Selective and Stable Non-Noble-Metal Intermetallic Compound Catalyst for the Direct Dehydrogenation of Propane to Propylene

Screening and Mechanism Exploration of Non-Noble Metal Ni3M Catalysts for Propane Dehydrogenation: The Excellence of Synergistic Effects

The development of cost-effective and anti-coking catalysts for propane dehydrogenation (PDH) is crucial. Here, non-noble metal-incorporated Ni-based catalysts (Ni3M, M = Sc, Ti, V, Mn, Fe, Co, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn) were employed in the PDH process. The introduction of V, Nb, and Mo, with their strong carbon binding ability, created unique Ni-M cooperative sites, enhancing the catalytic performance. Other non-noble metals influenced the electronic structure of Ni, affecting the overall catalytic behavior. V and Nb exhibited a balanced combination of activity, selectivity, and stability, making them potential catalyst candidates. Microkinetic simulations revealed that Ni3V and Ni3Nb displayed high selectivity toward olefins with low apparent activation energies. This study emphasizes the significance of bimetallic synergy in enhancing PDH performance and provides new directions for the development of efficient alkane dehydrogenation catalyst development.

Intermetallic Ni3Ga1 Catalyst for Efficient Ammonia Reforming of Light Alkane

Ammonia reforming of light alkane is conventionally employed for HCN production where coproduct H2 is burned for heating owing to the high reaction temperature (1200 °C) of such a highly endothermic process. Here, we show that a Ni3Ga1 intermetallic compound (IMC) catalyst is highly efficient for such a reaction, realizing efficient conversion of C1-C3 alkanes at 575-750 °C. This makes it feasible for on-purpose COx-free H2 production assuming that ammonia, as an H2 carrier, is ubiquitously available from renewable energy. At 650 °C and an alkane/ammonia ratio of 1/2, ethane and propane conversion of ∼20% and methane conversion of 13% were obtained (with nearly 100% HCN selectivity for methane and ethane) over the unsupported Ni3Ga1 IMC, which also shows high stability due to the absence of coke deposition. This breakthrough is achieved by employing a stoichiometric Ni3Ga1 mixed oxalate solid solution as the precursor for the Ni3Ga1 IMC.

Proteomes reveal metabolic capabilities of Yarrowia lipolytica for biological upcycling of polyethylene into high-value chemicals

IMPORTANCE

Sustainable processes for biological upcycling of plastic wastes in a circular bioeconomy are needed to promote decarbonization and reduce environmental pollution due to increased plastic consumption, incineration, and landfill storage. Strain characterization and proteomic analysis revealed the robust metabolic capabilities of Yarrowia lipolytica to upcycle polyethylene into high-value chemicals. Significant proteome reallocation toward energy and lipid metabolisms was required for robust growth on hydrocarbons with n-hexadecane as the preferential substrate. However, an apparent over-investment in these same categories to utilize complex depolymerized plastic (DP) oil came at the expense of protein biosynthesis, limiting cell growth. Taken together, this study elucidates how Y. lipolytica activates its metabolism to utilize DP oil and establishes Y. lipolytica as a promising host for the upcycling of plastic wastes.

Ferric Single-Site Catalyst Confined in a Zeolite Framework for Propane Dehydrogenation

Non-oxidative dehydrogenation of propane is a highly efficient approach for industrial preparation of propene that is commonly catalyzed by noble Pt or toxic Cr catalysts and suffers from coking. In this work, ferric catalyst confined in a zeolite framework was synthesized by a hydrothermal procedure. The isolated Fe in the framework formed distorted tetrahedra, which were beneficial for the selective dehydrogenation of propane and reached over 95 % propene selectivity and over 99 % total olefins selectivity. This catalyst had a silanol-free structure and was oxygen tolerant, hydrothermally stable, and coke free, with a deactivation constant of 0.01 h-1 . This study provided guidance for the synthesis of structural heteroatomic zeolite and efficient propane non-oxidative dehydrogenation over early transition metals.

