High Propylene Selectivity Research Articles

Enhanced microwave-catalytic performance for CO2 oxidative propane dehydrogenation by acidified and Bi-doped ZnO-based microwave catalysts

The oxidative dehydrogenation of propane by carbon dioxide (CO2-ODHP) has great potential in producing propylene. Resource utilization of CO2 will be the dominant trend in the future to mitigate environmental problems and cope with the growth in energy demand. However, simultaneously achieving high propane conversion, high propylene selectivity, and high CO2 conversion at low temperatures remains challenging. Herein, we report a novel efficient microwave catalyst (1.0-Zn4Bi1/Silicalite-1+SiC) by doping Bi on ZnO/Silicalite-1 and then acid treatment. The (1.0)-Zn4Bi1/Silicalite-1+SiC microwave catalyst exhibited 92 % C3H8 conversion, 84 % C3H6 selectivity, and 45 % CO2 conversion under microwave mode, significantly better than under the thermocatalysis (without microwave: 27 % C3H8 conversion, 92 % C3H6 selectivity, and 14 % CO2 conversion). The CO2 capture capacity was improved by adding Bi to ZnO/Silicalite-1. In addition, acid modification increased the propane and CO2 conversion by 1.9 and 1.3 times, respectively. Notably, acid treatment enriched the pore structure of the catalysts, altered surface acidity and alkalinity, and promoted C3H8 and CO2 activation and C3H6 desorption. In particular, the acid treatment enriches the state of the presence of Zn species in the catalyst. Microwave irradiation reduces the apparent activation energy of the catalytic system and accelerates the removal of coke from the catalyst surface. Microwave catalysis can activate CO2 and propane at lower temperatures than thermocatalysis.

A Smart Design of Non-Noble Catalysts for Sustainable Propane Dehydrogenation.

Propane dehydrogenation (PDH), an important process for propylene synthesis, relies on expensive noble metals or highly toxic oxides as catalysts. In a recent publication, Gong and co-workers report a breakthrough discovery for PDH by introducing a sustainable catalyst composed of titanium oxide overlayers encapsulating nickel nanoparticles, termed Ni@TiOx. This innovative catalyst showcases exceptional performance in PDH, exhibiting high propylene selectivity and stability under industrially relevant conditions. The study elucidates the role of defective TiOx overlayers and the electronic promotional effect of subsurface Ni in enhancing catalytic activity, translating a traditional model catalyst system into a sustainable industrial catalyst for low-carbon energy and the chemical industry.

High stable PtZnLa/Beta catalyst with low Pt loading for propane dehydrogenation

A high stable and active Pt-Zn-La/Beta catalyst with 0.1 wt% Pt loading was studied for catalyzing propane dehydrogenation (PDH) in this work, which is constructed by anchoring La and Zn species onto silanol nests of Beta zeolite at first and then loading Pt on the resultant material after calcination. It is found that the Beta zeolite with the Si/Al ratio of 9.75 is more appropriate than the one with higher Si/Al ratio to be used as the support after the dealumination. And that anchoring La and Zn species prior to Pt onto the silanol nests are quite important. In Pt0.1Zn0.4La0.4/Beta catalyst, La significantly dispersed and stabilized Pt1Zn1 ensembles on the zeolite surface while Zn isolated the Pt atoms and therefore the catalyst is much active, highly selective and catalytic stable. With this catalytic structure, the catalyst provided a high initial propylene formation rate of 113.8 molC3H6·gPt−1·h−1 with extremely low deactivation constant of 0.0149 h−1 and a high propylene selectivity of 98 % at 600 °C.

Evolution of the Active Phase of Pt/Sn-Al2O3 Catalysts During Acidic Impregnation and Their Use in Propane Dehydrogenation.

