Catalysts For Dehydrogenation Research Articles

Extra-framework cations promoted zeolite-encaged cobalt catalysts towards efficient ethylbenzene dehydrogenation

The transformation of ethylbenzene to styrene through direct dehydrogenation is essential process in chemical industry, indispensable for the synthesis of polymers and plastics. Herein, faujasite zeolite encaged cobalt catalyst with potassium ion as the extraframework cations, namely K-Co@Y, is reported to be a robust catalyst for ethylbenzene direct dehydrogenation, showing ethylbenzene conversion of ∼45 % and styrene selectivity of ∼95 % simultaneously under employed conditions. The superior performance of K-Co@Y in comparison with Na-Co@Y is attributed to the effective modulation of zeolite-encaged Co2+ species by extraframework K+ ions, which increases the electron density of cobalt sites and facilitates CH bond activation. Although coke deposits cause gradual deactivation, the structural integrity of K-Co@Y can be well preserved during the dehydrogenation reaction and the performance can be full restored via a simple calcination regeneration step, making K-Co@Y an eligible catalyst for long-term running in the continuous regeneration mode. This study highlights the vital role of extraframework cations in zeolite-encaged single-site catalysts for target chemical transformations and opens up a new way to modulate the performance of zeolite catalysts.

Autothermal hydrogen release from liquid organic hydrogen carrier systems

A typical feature that the LOHC technology shares with other types of chemical hydrogen storage is that the release of hydrogen from the carrier requires an input of heat. In many use cases where waste heat from external sources is not available (e.g. in heavy-duty mobility), this is seen as a major drawback. In this paper, we show that autothermal LOHC dehydrogenation offers a very attractive way to overcome this drawback. In detail, we demonstrate autothermal hydrogen release from dicyclohexylmethane using diphenylmethane oxidation to benzophenone as source of heat. The full storage cycle involves benzophenone hydrodeoxygenation to dicyclohexylmethane, dicyclohexylmethane dehydrogenation to diphenylmethane, and diphenylmethane oxidation to benzophenone. We studied both the individual reaction steps using pure feedstocks and the integral cycle in which the intermediates and by-products of each reaction remain in the system for the subsequent reaction step. Although no efforts have yet been made to develop special catalyst materials for this purpose, the results with the applied commercial hydrodeoxygenation (Pd/C), dehydrogenation (Pt on alumina) and partial oxidation (VOx/TiO2) catalysts are already very promising. The storage cycle can be closed with high selectivity and with only minor total oxidation losses. The proposed concept of autothermal LOHC dehydrogenation offers the potential to increase the amount of useable hydrogen from a given amount of charged hydrogen carrier by up to 30%.

Facile and Environmentally Friendly Synthesis of Ga2O3/MFI Catalysts for Propane Dehydrogenation.

A GaOx-based catalyst is recognized as a promising catalyst for dehydrogenation of light alkanes. Conventionally, impregnation and calcination are necessary processes for the loading of GaOx. However, the incomplete impregnation of gallium salt solution would generate wastewater, and the calcination for the dissociation of gallium salt would release harmful gases, such as SOx, NOx, and HCl. Meanwhile, the high temperature results in an excessive energy cost and undesired GaOx particle aggregation. Here, we report a facile and environmentally friendly method for the synthesis of GaOx-based catalysts. The gallium salt solution was replaced directly with liquid gallium (LG). Through a simple physical mixing method at room temperature, uniform GaOx nanoparticles with diameters of around 3.5 nm were loaded onto the surface of silicalite-1 (S-1). With the optimal GaOx/MFI catalyst, the propane conversion and propylene selectivity reached 22.9 and 90.1%, respectively, in the propane dehydrogenation reaction. The work offers a clean and economical strategy utilizing liquid metal (LM) as an impregnation solution for the preparation of GaOx-based catalysts.

