Direct Dehydrogenation Research Articles

Potassium-promoted single-atom Co-N-C catalyst for direct dehydrogenation of ethylbenzene

Potassium-promoted single-atom Co-N-C catalyst for direct dehydrogenation of ethylbenzene

Surface engineering of Pt surfaces with Au and cobalt oxide nanostructures for enhanced formic acid electro-oxidation

A novel n-CoOx/n-Au/n-Pt nanocatalyst assembled onto a glassy carbon (GC) substrate is recommended for efficient formic acid electro-oxidation (FAEO), the principal anodic reaction in the direct formic acid fuel cells (DFAFCs). • A catalyst composed of Pt nanoparticles was engineered with Au and cobalt oxide nanostructures. • It showed a promising catalytic performance toward the formic acid electro-oxidation. • Adjusting its loading hierarchy drove the reaction mechanism to the desirable dehydrogenation pathway. • Geometric and electronic enhancements were elucidated and quantified. This study aims to mitigate the CO poisoning of platinum (Pt) surfaces during formic acid electro-oxidation (FAEO), the essential anodic reaction in the direct formic acid fuel cells (DFAFCs). For this purpose, a glassy carbon (GC) electrode was amended sequentially with Pt (n-Pt), gold (n-Au), and cobalt oxide (n-CoOx) nanostructures. Fascinatingly, the ternary modified n-CoOx/n-Au/n-Pt/GC catalyst (for which n-Pt, n-Au, and n-CoOx were sequentially and respectively assembled onto the GC surface) exhibited a remarkable electrocatalytic enhancement toward FAEO, which surpassed ca. 53 times that of the Pt/GC catalyst. Additionally, it exhibited a much (ca. 18 times) higher stability after 3000 s of continuous electrolysis. The observed enhancement was proven to originate from driving the reaction mechanism principally to the desirable direct dehydrogenation pathway on the expense of the poisoning dehydration path. The impedance and CO stripping measurements confirmed the prevailing of both the electronic and third body effects in the catalytic enhancement.

Enhancing propane direct dehydrogenation performances through temperature induced VOx dispersion and alumina support phase transformation

Vanadium oxide-based catalysts are promising candidates for propane direct dehydrogenation. A strategy was developed in the present study to enhance the intrinsic activity and coking-resistance of supported VOx catalysts at the same time. The annealing temperature and VOx surface density were identified as regulation parameters to tailor the dispersion of VOx and micro-environment of V-O-Al active sites. The surface acidic VOx was found capable of inducing local structure rearrangement of transition alumina and the transformation of amorphous δ- to more crystalline θ-alumina at relatively lower temperatures, contributing to lowering VOx-support interactions and enhancing VOx reducibility. The DFT calculations verify that the chemical states of V-O active sites could be tuned by the ligand Al3+ coordination micro-environment, and the octahedral Al3+ serving as ligands contributes to enhancing the reducibility and C–H bond rupture capability of V-O site. The annealing temperature was also found capable of dispersing VOx species over alumina surface with the optimal temperature dependent of specific VOx loadings. As a consequence, the intrinsic activity of 3.1 V/Al2O3-900 and the deactivation rate of 3.1 V/Al2O3-700 with dominantly isolated VOx is 1.4 times and 0.65 times that of 3.1 V/Al2O3-550, respectively.

Effects of second metals (M = Fe, Cu, Ga, In, Sn) on the geometric and electronic properties of platinum for the direct dehydrogenation of propane

Supported Pt-based bimetallic catalysts are representative types of dehydrogenation catalysts used for alkanes to olefins conversion. The platinum in these catalysts exhibits unique structural features accompanied with changes in electronic states due to the addition of the second metal. To investigate the impact of each effect on the activity for propane dehydrogenation, a series of Pt-M/SiO 2 (M= Fe, Cu, Ga, In and Sn) catalysts were prepared and used for propane dehydrogenation. Utilizing various characterization techniques, the geometric and electronic properties of these catalysts were studied. The relationships between the specific activity of bimetallic platinum catalysts in propane dehydrogenation and atomic sizes of alloys (i) and the total density of unoccupied d bands in platinum (ii) were considered. Via alloy formation, it was found that dilution of the active metal Pt occurred in these SiO 2 supported bimetallic catalysts, and the lattice parameter of Pt-M alloys decreased on Pt-Fe, Pt-Cu and Pt-Ga alloys, but increased on Pt-In and Pt-Sn alloys when compared with that of Pt foil. Catalytic activity was evidently shown to not be a function of the lattice parameters of Pt-M alloys, but appears closely related with the d -holes of Pt in Pt-M bimetallic catalysts. More d holes show favorably high activity. Among the studied Pt-M/SiO 2 (M= Fe, Cu, Ga, In and Sn) catalysts, the prominent and primary role of the electronic effect was demonstrated. • Mansour’method was used to quantitatively determine the electronic state of Pt. • Pt-Ga/SiO 2 catalyst exhibits biggest d -holes and highest initial conversion of propane. • The electronic effect plays a crucial role in studied systems.