Tracking C-H bond activation for propane dehydrogenation over transition metal catalysts: work function shines

The activation of the C-H bond in heterogeneous catalysis plays a privileged role in converting light alkanes into commodity chemicals with a higher value. In contrast to traditional trial-and-error approaches, developing predictive descriptors via theoretical calculations can accelerate the process of catalyst design. Using density functional theory (DFT) calculations, this work describes tracking C-H bond activation of propane over transition metal catalysts, which is highly dependent on the electronic environment of catalytic sites. Furthermore, we reveal that the occupancy of the antibonding state for metal-adsorbate interaction is the key factor in determining the ability to activate the C-H bond. Among 10 frequently used electronic features, the work function (W) exhibits a strong negative correlation with C-H activation energies. We demonstrate that e^-W can effectively quantify the ability of C-H bond activation, surpassing the predictive capacity of the d-band center. The C-H activation temperatures of the synthesized catalysts also confirm the effectiveness of this descriptor. Apart from propane, e^-W applies to other reactants like methane.

Site Diversity and Mechanism of Metal-Exchanged Zeolite Catalyzed Non-Oxidative Propane Dehydrogenation

Metal-exchanged zeolites are well-known propane dehydrogenation (PDH) catalysts; however, the structure of the active species remains unresolved. In this review, existing PDH catalysts are first surveyed, and then the current understanding of metal-exchanged zeolite catalysts is described in detail. The case of Ga/H-ZSM-5 is employed to showcase that advances in the understanding of structure-activity relations are often accompanied by technological or conceptional breakthroughs. The understanding of Ga speciation at PDH conditions has evolved owing to the advent of in situ/operando characterizations and to the realization that the local coordination environment of Ga species afforded by the zeolite support has a decisive impact on the active site structure. In situ/operando quantitative characterization of catalysts, rigorous determination of intrinsic reaction rates, and predictive computational modeling are all significant in identifying the most active structure in these complex systems. The reaction mechanism could be both intricately related to and nearly independent of the details of the assumed active structure, as in the two main proposed PDH mechanisms on Ga/H-ZSM-5, that is, the carbenium mechanism and the alkyl mechanism. Perspectives on potential approaches to further elucidate the active structure of metal-exchanged zeolite catalysts and reaction mechanisms are discussed in the final section.

Catalytic Combustion of Propane over Ce-Doped Lanthanum Borate Loaded with Various 3d Transition Metals

Ce-doped LaBO3 (Ce0.05La0.95BO3) and a corresponding incorporation with 3d transition metals (TMs) were prepared and evaluated for eliminating propane. Our results showed the catalytic activity toward propane combustion has a close relationship with the loaded TMs, which promoted oxygen vacancies density and further enhanced the reduction and acidity of this material. This eventually led to 90% propane conversion at 718 K for a Cu-loaded Ce0.05La0.95BO3 catalyst. During 10 h of catalytic propane oxidation, the propane-elimination rate was maintained very well, with no degradation of the catalyst.

Ga+-Chabazite Zeolite: A Highly Selective Catalyst for Nonoxidative Propane Dehydrogenation

Ga-chabazite zeolites (Ga-CHA) have been found to efficiently catalyze propane dehydrogenation with high propylene selectivity (96%). In situ Fourier transform infrared spectroscopy and pulse titrations are employed to determine that upon reduction, surface Ga₂O₃ is reduced and diffuses into the zeolite pores, displacing the Brønsted acid sites and forming extra-framework Ga⁺ sites. This isolated Ga⁺ site reacts reversibly with H₂ to form GaH_x (2034 cm^-1) with an enthalpy of formation of ∼-51.2 kJ·mol^-1, a result supported by density functional theory calculations. The initial C₃H₈ dehydrogenation rates decrease rapidly (40%) during the first 100 min and then decline slowly afterward, while the C₃H₆ selectivity is stable at ∼96%. The reduction in the reaction rate is correlated with the formation of polycyclic aromatics inside the zeolite (using UV-vis spectroscopy) indicating that the accumulation of polycyclic aromatics is the main cause of the deactivation. The carbon species formed can be easily oxidized at 600 °C with complete recovery of the PDH catalytic properties. The correlations between GaH_x vs Ga/Al ratio and PDH rates vs Ga/Al ratio show that extra-framework Ga⁺ is the active center catalyzing propane dehydrogenation. The higher reaction rate on Ga⁺ than In⁺ in CHA zeolites, by a factor of 43, is the result of differences in the stabilization of the transition state due to the higher stability of Ga³⁺ vs In³⁺. The uniformity of the Ga⁺ sites in this material makes it an excellent model for the molecular understanding of metal cation-exchanged hydrocarbon interactions in zeolites.