Alumina-supported PtSn is an industrialized catalyst for propane dehydrogenation. During the catalyst impregnation, the acidic impregnation solution with chloroplatinic acid as a precursor inevitably leads to the partial dissolution of the surface of amphoteric alumina support and finally varies catalytic performance. Herein, the structure evolution of the active phase, induced by an impregnated acidic solution, was studied with special care. According to the diffused double layer theory, we proposed a model of microgels during impregnation. The microgels formed in the solution with suitable acidity on the surface of the catalysts evolved into a structure of Al2O3-coated oxidized Pt by reprecipitation during drying and calcination. The covered Pt species could be exposed by Ar+ sputtering or migrate to the surface during reduction to serve as active sites for propane dehydrogenation. Noticeably, the surface Sn0 species was generated when the pH of the impregnated solution was around 0.56, which is solid proof for the unique active phase with the PtSn alloy present on SnOx species existing on the surface of the Sn-Al2O3 support. The synthesized catalyst exhibited high propylene selectivity (99.4%) and superior stability (kd = 0.002 h-1). This study provides new insight for the precise preparation of Pt/Sn-Al2O3 catalysts.

Silanol-Stabilized Atomically Dispersed Ptδ+-Ox-Sn Active Sites in Protozeolite for Propane Dehydrogenation.

Crystalline zeolites have been proven to be excellent supports for confining subnanometric metal catalysts to boost the propane dehydrogenation (PDH) reaction. However, the introduced metallic species may suffer from severe sintering and limited stability during the catalytic process, especially when utilizing an industrial impregnation method for metal incorporation. In this study, we developed a new type of support based on amorphous protozeolite (PZ), taking advantage of its adjustable silanol chemistry and zeolitic microporous characteristic for stabilizing atomically dispersed PtSn catalyst via a simple, cost-effective coimpregnation process. The combination of X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy under CO atmosphere, and density functional theory calculations confirmed the formation of highly dispersed active Ptδ+-Ox-Sn species in PtSn/PZ. The PtSn/PZ catalyst exhibited a high propane conversion of 45.4% and a high propylene selectivity of 99% (WHSV= 3.6 h-1, 550 °C), with a high apparent rate coefficient of 565 molC3H6·gPt-1·h-1·bar-1 at a high WHSV of 108 h-1, presenting a top-level performance among the state-of-the-art Pt-based catalysts prepared by in situ synthesis and impregnation methods. The silanol density determined the chemical state of PtSn species, showing a change from atomically dispersed Ptδ+-Ox-Sn sites to PtSn alloy with decreasing silanol density of supports. This work provides a general strategy using silanol-rich amorphous protozeolite as support for stabilizing various metal catalysts by the simple impregnation method and also offers an effective way for fine tailoring the chemical state of metallic species via a silanol-engineered approach.

Breaking the stability limit of zeolite-based alkane dehydrogenation catalysts

Metal catalysts confined inside zeolite micropores or crystals are widely applied in the chemical industry because of their distinctive catalytic functions, especially with regard to the conversion of small and stable alkane molecules [1,2]. Silicalite-1 (S-1), a pure silica zeolite with an MFI topology, has a robust framework capable of withstanding harsh thermal and chemical conditions. Recently, S-1-based catalysts have demonstrated significant advantages in the construction and stabilization of various active metal centers and have attracted considerable attention for their potential in alkane dehydrogenation reactions. The absence of acidic sites prevents various acid-catalyzed side reactions, rendering S-1 a promising candidate for high-temperature reactions such as non-oxidative propane dehydrogenation (PDH). Sun et al. revealed that encapsulating subnanometer bimetallic PtZn clusters in S-1 resulted in a high propylene selectivity of 99%, with no catalyst deactivation even after 200h in the PDH reaction [3]. However, sustaining high stability at high conversion rates is still challenging for PDH reactions, and commercial processes are still based on Pt- and Cr-based catalysts, which need frequent regeneration.