Assembly‐In‐Foam Approach to Construct Nanodiamond/Carbon Nanotube Hybrid Monolithic Carbocatalysts for Direct Dehydrogenation of Ethylbenzene to Styrene

AbstractSustainable nanocarbon catalysts have made measurable progress in ethylbenzene direct dehydrogenation (DDH). Thanks for the distinctive physical and chemical properties of Nanodiamond (ND), the considerable attention have been paid to diverse catalytic transform processes involving the DDH reaction. However, the powder‐form carbon cannot be directly used in fixed‐bed reactors owing to the resulting huge pressure drop. Herein, inspired by the ship‐in‐boat strategy, we present an ingenious assembly‐in‐foam approach for the preparation of a novel hybrid structured monolithic catalyst featuring an aerogel of sulfur‐doped nanodiamonds/carbon nanotubes hybrid within the macropores of SiC foam (ND−CNT−SDS/SiC) by heating the freeze‐dried macroporous hybrid gels composed of CNT, ND, and SDS in N2 atmosphere. Owing to the promoted NDs dispersion, strengthened mass transfer, and sulfur‐doping, the nanodiamonds/carbon nanotube hybrid foam monolithic catalyst exhibits a terrific catalytic performance with high stability for energy‐saving styrene production from DDH of ethylbenzene reaction, as well as overcoming the shortcomings of application of powder‐formed nanocarbon in heterogeneous catalysis. Furthermore, the emerging Assembly‐in‐Foam way for preparing nanocarbons‐based foam monolithic catalyst towards diverse chemical processes has been paved.

Petroleum pitch-derived porous carbon as a metal-free catalyst for direct propane dehydrogenation to propylene

Propane dehydrogenation (PDH), as one of the most promising strategies for propylene synthesis, has attracted tremendous attention with the increase of shale gas exploitation. The exploration of green and sustainable catalytic materials to replace the high-price (Pt-Sn/Al2O3) and environmentally unfavorable (Cr2O3/Al2O3) catalysts will drive the rapid development of PDH technology. Porous carbon-based materials have been proposed as ideal PDH catalysts due to their abundant surface quinone/ketone CO groups for C-H bond activation and well-developed pore structures for mass transfer. However, the facile preparation of carbon-based catalysts with controllable surface properties and unique architectures remains a challenge. And the structure-function relationship of carbon-based catalysts in PDH is also under debate. Herein, we report a simple and efficient synthetic method to prepare the porous carbon-based PDH catalysts with cheap and readily available petroleum pitch as carbon source. The surface chemical properties and architectures of the porous carbon-based catalysts can be precisely tailored by varying the activation temperature during the synthesis process. Various characterizations including X-ray photoelectron spectra, temperature-programmed pyrolysis curves, thermogravimetric analysis and morphology observations clarify that the plentiful surface quinone/ketone CO groups and appropriate adsorption/desorption strengths of reactant/products derived from the great specific surface area are vital factors that guarantee the excellent C-H bond activation capability (propane conversion 45.6%) and alkenes selectivity (73.9%, propylene and ethylene) of the petroleum pitch-derived porous carbon catalyst. This work not only provides a promising alternative catalyst for the PDH process but also enriches the application fields of the carbon-based catalysts.

Fully-exposed Pt clusters stabilized on Sn-decorated nanodiamond/graphene hybrid support for efficient ethylbenzene direct dehydrogenation

Fully-exposed Pt clusters stabilized on Sn-decorated nanodiamond/graphene hybrid support for efficient ethylbenzene direct dehydrogenation

Highly efficient propane dehydrogenation promoted by reverse water–gas shift reaction on Pt-Zn alloy surfaces

CO2-assisted propane dehydrogenation has been developed in propylene production technology to deal with thermodynamic equilibrium limitations. However, the rational design of catalysts is a crucial challenge in achieving high catalytic performances. Herein, we report the successful fabrication of highly dispersed PtZn alloy on hierarchical zeolites for CO2-assisted propane dehydrogenation through the reverse water–gas shift reaction (RWGS). Compared with monometallic Pt, the synergistic effect of PtZn plays a crucial role in both direct propane dehydrogenation and RWGS, resulting in an outstanding catalytic performance with a high turnover frequency (TOF) of 1.82 × 104h−1. From the catalytic point of view, Pt-Zn alloy surfaces facilitate the equilibrium shift in propane conversion by consuming produced H2 through RWGS with weakening CO-metal surface interaction revealed by operando studies and DFT calculations. These findings illustrate the conceptual design of alloy catalysts and allow insights into the mechanistic details of CO2-assisted alkane dehydrogenation.