Production of CO-free H2 through aqueous formic acid dehydrogenation over the α-Mo2C/NC catalyst

Formic acid (FA) is considered a convenient hydrogen carrier with a high hydrogen-storage capacity. Although the non-noble-metal-based catalysts for FA dehydrogenation have made significant progress in recent years, they still face some challenges, such as complex preparation methods and inefficient FA dehydrogenation. Herein, a N-doped carbon (NC) supported α-Mo2C catalyst was successfully synthesized by the one-step pyrolysis strategy and performed excellent catalytic activity for neat FA decomposition while with a low dehydrogenation selectivity. The addition of water significantly improved the FA dehydrogenation selectivity and the α-Mo2C/NC catalyst showed a gas production rate of 224.19 mL/gcat./h and an almost complete dehydrogenation selectivity in the aqueous FA (40 vol.%) at 98 °C. Moreover, no significant deactivation was found during the 60 h stability test under different FA concentrations via this catalyst. The use of NC supported α-Mo2C obtained by one-step pyrolysis as an effective non-noble-metal catalyst and H2O introduction to promote selectivity could provide a novel low-cost­ H2 production strategy from FA.

Pd nanoparticles on DUT-67-PZDC-derived N-doped carbon for efficient H2 generation from formic acid dehydrogenation

It is important to develop heterogeneous catalysts with high efficiency and stability to catalyze formic acid (FA, HCOOH) dehydrogenation. Herein, through pyrolysis of DUT-67-PZDC and etching in a hydrofluoric acid (HF) solution, the HF-etched N-doped carbon (HNDC) carrier was obtained. Palladium nanoparticles (Pd NPs), with an average particle size of 3.0 nm, were prepared on the HNDC support using a simple chemical co-reduction method. The optimized Pd/HNDC catalyst demonstrates excellent catalytic activity, the initial turnover frequency (TOF) value is 6001 h−1 at 50 °C with the incorporation of sodium formate (SF) as an additive, and the FA conversion and hydrogen (H2) selectivity could be up to 100%, which is comparable to the majority of MOF-derived heterogeneous catalysts published to date. Additionally, the Pd/HNDC can maintain good stability in five consecutive FA dehydrogenation runs with only a slight decrease. Such remarkable catalytic performance of Pd/HNDC is mainly ascribed to the unique structure of HNDC support with high surface area and hierarchical pore characteristic, the strong synergistic interaction between Pd NPs and the N sites on HNDC, as well as the ultrasmall size and high dispersion of Pd NPs as the catalytic active site. This work offers an efficient method for assembling highly active catalysts for FA dehydrogenation.

Enhancement of ethylene selectivity in chemical looping oxidative dehydrogenation of ethane using manganese-based redox catalysts supported on HY zeolite

As the crucial role of zeolite catalysts becomes increasingly prominent in refining and petrochemical industries, this study introduces a novel application of xMn / HY catalysts in ethane catalytic dehydrogenation via Chemical Looping Oxidative Dehydrogenation (CL-ODH). The synergistic effect of manganese oxides on the HY framework and a moderate amount of acidic sites within the catalyst facilitates the cleavage of C-H bonds and the desorption of olefins, which are vital for advancing ethane CL-ODH. We identified the reasons for maintaining high ethylene selectivity using advanced characterization techniques such as XRD, SEM, TEM, BET, H2-TPR, NH3-TPD, and Py-IR. Notably, under optimized conditions at 700 °C with a gas time-space velocity (GHSV) of 1800 mL·h−1·g−1, the 3Mn/HY catalyst achieved approximately 97.1 % selectivity for ethylene and a 22.7 % conversion of ethane. These findings present a scalable route for ethylene production, showcasing significant industrial relevance by potentially reducing energy costs and improving yield.

