C2 C4 Olefins Research Articles

Pd-Co Supported on Anodized Aluminium for VOCs Abatement: Reaction Mechanism, Kinetics and Applicability as Monolithic Catalyst

It has been found out that Pd-Co-based catalyst, supported on anodized aluminum, possesses very high activity in combustion reactions of C1–C6 alkanes and toluene. The catalyst characterization has been made by N2-pysisorption, XRD, SEM, XPS, FTIR, TEM, and EPR methods. In view of the great interest, methane combustion was investigated in detail. It is ascertained that the complete oxidation of methane proceeds by dissociative adsorption on PdO and formation of hydroxyl and methyl groups, the former being highly reactive, and it undergoes further reaction to oxygen-containing intermediates, whereupon HCHO is one of them. The presence of Co2+ cations promotes greatly oxygen adsorption. The dissociative adsorption is favored on neighboring Co2+ cations, leading to the formation of bridging peroxides. Further, the oxygen dissociates on the nearest Pd2+ cations. According to the results from the experimental data, instrumental methods, and the observed kinetics and DFT model calculations, it can be concluded that the reaction pathway over Pd+Co/anodic alumina support (AAS) catalyst proceeds most probably through Mars–van Krevelen. The obtained data on the kinetics were used for simulation of the methane combustion in a full-scale adiabatic reactor.

Efficient conversion of syngas to linear α-olefins by phase-pure χ-Fe5C2.

Oil has long been the dominant feedstock for producing fuels and chemicals, but coal, natural gas and biomass are increasingly explored alternatives1-3. Their conversion first generates syngas, a mixture of CO and H2, which is then processed further using Fischer-Tropsch (FT) chemistry. However, although commercial FT technology for fuel production is established, using it to access valuable chemicals remains challenging. A case in point is linear α-olefins (LAOs), which are important chemical intermediates obtained by ethylene oligomerization at present4-8. The commercial high-temperature FT process and the FT-to-olefin process under development at present both convert syngas directly to LAOs, but also generate much CO2 waste that leads to a low carbon utilization efficiency9-14. The efficiency is further compromised by substantially fewer of the converted carbon atoms ending up as valuable C5-C10 LAOs than are found in the C2-C4 olefins that dominate the product mixtures9-14. Here we show that the use of the original phase-pure χ-iron carbide can minimize these syngas conversion problems: tailored and optimized for the process of FT to LAOs, this catalyst exhibits an activity at 290 °C that is 1-2 orders higher than dedicated FT-to-olefin catalysts can achieve above 320 °C (refs. 12-15), is stable for 200 h, and produces desired C2-C10 LAOs and unwanted CO2 with carbon-based selectivities of 51% and 9% under industrially relevant conditions. This higher catalytic performance, persisting over a wide temperature range (250-320 °C), demonstrates the potential of the system for developing a practically relevant technology.

Insight into the synthesis of alkali metal modified Co-doped ZnFe2O4 with faveolate spinel structure and their enhanced selectivity of olefins during CO2 hydrogenation

Emission reduction of CO2 allows of no delay, and CO2 hydrogenation strategy reveals the great potential to achieve target of “Carbon Neutral”. Trapped with the low selectivity of olefins in our previous work of Co-doped ZnFe2O4, the alkali metal (Na, K) modified Co-doped ZnFe2O4 were synthesized, and their enhanced selectivity of olefins were present. The promotion caused by alkali metal modification revealed that more generation of metallic Fe and the additional generation of Fe5C2 species could be ascribed for the enhanced selectivity of C2-C4 olefins and C5+ products. The introduced alkali metal via the strong electronic interaction increased the outer electrons density around Fe atoms, which could promote the adsorption of CO2 and prohibited the secondary hydrogenation reaction of the formed olefins. Therefore, the enhanced selectivity of C2-C4 olefins over the alkali metal (Na, K) modified Co-doped ZnFe2O4 was emerged, while the CO2 conversion was suppressed (caused by the less generation of Fe3O4). Compared with Na-modified samples, the introduced K could make more generation of Fe5C2 to promote the carbon chain growth, due to its stronger alkalinity, thus leading to the highest selectivity of C5+ products over K-modified samples while the highest selectivity of C2-C4 olefins over Na-modified samples.