Oxygen vacancy promoted CO2 activation over acidic-treated LaCoO3 for dry reforming of propane

Utilizing propane and CO2 as coreactants to produce syngas (CO/H2) via dry reforming shows several advantages over direct propane dehydrogenation and traditional methane dry reforming. It is of great importance to establish high-efficiency catalytic systems that can break C–C bonds and activate CO2 simultaneously. Herein, acidic H2O2 was applied to etch LaCoO3. Surprisingly, highly dispersed Co3O4 at the edges of support along with high oxygen vacancies were obtained from acidic H2O2 treatment. Furthermore, the treated LaCoO3 catalyst facilitated the generated intermediates of formate to convert into the desired products. The results showed that acidic H2O2 treated LaCoO3 catalyst can reach 18% for propane conversion and 35% for CO2 conversion at 550 °C, showing high catalytic activity. Consequently, the present work provides some ideas for the synthesis of efficient LaCoO3 catalysts for dry reforming of propane.

Butadiene production in membrane reactors: A techno-economic analysis

The direct dehydrogenation of butane (BDH) is emerging as an attractive on-purpose technology for the direct production of 1,3-butadine. However, its product yield is hindered by the high rate of carbon deposition associated to the high temperature required for the highly endothermic reaction. In this work, we evaluated the use of H2-selective membrane reactor, to increase the yield of the dehydrogenation process at milder operating conditions. The novel proposed membrane reactor (MR)-assisted BDH technology is compared from a techno-economic point of view with the benchmark technology. The results of this analysis reveal that the MR technology enables to work at milder operating temperatures (−85 °C), reducing carbon formation (−98.5%) and reactor duty (−10%). Due to the higher reaction yields, the MR-assisted BDH technology can lower the required shale gas-based feedstock, maintaining same production capacity as in the benchmark; this will result in an overall plant efficiency of 50.92% in the MR-assisted plant, compared to 37.7% of the benchmark case. This work demonstrates that MR-assisted technology is a valuable alternative to the conventional BDH technology, reducing of almost 20% the final cost of production of 1,3-butadiene, due to the lower installation costs and the higher energy efficiency.

Assessing the Nature of Active Sites on Nanodiamonds as Metal-Free Catalysts for the EB-to-ST Direct Dehydrogenation Using a Catalytic Approach

Assessing the Nature of Active Sites on Nanodiamonds as Metal-Free Catalysts for the EB-to-ST Direct Dehydrogenation Using a Catalytic Approach

Low-Temperature Nonoxidative Dehydrogenation of Propane over Sn-promoted Mo-Y Zeolite: Catalytic performance and nature of the active sites

Owing to its higher value and ever-growing market, the production of light olefins is more attractive for many refineries. Among the existing routes, on-purpose dehydrogenation technologies seek special attention for the production of light olefins. Here we report a Mo-based bi-metallic catalyst exhibiting highly selective, active and stable for the direct dehydrogenation of propane to propylene. A comprehensive surface study of the MoSn/Y catalyst has been acquired to understand the interatomic interactions between metals. Extended X-ray absorption fine structure analysis suggested the Mo-O species is highly dispersed along with Sn-O. The structure-yield relationship illustrates that the Pt does not affect the catalytic performance when compared to Pt free system. We achieved a 40.94% propylene yield over MoSn/Y catalyst with the gradual coke deposition rate of 5.4x10-3 gcoke.gcat-1.h−1.

High-performance of CrOx/HZSM-5 catalyst on non-oxidative dehydrogenation of C2H6 to C2H4: Effect of supporting materials and associated mechanism

Ethane (C2H6) is an important inexpensive and widely available fuel resource. High-value use of C2H6 has become increasingly important. Catalytic dehydrogenation of C2H6 to ethylene (C2H4) has attracted much attention in recent years due to its high energy efficiency. The direct non-oxidative ethane dehydrogenation (EDH) to ethylene is a promising strategy to produce ethylene and hydrogen at the same time. In this research, Cr/HZSM-5 catalyst with superior stability was synthesized and exhibited an C2H6 converting activity of 1.47 μmol/(g·s) with the corresponding C2H6 conversion and C2H4 selectivity of 37.3% and 90%, respectively. The synergistic effects of Si and Al in supporting materials were investigated by comparing Cr/HZSM-5 with SBA-15, SiO2 and Al2O3 supported ones, which contains either Al or Si with different structures. Characterization results indicated that the intimate interactions between Cr and support significantly improved the catalytic performance. The presence of Al in the support promoted the formation of more active Cr6+ species by forming the aluminum‑chromium-chromate (Cr-O-Al) structures which were more efficient to active C-H bond and form (Cr, Al)-OH groups during the reaction. Meanwhile, the formation of internal silanol group with the dissociative adsorbed H* could stabilized the active Cr phase to achieve a stable dehydrogenation activity.