Alumina lattice confined Niσ+ species as highly selective and anti-coking sites for sustainable propane dehydrogenation

Propane dehydrogenation (PDH) is a vital petrochemical process. As an alternative to Pt and Cr-based catalysts, Ni-based catalysts used in PDH, however, exhibit low propylene selectivity with severe coking. This work aims to understand the role of different Ni species in PDH and achieve high propylene selectivity by inhibiting coking. Specifically, we obtained NiOx/Al2O3 catalysts with solely tetrahedrally coordinated Ni2+ (NiIV) by selectively removing microcrystalline NiOx using the impregnation-complexation strategy. The Niσ+ species derived from NiIV exhibited high propylene selectivity (∼88 %) and low coke yield (2.26 %) in PDH. In contrast, reducing microcrystalline NiOx to Ni0 resulted in high methane selectivity and high coke yield (14.90 %). Theoretical calculations and experimental results indicate that this difference is attributed to the faster propylene desorption from Niσ+ as compared to that from Ni0. Therefore, catalysts with well-confined Niσ+ are selective in PDH. This study offers a rational strategy for designing Ni-based PDH catalysts.

Insights into Si/Al ratios for enhanced performance of β-zeolites in thermocatalytic cracking of crude oil to light olefins

The escalating demand for key petrochemicals, particularly ethylene and propylene, underscores the critical need for proficient catalysts in crude oil conversion processes. Attaining high propylene selectivity necessitates catalysts with superior adsorption capacity, thermal stability, moderate surface acidity, and pores large enough to facilitate the diffusion of larger crude oil molecules. In the present study, three different BEA Zeolites (β-zeolite) catalysts were successfully synthesized by hydrothermal method and used for catalytic cracking of Arabian Light crude oil to produce valuable petrochemical products, such as propylene, ethylene, and naphtha. The catalysts were characterized using 27Al and 29Si NMR, NH3-TPD, BET, XRD, TGA, FTIR, XRF, and FE-SEM. The thermocatalytic cracking of Arabian Light crude oil was evaluated in a fixed-bed microactivity test (MAT) unit between 550 and 600 °C. The as-prepared β-zeolite with a Si/Al ratio of 50 exhibited better catalytic activity in the catalytic cracking of Arabian Light crude oil compared to counterparts with Si/Al ratios of 35 and 65, This superiority can be attributed to its optimal combination of surface acid site distribution, textural properties, surface morphology, and high adsorption capacity. The highest feed conversion (83.4 %) and selectivity to propylene (16.11 %) were attained using β-zeolite with a Si/Al ratio of 50 at 600 °C. Importantly, our findings suggest that these catalysts hold significant potential, rivalling primary MFI catalysts like ZSM-5 commonly employed in similar reactions. This underscores their promise as catalysts of choice in the realm of catalytic cracking processes, paving the way for advancements in petrochemical production.

Disassembly-reassembly-phosphating strategy to fabricate hydrothermally-stable hierarchical P@ZSM-5 zeolite for efficient methanol-to-propylene

Available hierarchization and phosphorization of ZSM-5 zeolite as one of methanol-to-propylene (MTP) catalysts have improved reactive stability and propylene selectivity, but are subjected to the problems of poor phosphorus stabilization efficiency and inhomogeneous dispersion. Herein, we fabricate a series of hierarchical P@ZSM-5 zeolites via one-step disassembly-reassembly-phosphating strategy of ZSM-5 zeolite using successfully self-created asymmetric quaternary phosphonium hydroxides and elucidate the mechanism of mesoporous formation and the interaction of phosphorus with framework aluminum. Delightfully, reconstructively tetracoordinated PIV-O-AlIV structure endows excellent hydrothermal and Brønsted acid stability of hierarchical P@ZSM-5 zeolites. The MTP tests show that the P@ZSM-5(TBuCP) catalyst prepared by disassembly-reassembly-phosphating of tributylhexadecylphosphine hydroxide (TBuCPOH) exhibits superior propylene selectivity (48.9 %) and remarkedly long lifetime (32.5 h, WHSV=6h−1). Such enviable MTP performance is benefited from the join hands of the zeolitic hierarchization and suitable Brønsted acid strength conferred by its phosphorus-aluminum interaction that are conducive to olefinic cycle process. These findings afford value-filled opportunities in novel MTP catalysts with high reactive stability and propylene selectivity, and the understandings for phosphorus-zeolite chemistry.