Photoredox Oxidation of Alkanes by Monometallic Copper-Oxygen Complexes Using Visible Light Including One Sun Illumination.

Oxygenation of hydrocarbons offers versatile catalytic routes to more valuable compounds, such as alcohols, aldehydes, and ketones. Despite the importance of monometallic copper-oxygen species as hydroxylating agents in biology, few synthetic model compounds are known to react with hydrocarbons, owing to high C-H bond dissociation energies. To overcome this challenge, the photoredox chemistry of monometallic copper (pyrazolyl)borate complexes coordinated by chlorate has been explored in the presence of C1-C6 alkanes with BDEs ≥ 93 kcal/mol. Ethane is photooxidized at room temperature under N2 with yields of 15-30%, which increases to 77% for the most oxidizing tris(3,5-trifluoromethyl-pyrazolyl)borate complex (Cu-3). This complex also promotes the photooxidation of methane to methanol in significant yield (38%) when the photoredox reaction is run under aerobic conditions. Ligand modification alters the reaction selectivity by tuning the redox potential. The ability to activate 1° C-H bonds of C1-C6 alkanes using visible light is consistent with the photogeneration of a powerfully oxidizing copper-oxyl, which is supported by photocrystallographic studies of the tris(3,4,5-tribromopyrazolyl)borate chlorate complex. Mechanistic studies are consistent with the hydrogen atom abstraction of the C-H bond by the copper-oxyl intermediate. We demonstrate for Cu-3 with hexane as an exemplar, that the photoredox chemistry may be achieved under solar conditions of one-sun illumination.

Electronic and geometric features controlling the reactivity of Mg-vanadate and V2O5 surfaces toward the initial C–H activation of C1–C3 alkanes – A DFT+U study

This work employs density functional theory (DFT+U) calculations to explore initial C–H activations in C1–C3 alkanes on V2O5, MgV2O6 (meta-vanadate), Mg2V2O7 (pyro-vanadate), and Mg3V2O8 (ortho-vanadate) surfaces. These materials are selective catalysts for the oxidative dehydrogenation (ODH) of alkanes into alkenes, which offers practical and thermodynamic advantages over non-oxidative alkane dehydrogenation. The geometric and electronic properties that govern the reactivity of these materials, however, have not been explored by theory despite their importance in controlling rate determining alkane initial C–H activation during ODH catalysis. In this work, we explore fourteen low-energy surfaces of MgxV2Ox+5 (x = 0–3) exposing 64 distinct O atoms (reaction sites). C–H activation barriers are largest on Mg3V2O8, lower and similar for Mg2V2O7 and MgV2O6, and lowest for V2O5 surfaces; these predicted trends are consistent with measured ODH reactivity in earlier studies. Barriers are lowest (on average) when alkanes react with O atoms bound to a single V atom, with bridging O atoms having slightly higher barriers, and three-fold O atoms having the largest activation barriers. However, there is scattering within each subset indicating that factors beyond O-atom coordination have a significant role in the barriers. Vacancy formation energies (VFE) and the O 2p band energies were found to be weak descriptors of surface O reactivity for alkane activation barriers. Hydrogen addition energy (HAE) and methyl addition energy (MAE) values, in contrast, were found to correlate well with alkane activation barriers. MAE, however, outperforms HAE correlations because of the tendency of H* to form H-bonds with nearby surface O atoms, and those H-bonds are absent in C–H activation transition states causing scatter in the correlation of barriers with HAE. Constrained-orbital DFT methods were used to establish a theoretical thermochemical cycle that decouples surface reduction by CH3* into three components: surface distortion, orbital localization, and bond formation. These results give insights into how Mg:V ratios, surface structure (O-atom coordination), and reducibility (HAE, MAE) impact the reactivity of vanadium-based metal oxides toward alkane activation.