Metal–Organic Skeleton-Derived W-Doped Ga2O3-NC Catalysts for Aerobic Oxidative Dehydrogenation of N-Heterocycles

N-heterocycles with quinoline structures hold significant importance within the chemical and pharmaceutical industries. However, achieving their efficient transformations remains a vital yet challenging endeavor. Herein, a series of W-doped Ga2O3-NC catalysts were synthesized using a Ga-MOF-derived strategy through a simple solvothermal method, with a remarkably high activity and selectivity towards the oxidative dehydrogenation of N-heterocycles. Furthermore, the MOF-derived W-doped Ga2O3-NC catalysts exhibit remarkable substrate tolerance and recyclability. The outstanding catalytic activity was attributed to the robust synergistic interaction between the W species and the Ga2O3-NC carrier, which facilitates the activation of hydrogen atoms in the C-H and C=N bonds on both the oxygen molecule and the substrate to produce H2O2. Additionally, the solvent effect of methanol can significantly enhance dehydrogenation due to its strong ability to donate and accept protons of hydrogen bonding. The present work provides a new approach to MOF-derived non-precious metal catalysts for achieving the efficient oxidation dehydrogenation of N-heterocycles.

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 in Science, Gong and coworkers 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.

CrMn‐based catalysts for oxidative dehydrogenation of propane to propylene with CO2

AbstractThe paper investigates the catalytic oxidative dehydrogenation of propane with carbon dioxide (ODH‐CO2) as a promising route for propylene production, an avenue yet to be commercially developed. Utilizing the incipient wetness catalyst preparation method, CrMn catalysts were synthesized on three supports (γ‐Al2O3, ZSM‐5, and SBA‐15). Comprehensive characterization through Brunauer–Emmett–Teller (BET) analysis, X‐ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM)‐energy‐dispersive X‐ray spectroscopy (EDS), and hydrogen temperature programmed reduction (H2‐TPR) was conducted to comprehend catalyst behaviour. Among the six catalysts tested, Cr/SBA‐15 was exhibited as the best performer, achieving propane and CO2 conversions of 36.2% and 14.1%, respectively, with a propylene selectivity of 33.4%. Over a 50‐h time on stream (TOS), it demonstrated gradual declines in conversions while retaining 75% of initial values. The incorporation of manganese as a promoter effectively mitigated coke formation, albeit with slight reductions in propane conversion and propylene selectivity.

Data-driven catalyst design for oxidative dehydrogenation of propane with CO2 using decision tree regression

Interpretable machine learning (ML) techniques have made significant progress in the design of high-performance materials. Here we employ decision tree (DT) models to discover and optimize multicomponent catalysts for the oxidative dehydrogenation of propane with CO2 (ODPC). While DT models have been used to improve a single target variable, this study leverages interpretable models by simultaneously considering the criteria for improving all the multiple target variables of ODPC, namely C3H8 conversion, CO2 conversion, and C3H6 yield. Instead of using literature data, we establish a consistent laboratory-scale database, and DT models are trained on multiple target variables representing catalytic performance. The trained DT models identify key input variables, including active metals, compositions, and support materials and provide criteria in the form of inequalities for the design of new ODPC catalysts. Despite using a database of binary and ternary metal oxides only, the fulfilment of all criteria suggests quaternary metal oxides with Cr, Ni, Mo, and ZrOx. The DT-proposed multicomponent catalysts show superior ODPC performance to the database catalysts, with a synergistic effect between the active elements. This exploitation of the relationship information between catalyst components and performance highlights the benefit of interpretable ML techniques in the design of high-performance multicomponent catalysts.

Propane Dehydrogenation on PtxZny Active Sites in Silicalite-1.

The improvement of Pt-based catalysts for propane dehydrogenation (PDH) has progressed by recent investigations that have identified Zn as a promising promoter for Pt subnanometer catalysts. It is desirable to gain insights into the structure, stability, and activity of such active sites and the factors that influence them, such as Zn:Pt ratio, Pt coordination and nuclearity. Here, we employ density functional theory and microkinetic simulations to investigate the stability of PtxZny (x=1-3, y=0-3) active sites grafted on silanols of Silicalite-1 and the PDH activity of Pt. We find that the coordination of a Pt atom to a nest of grafted Zn(II) atoms increases the stability of the Pt1Zny sites, whose activity is similar for y=0-2 and drops dramatically for y>2. We further demonstrate, via linear scaling relations and microkinetic simulations, that the turnover frequency obeys a volcano law as a function of propylene binding strength. The Pt2Zn1 and Pt3Zn1 sites are stable and exhibit activity similar to Pt1Zn2, but only Pt1Zn2 manifests reaction kinetics consistent with experimental data, strongly suggesting the active site composition in the synthesized catalyst samples. The methodology presented here suggests a general strategy for deducing active site information such as composition through simple kinetic experiments.