γ-aminobutyric acid-assisted fabrication of plate-like ZSM-5 zeolite for efficient propylene production from methanol conversion

Plate-like ZSM-5 zeolites offering a short diffusion pathway along the b-axis are highly desirable catalyst for methanol to propylene (MTP) reaction. Herein, we successfully developed a simple synthetic strategy toward reducing the thickness along b-axis of ZSM-5 zeolite by combing a preliminary aging process and the addition of γ-aminobutyric acid. In particular, γ-aminobutyric acid adopted as a zeolite growth modifier was firstly proposed to prepare plate-like ZSM-5 zeolite with a short thickness of b-axis, and the minimum thickness can reach ∼50 nm. The shortened diffusion length in plate-like ZSM-5 zeolites could significantly improve the transport efficiency of molecules to and away from the active sites and finally leads to a better catalytic performance in the MTP reaction. Particularly, the plate-like ZSM-5 zeolite with an impressively shortened diffusion length (P-ZSM-5–0.3#0.3) displayed greatly improved catalytic performances (higher propylene selectivity and longer lifetime) than conventional ZSM-5 with a thicker dimension along the b-axis.

Synthesis of Ordered Mesoporous Molecular Sieve-Supported Cobalt Catalyst via Organometallic Complexation for Propane Non-Oxidative Dehydrogenation.

Co-based catalysts have shown great promise for propane dehydrogenation (PDH) reactions due to their merits of environmental friendliness and low cost. In this study, ordered mesoporous molecular sieve-supported CoOx species (CoOx/Al-SBA-15 catalyst) were prepared by one-step organometallic complexation. The catalysts show worm-like morphology with regular straight-through mesoporous pores and high external specific surface area. These typical features can substantially enhance the dispersion of CoOx species and mass transfer of reactants and products. Compared with the conventional impregnation method, the 10CSOC (10 wt.% Co/Al-SBA-15 prepared by the organometallic complexation method) sample presents a smaller CoOx size and higher Co2+/Co3+ ratio. When applied to PDH reaction, the 10CSOC delivers higher propane conversion and propylene selectivity. Under the optimal conditions (625 °C and 4500 h-1), 10CSOC achieves high propane conversion (43%) and propylene selectivity (83%). This is attributed to the smaller and better dispersion of CoOx nanoparticles, more suitable acid properties, and higher content of Co2+ species. This work paves the way for the rational design of high-performance catalysts for industrially important reactions.

Close Intimacy between PtIn Clusters and Zeolite Channels for Ultrastability toward Propane Dehydrogenation.

Propane dehydrogenation (PDH) serves as a pivotal intentional technique to produce propylene. The stability of PDH catalysts is generally restricted by the readsorption of propylene which can subsequently undergo side reactions for coke formation. Herein, we demonstrate an ultrastable PDH catalyst by encapsulating PtIn clusters within silicalite-1 which serves as an efficient promoter for olefin desorption. The mean lifetime of PtIn@S-1 (S-1, silicalite-1) was calculated as 37317 h with high propylene selectivity of >97% at 580 °C with a weight hourly space velocity (WHSV) of 4.7 h-1. With an ultrahigh WHSV of 1128 h-1, which pushed the catalyst away from the equilibrium conversion to 13.3%, PtIn@S-1 substantially outperformed other reported PDH catalysts in terms of mean lifetime (32058 h), reaction rates (3.42 molpropylene gcat-1 h-1 and 341.90 molpropylene gPt-1 h-1), and total turnover number (14387.30 kgpropylene gcat-1). The developed catalyst is likely to lead the way to scalable PDH applications.