Propane dehydrogenation over extra-framework In(i) in chabazite zeolites

Indium on silica, alumina and zeolite chabazite (CHA), with a range of In/Al ratios and Si/Al ratios, have been investigated to understand the effect of the support on indium speciation and its corresponding influence on propane dehydrogenation (PDH). It is found that In₂O₃ is formed on the external surface of the zeolite crystal after the addition of In(NO₃)₃ to H-CHA by incipient wetness impregnation and calcination. Upon reduction in H₂ gas (550 °C), indium displaces the proton in Brønsted acid sites (BASs), forming extra-framework In⁺ species (In-CHA). A stoichiometric ratio of 1.5 of formed H₂O to consumed H₂ during H₂ pulsed reduction experiments confirms the indium oxidation state of +1. The reduced indium is different from the indium species observed on samples of 10In/SiO₂, 10In/Al₂O₃ (i.e., 10 wt% indium) and bulk In₂O₃, in which In₂O₃ was reduced to In(0), as determined from the X-ray diffraction patterns of the product, H₂ temperature-programmed reduction (H₂-TPR) profiles, pulse reactor investigations and in situ transmission FTIR spectroscopy. The BASs in H-CHA facilitate the formation and stabilization of In⁺ cations in extra-framework positions, and prevent the deep reduction of In₂O₃ to In(0). In⁺ cations in the CHA zeolite can be oxidized with O₂ to form indium oxide species and can be reduced again with H₂ quantitatively. At comparable conversion, In-CHA shows better stability and C₃H₆ selectivity (∼85%) than In₂O₃, 10In/SiO₂ and 10In/Al₂O₃, consistent with a low C₃H₈ dehydrogenation activation energy (94.3 kJ mol⁻¹) and high C₃H₈ cracking activation energy (206 kJ mol⁻¹) in the In-CHA catalyst. A high Si/Al ratio in CHA seems beneficial for PDH by decreasing the fraction of CHA cages containing multiple In⁺ cations. Other small-pore zeolite-stabilized metal cation sites could form highly stable and selective catalysts for this and facilitate other alkane dehydrogenation reactions.

Indium-containing chabazite zeolites show better stability and C₃H₆ selectivity for propane dehydrogenation than In₂O₃, In/SiO₂ and In/Al₂O₃. Extra-framework In⁺ is identified as the stable active site upon reduction of an impregnated sample.

Tailoring Single-Atom Platinum for Selective and Stable Catalysts in Propane Dehydrogenation

Propane dehydrogenation has been a promising method for producing propylene that has the potentials to meet the increasing global demand for propylene. However, owing to the restricted equilibrium conversion caused by the high endothermicity, even the Pt-based catalysts, which exhibit high activity and selectivity, severely suffer significantly from coke formation and/or nanoparticle sintering at realistic reaction temperatures, resulting in a short catalyst lifetime. As a result, few innovative catalysts in terms of catalytic activity, selectivity, and stability, have been produced. In this Review, we focus on the characteristics of single-atom-like Pt sites for PDH and attempt to provide suggestions for developing highly efficient catalysts. First, we briefly describe the fundamental strategies. Following that, the remarkable catalysis is addressed by three different distinct sorts of state-of-the-art single-atom-like Pt catalysts are discussed. Additionally, we present other promising catalyst design approaches that are not based on single-atom-like Pt catalysts, as well as future research challenges in this field.

