Mo-modified Pt/0.1Mo/SiO2-P catalyst exhibits the highest activity among all the prepared catalysts. Combined with experiments of C3H8-TPSR and in-situ DRIFT spectra of propane oxidation, it is found that the Pt/0.1Mo/SiO2-P catalyst remarkably promotes propane activation and C-H bond cleavage due to the nature change of Pt active sites, and the presence of gaseous oxygen benefits propane cleavage on active sites. Our primary results provide a promising strategy for designing superior platinum catalysts by regulating Pt active sites nature for efficient propane complete oxidation.

Facile construction and enhanced catalytic activity of Co-Mn oxide with rich amorphous/crystalline interfaces for propane oxidation

Cobalt-manganese (Co-Mn) composite oxides show high potential for the catalytic oxidation of volatile organic compounds (VOCs). However, the low defect content and poor oxygen mobility of perfect spinel structure crystalline always make it difficult to effectively activate C–H bonds of propane. Here, the catalyst with rich amorphous MnOx/crystalline Co3O4 interfaces was prepared, and the catalytic combustion activity for propane was determined. The rich amorphous/crystalline interfaces CMO-400 (i.e. Co-Mn oxide calcined at 400 °C) catalyst exhibited the best catalytic activity for propane with T90 of 200 °C among all bimetallic Co-Mn oxides. Various characterizations and corresponding results have demonstrated that the abundant amorphous/crystalline interfaces could improve the catalytic performances, attributed to high oxygen vacancy concentration, low temperature reducibility, weak Mn−O bond strength, and good surface lattice oxygen mobility. It is noteworthy that the interface engineering of amorphous/crystalline is an effective strategy in VOCs catalytic oxidation.

Deep Potential Molecular Dynamics Study of Propane Oxidative Dehydrogenation.

Oxidative dehydrogenation (ODH) of light alkanes is a key process in the oxidative conversion of alkanes to alkenes, oxygenated hydrocarbons, and COx (x = 1,2). Understanding the underlying mechanisms extensively is crucial to keep the ODH under control for target products, e.g., alkenes rather than COx, with minimal energy consumption, e.g., during the alkene production or maximal energy release, e.g., during combustion. In this work, deep potential (DP), a neural network atomic potential developed in recent years, was employed to conduct large-scale accurate reactive dynamic simulations. The model was trained on a sufficient data set obtained at the density functional theory level. The intricate reaction network was elucidated and organized in the form of a hierarchical network to demonstrate the key features of the ODH mechanisms, including the activation of propane and oxygen, the influence of propyl reaction pathways on the propene selectivity, and the role of rapid H2O2 decomposition for sustainable and efficient ODH reactions. The results indicate the more complex reaction mechanism of propane ODH than that of ethane ODH and are expected to provide insights in the ODH catalyst optimization. In addition, this work represents the first application of deep potential in the ODH mechanistic study and demonstrates the ample advantages of DP in the study of mechanism and dynamics of complex systems.

Efficient conversion of propane in a microchannel reactor at ambient conditions

The oxidative dehydrogenation of propane, primarily sourced from shale gas, holds promise in meeting the surging global demand for propylene. However, this process necessitates high operating temperatures, which amplifies safety concerns in its application due to the use of mixed propane and oxygen. Moreover, these elevated temperatures may heighten the risk of overoxidation, leading to carbon dioxide formation. Here we introduce a microchannel reaction system designed for the oxidative dehydrogenation of propane within an aqueous environment, enabling highly selective and active propylene production at room temperature and ambient pressure with mitigated safety risks. A propylene selectivity of over 92% and production rate of 19.57 mmol mCu−2 h−1 are simultaneously achieved. This exceptional performance stems from the in situ creation of a highly active, oxygen-containing Cu catalytic surface for propane activation, and the enhanced propane transfer via an enlarged gas-liquid interfacial area and a reduced diffusion path by establishing a gas-liquid Taylor flow using a custom-made T-junction microdevice. This microchannel reaction system offers an appealing approach to accelerate gas-liquid-solid reactions limited by the solubility of gaseous reactant.