An Active and Regenerable Nanometric High‐Entropy Catalyst for Efficient Propane Dehydrogenation

AbstractPropane dehydrogenation (PDH) is crucial for propylene production, but commercially employed Pt‐based catalysts face susceptibility to deactivation due to the Pt sintering during reaction and regeneration steps. Here, we report a SiO2 supported nanometric (MnCoCuZnPt) high‐entropy PDH catalyst with high activity and stability. The catalyst exhibited a super high propane conversion of 56.6 % with 94 % selectivity of propylene at 600 °C. The propylene productivity reached 68.5 molC3H6 ⋅ gPt−1 ⋅ h−1, nearly three times that of Pt/SiO2 (23.5 molC3H6 ⋅ gPt−1 ⋅ h−1) under a weight hourly space velocity of 60 h−1. In a high‐entropy nanoparticle, Pt atoms were atomically dispersed through coordination with other metals and exhibited a positive charge, thereby showcasing remarkable catalytic activity. The high‐entropy effect contributes to the catalyst a superior stability with a low deactivation constant of 0.0004 h−1 during 200 hours of reaction under the industrial gas composition at 550 °C. Such high‐entropy PDH catalyst is easy regenerated through simple air combustion of deposited coke. After the fourth consecutive regeneration cycle, satisfactory catalytic stability was observed, and the element distribution of spent catalysts almost returned to their initial state, with no detectable Pt sintering. This work provides new insights into designing active, stable, and regenerable novel PDH catalysts.

Ga-doped spinel-typed Co-Al catalysts for CO2-assisted ethane dehydrogenation

A series of Ga-doped spinel-typed Co-Al catalysts were prepared via one-step evaporation-induced self-assembly (EISA) method. These catalysts present promising catalytic performance for CO2-assisted ethane dehydrogenation, which can be ascribed to the conjunction effect of cobalt and gallium species. The incorporation of Ga into the structure of Co-Al spinel has been recognized for enhancing CO2 conversion via reverse water-gas shift reaction, leading to a favorable equilibrium shift towards ethylene, along with an improved catalyst stability as a result of coexisting Boudouard reaction. Through X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), NH3 and CO2 temperature-programmed desorption (TPD) characterizations, coordinatively unsaturated Co2+ and Ga3+ cations were identified as collaborative catalytic active sites, with gallium species taking the prominent role. These sites were closely associated with the formation of acid-base pairs on the catalyst surface, which were crucial for the adsorption and activation of the reactants.

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.

Improving the Selectivity and Stability of Supported Cobalt Catalysts via Static Bi-Doping and Dynamic Trace CO2 Co-feeding during Propane Dehydrogenation.

Simultaneously enhancing selectivity and stability on supported propane dehydrogenation (PDH) catalysts remains a formidable challenge. Here, we report a combined static and dynamic strategy to address these issues synergistically. Firstly, we demonstrate a feasible sol-gel method for preparing atomically-dispersed Bi-decorated metal nanoparticle catalysts (MBi/Al2O3, M= Fe, Co, Ni, and Zn). In PDH testing, the total selectivity of by-products (CH4 and C2H6) significantly decreases to 4% for CoBi catalysts due to the static Bi-doping, compared with 16% for Co-supported catalysts. Secondly, to enhance catalytic stability, we introduce a dynamic trace CO2 co-feeding route. 10CoBi/Al2O3 catalysts exhibit superior durability against coke formation for 330 hours in PDH under a 40% C3H8 atmosphere followed by pure C3H8 conditions at 600 °C while maintaining propylene selectivity at 96%. Notably, introducing trace CO2 leads to a remarkable 6-fold decrease in the deactivation rate constant (kd). Multiple characterizations and density functional theory calculations reveal that charge transfer from atomically-distributed Bi to Co nanoparticles benefits lowering the energy of C3H6 adsorption thereby suppressing by-products. Furthermore, the dynamic co-feeding of trace CO2 facilitates coke removal, suppressing catalyst deactivation. The static Bi-doping and dynamic trace CO2 co-feeding strategy contributes simultaneously to increased selectivity and stability on supported PDH catalysts.