Methyl mercaptan-to-hydrocarbons: Effect of topology of zeolite catalysts

The conversion of methyl mercaptan was examined over zeolites with MFI, FAU, BEA, MOR, CHA and MWW topology and Si/Al ratio between 10 and 19. At 450 °C, over all catalysts, the reagent has been primarily consumed into hydrocarbons and H2S. The crucial variables affecting the hydrocarbon distribution over zeolites were mainly their pore size/architecture and the amount of the acid sites. Over 3D H-ZSM-5, H-β and H-MOR zeolite, many aromatics and only few olefins were produced. In contrast, and analogous to methanol-to-hydrocarbons process, H-SSZ-13 and H-MCM-22 zeolite (containing cages and small pores) mainly produced C2-C3 olefins.

H-atom abstraction reactions of C1-C4 alkanes by ketenyl radical: Kinetic investigation and analysis

The kinetics of 16 H-atom abstraction reactions of C1-C4 alkanes by ketenyl radical (HCCO) are studied to enhance the existing combustion mechanisms. Firstly, the obtain the lowest-energy conformer, vibration frequencies and single point energies for the reactants, prepolymers, transition states, and products are determined using the CCSD(T)/cc-pVQZ//B3LYP/6-311G+(d,p) theory level. Subsequently, temperature-dependent reaction rate constants for the major channels are predicted by the TST method. Finally, the H-atom abstraction reactions are validated under multiple temperature conditions, and the effects of the reactions on auto-ignition process and CO emission characteristics of n-heptane/NG mixture are researched. The results indicate that the H-atom abstraction reactions by Cα-atom play a significant role for the diesel/NG combustion. To combine the reaction pathways and rate constants into the existing kinetic mechanisms resulted in more accurate predictions of the ignition delay time. Furthermore, these kinetics data are valuable for revealing the CO emissions of the dual-fuel engines.

STUDYING THE INFLUENCE OF ALKALINE TREATMENT AND MODIFICATION OF ZEOLITE ON ITS PHYSICAL-CHEMICAL AND CATALYTIC PROPERTIES IN THE PROCESS OF PROPANE CONVERSION TO OLEFIN HYDROCARBONS

In this work, the effect of alkaline treatment of ZSM-5 zeolite with a modulus of 100 on its physicochemical properties and activity in the process of converting propane into olefin hydrocarbons was investigated. The growing demand for lower olefins is driving the search for new ways to improve existing technologies and develop new, more efficient catalysts. Catalytic dehydrogenation of light alkanes is an alternative to the petrochemical method for producing lower olefins from cheap and available gas and oil and gas feedstocks. At the same time, dehydrogenation reactions of light alkanes have a number of features and limitations that determine the range of possible catalysts. Zeolites are a class of supports that, due to their large surface area, nanometer-sized pores, and good thermal stability, can be used to prepare catalysts for the dehydrogenation of C2−C4 alkanes. An important feature of crystalline high-silica zeolites is the ability to change their acidic properties under the influence of various pre-treatments, which opens up great opportunities for their regulation and, accordingly, the selection of the most effective catalyst for a particular chemical process. It has been shown that alkaline treatment of zeolite leads to the formation of an additional amount of mesopores, which, in turn, affects its catalytic properties in the process of converting propane into olefinic hydrocarbons. The dependence of the activity and selectivity of the zeolite catalyst on the concentration of the alkali solution used for its treatment has been established. It was found that treatment of the zeolite catalyst with a 1.0 M NaOH solution leads to an increase in its selectivity with respect to the formation of C2–C4 olefins from propane, which at a process temperature of 650 °C reaches 32.0% with a propane conversion of 81%. It has been shown that additional promotion of desilicated zeolite with magnesium or manganese increases its activity with respect to the formation of olefinic hydrocarbons from propane. For citation: Vosmerikov A.A., Vosmerikova L.N., Vosmerikov A.V. Studying the influence of alkaline treatment and modification of zeolite on its physical-chemical and catalytic properties in the process of propane conversion to olefin hydrocarbons. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 8. P. 50-58. DOI: 10.6060/ivkkt.20246708.11t.