Engineering Mn–O strength in manganese oxide catalyst to enhance propane catalytic oxidation

Developing highly active and thermally stable transition-metal-oxide catalysts for light alkane catalytic oxidation is of great importance but very challenging. In the work, the catalytic performance for propane deep oxidation was significantly enhanced on the Mn1NixOy solid solution catalyst by weakening the Mn–O bond strength of manganese oxide. The characterization results combined with DFT calculations demonstrated that the introduction of Ni could create additional defect sites, resulting in a significant improvement of the adsorption and the activation of both propane and oxygen molecules. The optimal Mn1Ni0.15Oy catalyst exhibits abundant oxygen vacancies with low MnO bond strength, high redox ability and oxygen mobility, which account for its superior activity. Specifically, the specific reaction rate on Mn1Ni0.15Oy is three times higher than that on pure Mn2O3. Moreover, a Mn1Ni0.15Oy/cordierite monolithic catalyst was made by wash-coating method, and exhibited remarkable catalytic performance and stability on catalytic oxidation of propane during the 45 days (1080 h) on stream, even after tens of high temperature thermal shocks (up to 650 ℃), which declared to be satisfied for practical industrial applications. This work will shed light on designing high-efficiency and long-life environmental catalyst for VOCs elimination.

In-situ modulation of α-MnO2 surface oxygen vacancies for photothermal catalytic oxidation of propane: Insights into activity and synergistic mechanism

Crystallographic effects in photothermal synergistic catalytic oxidation (PTSCO) system for VOCs removal are essential but still lack in-depth systematic studies. Therefore, key factors and synergistic mechanism of propane removal by MnO2 with different crystal planes in PTSCO system were investigated. The results showed that 160-M−300 with the mainly exposed (110) crystal plane displayed the optimal activity (T90 = 235℃, TOF = 4.90 × 10-7·s−1) and long-term stability (40 h) due to the abundant oxygen vacancies (OVs) controlled by the crystal planes, outstanding low temperature reduction ability and higher oxygen mobility. OVs substantially enhanced the adsorption and activation of propane and O2, and accelerated the efficient separation of photogenerated electrons and holes by capturing the electrons. Correspondingly, density functional theory (DFT) calculations confirmed that (110) crystal facet had the lowest OVs generation energy and work function, based on which, a multi-pathway enhancement mechanism of PTSCO was proposed. This study clarified the crystal-PTSCO activity dependence, provided theoretical support for the efficient and energy-saving removal of low-carbon alkanes.

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.

Efficient Screening of Metal Promoters of Pt Catalysts for C-H Bond Activation in Propane Dehydrogenation from a Combined First-Principles Calculations and Machine-Learning Study.

Platinum-based materials are the most widely used catalysts in propane direct dehydrogenation, which could achieve a balanced activity between both propane conversion and propene formation. One of the core issues of Pt catalysts is how to efficiently activate the strong C-H bond. It has been suggested that adding second metal promoters could greatly solve this problem. In the current work, first-principles calculations combined with machine learning are performed in order to obtain the most promising metal promoters and identify key descriptors for control performance. The combination of three different modes of adding metal promoters and two ratios between promoters and platinum sufficiently describes the system under investigation. The activity of propane activation and the formation of propene are reflected by the increase or decrease of the adsorption energy and C-H bond activation of propane and propene after the addition of promoters. The data of adsorption energy and kinetic barriers from first-principles calculations are streamed into five machine-learning methods including gradient boosting regressor (GBR), K neighbors regressor (KNR), random forest regressor (RFR), and AdaBoost regressor (ABR) together with the sure independence screening and sparsifying operator (SISSO). The metrics (RMSE and R2) from different methods indicated that GBR and SISSO have the most optimal performance. Furthermore, it is found that some descriptors derived from the intrinsic properties of metal promoters can determine their properties. In the end, Pt3Mo is identified as the most active catalyst. The present work not only provides a solid foundation for optimizing Pt catalysts but also provides a clear roadmap to screen metal alloy catalysts.

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.