Acid-leaching treated ZnO-based materials as highly efficient microwave catalysts for oxidative dehydrogenation of propane by CO2

The oxidative dehydrogenation of propane by CO2 (CO2-ODHP) reaction has received much attention for its potential to produce high-value propylene from two underutilized reactants and to eliminate CO2. However, it is a great challenge to maintain high propylene selectivity with high propane conversion for CO2-ODHP reaction, especially for non-expensive and environmentally friendly catalysts. Herein, a new and effective ZnO/S-1(1.0)-based microwave catalyst for CO2-ODHP was developed by a simple impregnation method and acid leaching treatment. Interestingly, the acid leaching treatment significantly enhanced the catalytic activity and stability. Importantly, both the conversion of propane and the selectivity of propylene were significantly enhanced in the microwave catalytic reaction mode (MCRM). An amazingly high conversion of ∼60 % and selectivity of ∼92 % is achieved. This method of significantly improving the catalytic activity and stability after a simple acid leaching treatment can provide some inspiration for light alkane dehydrogenation reactions.

Anchoring Pt sites via chemical confining functional ZnOx islands in propane dehydrogenation

The surface properties of heterogeneous catalysts regulated by the modified support are considered to be the key factors in determining catalytic performance. In propane dehydrogenation, PtZn catalysts have poor catalytic life due to the structural instability of Zn species although it owns high intrinsic activity. Herein, the dealuminated Beta zeolite is harnessed for chemically confining the introduced Zn species, the formed functionalZnOx (0 < x < 2) islands are further responsible for anchoring Pt1Zn1 alloys. According to the comprehensive characterization, the modifying surface defects on the Beta support can provide benign metal-support interaction and modulate the electronic structure of supported metal species. Hence, the Pt/ZnOx-SiBeta catalyst embodies 59.5 % propane conversion with a high propylene selectivity of 99.2 % and no obvious deactivation undergoing 100 h of dehydrogenation reaction. The optimal electronic interaction exists between ZnOx and SiBeta, which inhibits the aggregation of Pt sites and the coking formation.

Pt confined in Sn-ECNU-46 zeolite for efficient alkane dehydrogenation

Highly dispersed and stable Pt-based catalysts play a crucial role in constructing efficient catalytic systems for alkane dehydrogenation. In this study, a novel bimetallic Pt–Sn catalyst confined in extra-large-pore ECNU-46 zeolite (denoted as Pt/Sn-ECNU-46) is prepared by post-treatment. The open-site framework Sn species ((SiO)3Sn–OH) serve as anchors to interact with Pt species, favoring the high dispersion of Pt. On the other hand, the framework Sn species act as the second metal to regulate the geometrical and electronic environment of Pt species, thus suppressing their accumulation. Pt/Sn-ECNU-46 achieves a good performance in propane dehydrogenation reaction with high initial propane conversion (46%) and propylene selectivity (> 99%) as well as regeneration ability. In addition, Pt/Sn-ECNU-46 is also active in the dehydrogenation of n-hexane. This study explores the application of extra-large-pore zeolite as support in constructing metal-confined catalysts for alkane dehydrogenation.

Inside Cover Picture

Oxidative dehydrogenation of propane is attractive because of its exothermic nature but suffers from the over‐oxidation to CO and even CO2 as undesired by‐products. Ni single atoms supported on calcium aluminate are shown to be a potential candidate for propane oxidative dehydrogenation with higher propylene selectivity than that of Ni nanoparticles, which benefits from the positive chemical nature of single atoms. More details are discussed in the article by Qiao et al. on page 370—376.image

Photothermal oxidative dehydrogenation of propane to propylene over Cu/BN catalysts.