Experimental Reactivity of (MoO3)NO- (N = 1-21) Cluster Anions with C1-C4 Alkanes: A Simple Model to Predict the Reactivity with Methane.

Metal oxide clusters with atomic oxygen radical anions are important model systems to study the mechanisms of activating and transforming very stable alkane molecules under ambient conditions. It is extremely challenging to characterize the activation and conversion of methane, the most stable alkane molecule, by metal oxide cluster anions due to the low reactivity of the anionic species. In this study, using a ship-lock type reactor that could be run at relatively high pressure conditions to provide a high number of collisions in ion-molecule reactions, the rate constants of the reactions between (MoO3)NO- (N = 1-21) cluster anions and the light alkanes (C1-C4) were measured under thermal collision conditions. The relationships among the reaction rates of different alkanes were obtained to establish a model to predict the low rate constants with methane from the high rate constants with C2-C4 alkanes. The model was tested by using available experimental results in literature. This study provides a new method to estimate the relatively low reactivity of atomic oxygen radical anions with methane on metal oxide clusters.

Effect of pretreatment conditions on a benchmark iron catalyst for CO2 hydrogenation to light olefins

To improve the CO2-to-light olefin process in terms of economics, efficient catalysts are essential to maximize the yield. Our research was carried out on FeAlCuK, which is still considered as a benchmark for olefin formation via CO2 Fischer-Tropsch synthesis (FTS). Nevertheless, the effect of various activation conditions on the formation of desired active species and final activity of this catalyst has not been described in literature to date. We studied the pretreatment by varying both the reduction gas and temperature. The catalyst was pretreated with pure H2 or synthesis gas (H2/CO = 3) to identify the bulk and surface species formed in each case. We demonstrate that the FeCuAlK catalyst should be activated in a H2/CO atmosphere at 250 °C for 4 h before the test at typical FTS reaction conditions to reach maximum productivity. The reduction with H2/CO led to the formation of active Fe5C2 and Fe3O4 phases producing a high fraction of light olefins at higher CO2 conversion. The role of promoters K and Cu was also investigated. Selectivity for desired C2-C4 olefins increased by 10 % compared to catalysts which were used directly in FTS without preliminary activation. Characterization with ex and in situ powder X-ray diffraction, Raman spectroscopy, and XPS after each activation treatment as well as Mössbauer spectroscopy revealed a strong impact of gas nature on the phase composition which was correlated with the performance.

Deactivation of an Fe-based catalyst in the dehydrogenation of light alkanes under H2S co-feeding: A case study

The effectiveness of a Ru-Fe/SiO2 catalyst, which exhibits excellent propane dehydrogenation with H2S co-feeding, was verified for the dehydrogenation of various lower alkanes. When the dehydrogenation characteristics of C2–C4 alkanes were evaluated under H2S co-feeding, the Ru-Fe/SiO2 catalyst exhibited a high dehydrogenation activity in all cases. However, a significant degradation tendency of the catalyst was observed when lighter alkanes with smaller carbon numbers were used as the feedstock. The deposition of coke (carbon) and solid sulfur and the reduction of Fe species were identified as the main factors responsible for catalyst degradation. To further evaluate the factors affecting catalyst degradation, the effect of co-feeding H2 with the gas feedstock on the catalyst performance was investigated. The reaction stability improved significantly with the co-feeding of H2 during ethane and propane dehydrogenation reactions. This outcome is attributed to the smooth reduction and removal of the carbon accumulated on the catalyst surface, which is the main cause of catalyst degradation.

Modification of ZSM-23 zeolite via vapor-phase transport method: Reducing the length along the unidimensional channels for enhanced catalytic performances in methanol-to-hydrocarbons