Fundamental understanding of the synthesis of well-defined supported non-noble metal intermetallic compound nanoparticles

Fundamental insights into the synthesis of model-like, supported, non-noble metal intermetallic compound nanoparticle catalysts with phase pure bulk and bulk-like 1st-atomic-layer particle surface composition.

Flowing-Air-Induced Transformation to Promote the Dispersion of the CrOx Catalyst for Propane Dehydrogenation

Highly dispersed chromium (Cr)-based catalysts are promising candidates for the catalytic dehydrogenation of propane (DHP). However, the easier aggregation of Cr species into crystalline Cr₂O₃ at the high-temperature calcination and reaction process is a big challenge, which severely restricts the improvement of activity and stability of the DHP reaction. Herein, a flowing-air-induced transformation method was first proposed, and the catalytic performance of the prepared Cr/MCM-41 catalysts was found to be significantly improved compared to that of the Cr-based catalyst prepared by the traditional calcination method, even better than that of most of the reported Cr-based catalysts and some noble metal-based catalysts. X-ray absorption spectroscopy and in situ Raman spectroscopy as well as other characterization techniques demonstrated that the in situ calcination in flowing air could not only effectively restrain the conversion of Cr(VI) into Cr(III) but also largely improve the dispersion of Cr species. Furthermore, DHP activity is found to have a positive correlation with the amount of monomeric Cr(VI) species, which is proved to be the precursor of active coordinatively unsaturated Cr sites. Our proposed flowing-air-induced transformation method provides a general strategy for preparing the highly dispersed Cr-based catalysts and other metal oxide materials with varied valence and exhibits potential application prospects in industry.

C-H bond activation in light alkanes: a theoretical perspective

Alkanes are the major constituents of natural gas and crude oil, the feedstocks for the chemical industry. The efficient and selective activation of C-H bonds can convert abundant and low-cost hydrocarbon feedstocks into value-added products. Due to the increasing global demand for light alkenes and their corresponding polymers as well as synthesis gas and hydrogen production, C-H bond activation of light alkanes has attracted widespread attention. A theoretical understanding of C-H bond activation in light hydrocarbons via density functional theory (DFT) and microkinetic modeling provides a feasible approach to gain insight into the process and guidelines for designing more efficient catalysts to promote light alkane transformation. This review describes the recent progress in computational catalysis that has addressed the C-H bond activation of light alkanes. We start with direct and oxidative C-H bond activation of methane, with emphasis placed on kinetic and mechanistic insights obtained from DFT assisted microkinetic analysis into steam and dry reforming, and the partial oxidation dependence on metal/oxide surfaces and nanoparticle size. Direct and oxidative activation of the C-H bond of ethane and propane on various metal and oxide surfaces are subsequently reviewed, including the elucidation of active sites, intriguing mechanisms, microkinetic modeling, and electronic features of the ethane and propane conversion processes with a focus on suppressing the side reaction and coke formation. The main target of this review is to give fundamental insight into C-H bond activation of light alkanes, which can provide useful guidance for the optimization of catalysts in future research.

Dehydrogenation of light alkanes to mono-olefins

In the past several decades, light alkane dehydrogenation to mono-olefins, especially propane dehydrogenation to propylene has gained widespread attention and much development in the field of research and commercial application. Under suitable conditions, the supported Pt-Sn and CrO_x catalysts widely used in industry exhibit satisfactory dehydrogenation activity and selectivity. However, the high cost of Pt and the potential environmental problems of CrO_x have driven researchers to improve the coking and sintering resistance of Pt catalysts, and to find new non-noble metal and environment-friendly catalysts. As for the development of the reactor, it should be noted that low operation pressure is beneficial for improving the single-pass conversion, decreasing the amount of unconverted alkane recycled back to the reactor, and reducing the energy consumption of the whole process. Therefore, the research direction of reactor improvement is towards reducing the pressure drop. This review is aimed at introducing the characteristics of the dehydrogenation reaction, the progress made in the development of catalysts and reactors, and a new understanding of reaction mechanism as well as its guiding role in the development of catalyst and reactor.