Improving the Selectivity and Stability of Supported Cobalt Catalysts via Static Bi‐Doping and Dynamic Trace CO2 Co‐feeding during Propane Dehydrogenation

Simultaneously enhancing selectivity and stability on supported propane dehydrogenation (PDH) catalysts remains a formidable challenge. Here, we report a combined static and dynamic strategy to address these issues synergistically. Firstly, we demonstrate a feasible sol‐gel method for preparing atomically‐dispersed Bi‐decorated metal nanoparticle catalysts (MBi/Al2O3, M= Fe, Co, Ni, and Zn). In PDH testing, the total selectivity of by‐products (CH4 and C2H6) significantly decreases to 4% for CoBi catalysts due to the static Bi‐doping, compared with 16% for Co‐supported catalysts. Secondly, to enhance catalytic stability, we introduce a dynamic trace CO2 co‐feeding route. 10CoBi/Al2O3 catalysts exhibit superior durability against coke formation for 330 hours in PDH under a 40% C3H8 atmosphere followed by pure C3H8 conditions at 600 °C while maintaining propylene selectivity at 96%. Notably, introducing trace CO2 leads to a remarkable 6‐fold decrease in the deactivation rate constant (kd). Multiple characterizations and density functional theory calculations reveal that charge transfer from atomically‐distributed Bi to Co nanoparticles benefits lowering the energy of C3H6 adsorption thereby suppressing by‐products. Furthermore, the dynamic co‐feeding of trace CO2 facilitates coke removal, suppressing catalyst deactivation. The static Bi‐doping and dynamic trace CO2 co‐feeding strategy contributes simultaneously to increased selectivity and stability on supported PDH catalysts.

Active and stable Ni-Cr oxide catalysts for oxidative dehydrogenation of ethane using CO2: Carbon cycle-assisted oxygen cycle

The CO2-assisted oxidative dehydrogenation of ethane (CO2-ODHE) is known as an ecologically beneficial process for ethylene generation and CO2 utilization. However, the quick deactivation of traditional Cr-based catalysts remains a considerable challenge. Herein, we report that a 1Ni1CrOx/ZrO2 catalyst could be high active and stable for the CO2-ODHE reaction; it showed CO2 conversion of 15.4 % and kept stable for 38 h at 600 °C, while the productivity of ethylene approached 325 μmol·min−1·gcat−1. Kinetic evaluations found a low apparent activation energy of 87.2 kJ/mol on the 1Ni1CrOx/ZrO2 catalyst. Surface Cr6+ and oxygen species were enriched to form Cr2O72− with the introduction of NiO. In addition, NiO improved the surface alkalinity and the affinity for oxygen, promoting the strong adsorption and easy activation of CO2. Importantly, Niδ+ species catalyzed the reaction between CO2 and surface-deposited carbon by redox cycling (carbon cycle), promoting Mars-van Krevelen-type carbon elimination and Cr6+ regeneration. The carbon cycle-assisted oxygen cycle on the Ni-Cr oxide catalysts could obviously enhance the carbon resistance and stable ethylene production, demonstrating potential application of Cr-based catalysts for CO2-ODHE reaction.

Cobalt-based Single-atom Dehydrogenation Catalysts Having High Selectivity and Regenerability and Method for Producing Corresponding Olefins from Paraffins Using the Same

Cobalt-based Single-atom Dehydrogenation Catalysts Having High Selectivity and Regenerability and Method for Producing Corresponding Olefins from Paraffins Using the Same

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.

New Clariant propane dehydrogenation catalyst improves selectivity

New Clariant propane dehydrogenation catalyst improves selectivity