ZSM-23, a unidimensional zeolite, finds application in the methanol-to-hydrocarbons (MTH) reaction, but commonly suffers from rapid deactivation due to diffusion hindrances. Given the challenges of reducing the length along the a-axis of ZSM-23 zeolite while preserving its catalytic functions using conventional methods, this study introduces a post-modification approach inspired by the vapor-phase transport (VPT) method, wherein ZSM-23 is subjected to the vapor of an iso-propylamine (IPA) solution. The results demonstrated that the crystal lengths aligned with the micropores can be effectively reduced to less than half of the original material (115 nm vs. 289 nm), while preserving much of the microstructure and acidity. Insights into the post-treatment mechanism unveiled a coexistence of etching and re-crystallization processes during the procedure, with conditions finely adjustable by varying the concentrations of the IPA solution. The optimized modification procedure resulted in ZSM-23 zeolite demonstrating an increased C2–C4 olefin yield (62.2 % vs. 53.2 %) and enhanced stability (22 h vs. 5 h) in MTH reaction compared to the untreated sample, which can be attributed to the enhanced diffusion properties of the modified zeolite. This vapor-assisted modification protocol successfully expands the toolkit for synthesizing efficient one-dimensional zeolite for catalytic purposes.

Theoretical Investigation on the H Atom Abstraction Reaction from C1-C4 Alkanes and Alkenes by ṄH2 Radicals.

The H atom abstraction reactions from alkanes and alkenes by ṄH2 are decisive in predicting the combustion characteristics of NH3/CxHy binary fuels. Theoretical investigation is carried out on the energy barriers of H atom abstraction reactions from C1-C4 alkanes/alkenes by ṄH2 radicals at the QCISD(T)/CBS//M06-2X/6-311++G(d,p) level of theory. Single-point energies of each species are computed using QCISD(T)/cc-pVDZ, TZ level of theories with basis set corrections from MP2/cc-pVDZ, TZ, and QZ methods. One-dimensional hindered rotor potentials are obtained by the M06-2X/cc-pVTZ method with 10° increment. Rate constants of each channel across temperatures of 298.15-2000 K are calculated by solving the RRKM/Master Equation with conventional transition state theory. For alkanes, rate constants order follows ktertiary> ksecondary> kprimary, while for alkenes the order follows kallylic> kprimary> kvinylic. Among the vinylic carbon sites within the same alkene species, the hydrogen atom sharing the same carbon with the allylic carbon on the C-C double bond is the preferred site for the H atom abstraction reaction. The branching ratio results indicate that the abstraction from tertiary or secondary carbon sites on alkanes and allylic carbon sites on alkenes are dominating during the investigated temperature range but become less important as the temperature increases. The data provided in this work are in good agreement with the literature data, but for the ṄH2+alkenes system, the literature data are scarce and further investigation is needed.

Well-Defined Supported ZnOx Species: Synthesis, Structure, and Catalytic Performance in Nonoxidative Dehydrogenation of C3-C4 Alkanes.

ConspectusZinc oxide (ZnO) is a multipurpose material and finds its applications in various fields such as rubber manufacturing, medicine, food additives, electronics, etc. It has also been intensively studied in photocatalysis due to its wide band gap and environmental compatibility. Recently, heterogeneous catalysts with supported ZnOx species have attracted more and more attention for the dehydrogenation of propane (PDH) and isobutane (iBDH) present in shale/natural gas. The olefins formed in these reactions are key building blocks of the chemical industry. These reactions are also of academic importance for understanding the fundamentals of the selective activation of C-H bonds. Differently structured ZnOx species supported on zeolites, SiO2, and Al2O3 have been reported to be active for nonoxidative dehydrogenation reactions. However, the structure-activity-selectivity relationships for these catalysts remain elusive. The main difficulty stems from the preparation of catalysts containing only one kind of well-defined ZnOx species.In this Account, we describe the studies on PDH and iBDH over differently structured ZnOx species and highlight our approaches to develop catalysts with controllable ZnOx speciation relevant to their performance. Several methods, including (i) the in situ reaction of gas-phase metallic Zn atoms with OH groups on the surface of supports, (ii) one-pot hydrothermal synthesis, and (iii) impregnation/anchoring methods, have been developed/used for the tailored preparation of supported ZnOx species. The first method allows precise control of the molecular structure of ZnOx through the nature of the defective OH groups on the supports. Using this method, a series of ZnOx species ranging from isolated, binuclear to nanosized ZnOx have been successfully generated on different SiO2-based or ZrO2-based supports as demonstrated by complementary ex/in situ characterization techniques. Based on kinetic studies and detailed characterization results, the intrinsic activity (Zn-related turnover frequency) of ZnOx was found to depend on its speciation. It increases with an increasing number of Zn atoms in a ZnmOn cluster from 1 to a few atoms (less than 10) and then decreases strongly for ZnOx nanoparticles. The latter promote the formation of undesired C1-C2 hydrocarbons and coke, resulting in lower propene selectivity in comparison with the catalysts containing only ZnOx species ranging from isolated to subnanometer ZnmOn clusters. In addition, the strategy for improving the thermal stability of ZnOx species and the consequences of mass-transport limitations for DH reactions were also elucidated. The results obtained allowed us to establish the fundamentals for the targeted preparation of well-structured ZnOx species and the relationships between their structures and the DH performance. This knowledge may inspire further studies in the field of C-H bond activation and other reactions, in which ZnOx species act as catalytically active sites or promoters, such as the dehydroaromatization of light alkanes and the hydrogenation of CO2 to methanol.