Oxidative dehydrogenation of propane (ODHP) is a reaction with significant practical significance. As for the industrial application of ODHP, it is challenging to achieve high activity and high propylene selectivity simultaneously. In this study, to overcome this obstacle, we designed a series of Cu/BN catalysts with unique morphologies for establishing a photothermal ODHP system with high efficiency and selectivity. Characterization and evaluation results revealed that Cu/BN-NS and Cu/BN-NF with enlarged specific surface areas exhibited higher catalytic activities. The localized surface plasmon resonance (LSPR) effect of Cu nanoparticles further enhanced the photothermal catalytic performances of Cu/BN catalysts under visible light irradiation. To the best of our knowledge, it is the first time to establish a BN-based photothermal ODHP catalytic system. This study is expected to pave pathways to realize high activity and propylene selectivity for the practical application of ODHP.

Alkaline-earth ion stabilized sub-nano-platinum tin clusters for propane dehydrogenation.

The strong promotion effects of alkali/alkaline earth metals are frequently reported for heterogeneous catalytic processes such as propane dehydrogenation (PDH), but their functioning principles remain elusive. This paper describes the effect of the addition of calcium (Ca) on reducing the deactivation rate of platinum-tin (Pt-Sn) catalyzed PDH from 0.04 h-1 to 0.0098 h-1 at 873 K under a WHSV of 16.5 h-1 of propane. The Pt-Sn-Ca catalyst shows a high propylene selectivity of >96% with a propylene production rate of 41 molC3H6 (gPt h)-1 and ∼1% activity loss after regeneration. The combination of characterization and DFT simulations reveals that Ca acts as a structural promoter favoring the transition of Snn+ in the parent catalyst to Sn0 during reduction, and the latter is an electron donor that increases the electron density of Pt. This greatly suppresses coke formation from deep dehydrogenation. Moreover, it was found that Ca promotes the formation of a highly reactive and sintering-resistant sub-nano Pt-Sn alloy with a diameter of approximately 0.8 nm. These lead to high activity and selectivity for the Pt-Sn-Ca catalyst for PDH.

Oxidative Dehydrogenation of Propane over Supported Nickel Single‐Atom Catalyst†

Comprehensive SummaryOxidative dehydrogenation of propane has been an ever‐growing field for propylene production due to its exothermic properties, of which overoxidation is the major drawback, with CO and even CO2 as undesired by‐products. For the purpose of getting higher propylene selectivity as well as yield, herein, we report Ni single atoms supported on calcium aluminate as an efficient catalyst candidate for propane oxidative dehydrogenation. Beneficial from higher valence states of Ni1 species, it shows 2—3 times as much propylene selectivity as that of Ni nanoparticles. About 14.2% C3H6 yield with 47.3% propylene selectivity has been achieved on Ni single atom catalyst and a good stability during 20 h test can be obtained as well.

Constructing Intrapenetrated Hierarchical Zeolites with Highly Complete Framework via Protozeolite Seeding.

Creation of intrapenetrated mesopores with open highway from external surface into the interior of zeolite crystals are highly desirable that can significantly improve the molecular transport and active sites accessibility of microporous zeolites to afford enhanced catalytic properties. Here, different from traditional zeolite-seeded methods that generally produced isolated mesopores in zeolites, nanosized amorphous protozeolites with embryo structure of zeolites were used as seeds for the construction of single-crystalline hierarchical ZSM-5 zeolites with intrapenetrated mesopores (mesopore volume of 0.51 cm3 g-1 ) and highly complete framework. In this strategy, in contrast to the conventional synthesis, only a small amount of organic structure directing agents and a low crystallization temperature were adopted to promise the protozeolites as the dominant growth directing sites to induce crystallization. The protozeolite nanoseeds provided abundant nucleation sites for surrounding precursors to be crystallized, followed by oriented coalescence of crystallites resulting in the formation of intrapenetrated mesopores. The as-prepared hierarchical ZSM-5 zeolites exhibited ultra-long lifetime of 443.9 hours and a high propylene selectivity of 47.92 % at a WHSV of 2 h-1 in the methanol-to-propylene reaction. This work provides a facile protozeolite-seeded strategy for the synthesis of intrapenetrated hierarchical zeolites that are highly effective for catalytic applications.