Metal-based catalysts for the non-oxidative dehydrogenation of light alkanes to light olefins

This review provides an overview of metal-based catalysts, including Pt-, Pd-, Rh- and Ni-based bimetallic catalysts for non-oxidative dehydrogenation of light alkanes to olefins.

Propane dehydrogenation: catalyst development, new chemistry, and emerging technologies

This review describes recent advances in the propane dehydrogenation process in terms of emerging technologies, catalyst development and new chemistry.

The impact of synthetic method on the catalytic application of intermetallic nanoparticles

Intermetallic alloy nanocrystals have emerged as a promising next generation of nanocatalyst, largely due to their promise of surface tunability. Atomic control of the geometric and electronic structure of the nanoparticle surface offers a precise command of the catalytic surface, with the potential for creating homogeneous active sites that extend over the entire nanoparticle. Realizing this promise, however, has been limited by synthetic difficulties, imparted by differences in parent metal crystal structure, reduction potential, and atomic size. Further, little attention has been paid to the impact of synthetic method on catalytic application. In this review, we seek to connect the two, organizing the current synthesis methods and catalytic scope of intermetallic nanoparticles and suggesting areas where more work is needed. Such analysis should help to guide future intermetallic nanoparticle development, with the ultimate goal of generating precisely controlled nanocatalysts tailored to catalysis.

Catalytic conversion of ethane to valuable products through non-oxidative dehydrogenation and dehydroaromatization

Chemical utilization of ethane to produce valuable chemicals has become especially attractive since the expanded utilization of shale gas in the United States and associated petroleum gas in the Middle East. Catalytic conversion to ethylene and aromatic hydrocarbons through non-oxidative dehydrogenation and dehydroaromatization of ethane (EDH and EDA) are potentially beneficial technologies because of their high selectivity to products. The former represents an attractive alternative to conventional thermal cracking of ethane. The latter can produce valuable aromatic hydrocarbons from a cheap feedstock. Nevertheless, further progress in catalytic science and technology is indispensable to implement these processes beneficially. This review summarizes progress that has been achieved with non-oxidative EDH and EDA in terms of the nature of active sites and reaction mechanisms. Briefly, platinum-, chromium- and gallium-based catalysts have been introduced mainly for EDH, including effects of carbon dioxide co-feeding. Efforts to use EDA have emphasized zinc-modified MFI zeolite catalysts. Finally, some avenues for development of catalytic science and technology for ethane conversion are summarized.

Single Vanadium Atoms Anchored on Graphitic Carbon Nitride as a High-Performance Catalyst for Non-oxidative Propane Dehydrogenation

In comparison with oil-based cracking technologies, the on-purpose dehydrogenation of propane (PDH) is a more eco-friendly and profitable approach to produce propylene. By means of density functional theory calculations, the present work reveals that the single vanadium (V) atom anchored on graphitic carbon nitride (V₁/g-C₃N₄) may serve as a promising single-atom catalyst for non-oxidative PDH with industrially practical activity, selectivity, and thermal stability. The high activity of V₁/g-C₃N₄ for PDH is attributed to the low-coordinated 3d orbitals of single V atoms, while the propylene selectivity is originated from the inhibition of the di-σ binding mode of propylene on the single V atoms. This work provides a guideline to design and screen out promising single-atom catalysts for selective dehydrogenation of alkanes.

Hydrogen Storage for Mobility: A Review

Numerous reviews on hydrogen storage have previously been published. However, most of these reviews deal either exclusively with storage materials or the global hydrogen economy. This paper presents a review of hydrogen storage systems that are relevant for mobility applications. The ideal storage medium should allow high volumetric and gravimetric energy densities, quick uptake and release of fuel, operation at room temperatures and atmospheric pressure, safe use, and balanced cost-effectiveness. All current hydrogen storage technologies have significant drawbacks, including complex thermal management systems, boil-off, poor efficiency, expensive catalysts, stability issues, slow response rates, high operating pressures, low energy densities, and risks of violent and uncontrolled spontaneous reactions. While not perfect, the current leading industry standard of compressed hydrogen offers a functional solution and demonstrates a storage option for mobility compared to other technologies.