Mesoporous Co@MCM-41 catalyst for stable ethane dehydrogenation

Catalytic dehydrogenation of low-cost C2-C4 alkanes can be an alternative route to produce value-added olefins. To overcome the drawback of a microporous Co-based Co@MFI zeolite catalyst that is sensitive to coke deposition for its deactivation, herein, a mesoporous Co-incorporated MCM-41 catalyst was synthesized by hydrothermal synthesis successfully and tested for ethane dehydrogenation. Various characterizations suggested that Co species were also dispersed in an atomical level in the MCM-41 zeolite with a reduction-resistant –Coδ+–Oδ-– structure, which, therefore, ensures its high selectivity to ethylene (∼100 %). Thanks to the mesoporous characteristic of the MCM-41, the as-synthesized Co@MCM-41 catalyst showed excellent stability than the widely reported microporous Co@MFI catalysts, which can be attributed to the reason that the mesoporous channels are not sensitive to coke deposition and still allow reactant and products to diffuse in and out easily, This work demonstrates the importance of the diffusion of a zeolite-based catalyst and promotes the application of Co-based catalyst for alkane dehydrogenation.

Investigation of AFeO3 (A=Ba, Sr) Perovskites for the Oxidative Dehydrogenation of Light Alkanes under Chemical Looping Conditions.

Oxidative dehydrogenation (ODH) of light alkanes to produce C2-C3 olefins is a promising alternative to conventional steam cracking. Perovskite oxides are emerging as efficient catalysts for this process due to their unique properties such as high oxygen storage capacity (OSC), reversible redox behavior, and tunability. Here, we explore AFeO3 (A=Ba, Sr) bulk perovskites for the ODH of ethane and propane under chemical looping conditions (CL-ODH). The higher OSC and oxygen mobility of SrFeO3 perovskite contributed to its higher activity but lower olefin selectivity than its Ba counterpart. However, SrFeO3 perovskite is superior in terms of cyclic stability over multiple redox cycles. Transformations of the perovskite to reduced phases including brownmillerite A2Fe2O5 were identified by X-ray diffraction (XRD) as a cause of performance degradation, which was fully reversible upon air regeneration. A pre-desorption step was utilized to selectively tune the amount of lattice oxygen as a function of temperature and dwell time to enhance olefin selectivity while suppressing CO2 formation from the deep oxidation of propane. Overall, SrFeO3 exhibits promising potential for the CL-ODH of light alkanes, and optimization through surface and structural modifications may further engineer well-regulated lattice oxygen for maximizing olefin yield.

Synergistic enhancement of CO2 hydrogenation to C5+ hydrocarbons using mixed Fe5C2 and Na-Fe3O4 catalysts: Effects of oxide/carbide ratio, proximity, and reduction

CO2 hydrogenation into sustainable chemical feedstocks and fuels is a pivotal focus of energy research. Fe-based catalysts have emerged as promising candidates due to their high efficiency in the CO2 hydrogenation toward C2–C4 olefins and C5+ hydrocarbons. Fe5C2 is known as the active phase of the CO2 hydrogenation. Therefore, it is imperative to discern the roles of active phases in product distribution. Accordingly, in the present study, Fe5C2 is synthesized separately and physically mixed with Na-Fe3O4. The effects of oxide/carbide ratio, the proximity of active phases, and reduction treatment are investigated. The results show that adding carbide to oxide in an appropriate ratio significantly increases CO2 conversion due to the controlled reduction of the oxide phase and enhanced CO2 adsorption. Additionally, a closer distance (mixed-powder pellets) between Na-Fe3O4 and Fe5C2 results in higher selectivity for C2-C4 olefins and C5+ hydrocarbons and less CH4. Furthermore, the graphitized layers of reduced catalyst (R-Na-Fe3O4/Fe5C2 (70/30 wt%)) enhance the selectivity to C2-C4 olefins (40 %) and C5+ hydrocarbons (35 %) at around 40 % CO2 conversion. In contrast, amorphous carbon in the non-reduced catalyst (NR-Na-Fe3O4/Fe5C2 (70/30 wt%)) favors more C2-C4 paraffins and CH4. Therefore, the interplay between the influential factors, i.e., oxide/carbide ratio, spatial distance, and reduction treatment, can result in tailoring an efficient CO2 hydrogenation catalyst toward the formation of valuable hydrocarbons.

Regulating framework aluminum location towards boosted light olefins generation in ex-situ catalytic pyrolysis of low-density polyethylene

Amidst the global focus on recycling and treatment of waste plastics for resource sustainability, it remains an enormous challenge to convert waste plastics into light olefin. Herein, the impact of framework Al (AlF) location in ZSM-5 catalyst, controlled by regulating Al sources, on the ex-situ catalytic pyrolysis of low-density polyethylene (LDPE) has been investigated. Based on multi-techniques, such as 27Al MAS NMR, ICP-AES, Co-UV–vis-DRS, XRD, SEM, N2 adsorption-desorption, NH3-TPD, Py-IR and FTIR. It is found that the AlF located at the channel intersections show more Al pairs, and this location offers ample space for secondary reactions, which include Diels-Alder reaction, cyclization reaction and dehydrogenation reaction, resulting in the low yield of light olefins (10.6 wt%) and the generation of light alkanes and aromatics from light olefins. In contrast, AlF located in the straight and sinusoidal channels exists mainly in the form of single Al. The substantial steric hindrance for this location facilitates the cracking reaction, mainly referring to the cracking reactions of LDPE that produce light olefins and generate enhanced yield of light olefins (52.8 wt%). These results provide new perspectives towarding boosted light olefins generation in ex-situ catalytic pyrolysis of LDPE.

Interaction-selective molecular sieving adsorbent for direct separation of ethylene from senary C2-C4 olefin/paraffin mixture

Olefin/paraffin separations are among the most energy-intensive processes in the petrochemical industry, with ethylene being the most widely consumed chemical feedstock. Adsorptive separation utilizing molecular sieving adsorbents can optimize energy efficiency, whereas the size-exclusive mechanism alone cannot achieve multiple olefin/paraffin sieving in a single adsorbent. Herein, an unprecedented sieving adsorbent, BFFOUR-Cu-dpds (BFFOUR = BF4-, dpds = 4,4’-bipyridinedisulfide), is reported for simultaneous sieving of C2-C4 olefins from their corresponding paraffins. The interlayer spaces can be selectively opened through stronger guest-host interactions induced by unsaturated C = C bonds in olefins, as opposed to saturated paraffins. In equimolar six-component breakthrough experiments (C2H4/C2H6/C3H6/C3H8/n-C4H8/n-C4H10), BFFOUR-Cu-dpds can simultaneously divide olefins from paraffins in the first column, while high-purity ethylene ( > 99.99%) can be directly obtained through the subsequent column using granular porous carbons. Moreover, gas-loaded single-crystal analysis, in-situ infrared spectroscopy measurements, and computational simulations demonstrate the accommodation patterns, interaction bonds, and energy pathways for olefin/paraffin separations.

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.