Promoted MoxCy‐based Catalysts for the CO2 Oxidative Dehydrogenation of Ethane

AbstractThe CO2 oxidative dehydrogenation reaction has the potential to play a role in the advancement of CO2‐utilizing catalytic reactions, co‐activating CO2 and short‐chained alkanes. Transition metal carbides are promising catalysts for this reaction, in particular MoxCy, however catalytic stability is a major challenge. In this study, the addition of a promoter (Fe, K, Ni or Pt) has shown to significantly influence the crystal structure of the carbide system as well as the acid‐base characteristics. K promotion decreased the number of acid sites, limiting ethane activation and the removal of the oxygen surface species formed in CO2 activation. The catalysts deactivate due to oxidation to MoOx. Fe decreased the initial activity, but it increased the stability of the oxygen surface species, which enhanced the stability of the catalyst and ethylene selectivity to outperform the unpromoted sample. Oxidation of the carbide and carbon deposition during the reaction could not be prevented. Ni promotion increases the number of basic sites, enhancing the CO2 activation, shown by the highest activity obtained during the reverse water‐gas‐shift experiments. At higher CO2 content in the feed the dry‐reforming reaction becomes the dominant reaction pathway. Pt suppressed the dry‐reforming reaction, but instead increased the direct dehydrogenation activity, accompanied by a high degree of carbon deposition. No oxidation to MoOx was observed at a stoichiometric CO2 to C2H6 feed ratio.

Plastering Sponge with Nanocarbon-Containing Slurry to Construct Mechanically Robust Macroporous Monolithic Catalysts for Direct Dehydrogenation of Ethylbenzene.

Nanocarbons have shown great potential as a sustainable alternative to metal catalysts, but their powder form limits their industrial applications. The preparation of nanocarbon-based monolithic catalysts is a practical approach for overcoming the resulting pressure drop associated with their powder form. In our previous work, a ploycation-mediated approach was used to successfully prepare nanocarbon-containing monoliths. Unfortunately, because there are no macropores in the monolith, it needs to be crashed into millimeter-sized particles before application. Therefore, developing a facile method for preparing mechanically robust nanocarbon-based macroporous monolithic catalysts is vital but still challenging. Herein, evoked by swallows building their nests, we report an approach for successfully preparing a mechanically robust nanodiamond-based macroporous monolith catalyst by plastering melamine sponge (MS) with a slurry composed of nanodiamonds (NDs) and poly(imidazolium-methylene) chloride (PImM) followed by an annealing process. The macroporous monolith catalyst (ND/NCMS-NCPImM) containing NDs well dispersed in N-doped carbon is mechanically robust with enriched macroscopic pores. It exhibits outstanding catalysis toward ethylbenzene to styrene through a direct dehydrogenation reaction with a high styrene rate in a steady state (5.50 mmol g-1 h-1) and high styrene selectivity (99.5%). ND/NCMS-NCPImM shows much higher activity than powder ND by 1.9 fold. In addition, this work solves the significant problem of large pressure drop encountered with conventional powdered nanocarbon catalysts in the flow reactor. This work not only creates an excellent nanodiamond-based macroporous monolithic ethylbenzene direct dehydrogenation catalyst but also presents a promising avenue for preparing other macroporous monolithic catalysts for diverse transformations.

CO2 oxidative dehydrogenation of n-butane to butadiene over CrOx supported on CeZr solid solution

1,3-Butadiene (BD) is a key raw material for the synthesis of rubber, but its efficient synthesis is a challenge. Direct dehydrogenation of n-butane in CO2 (CO2ODHB) represents an ideal way to produce BD and use the waste CO2 source. In the present work, several catalysts of CrOx supported on CeZr solid solutions were developed and applied in catalyzing the CO2ODHB to BD. Among these, a 10%CrOx/Ce0.5Zr0.5O2 could achieve the reaction with 25% of n-butane conversion and 70% of BD selectivity at 823 K. The prepared catalysts were characterized using the techniques of XRD, UV–vis-DR, XPS, Raman, N2 adsorption/desorption, FT-IR, TEM, H2-TPR, NH3-TPD, and CO2-TPD, etc. The results indicated that compared with other catalysts, the 10% CrOx/Ce0.5Zr0.5O2 catalyst possessed the highest Cr6+ species concentration and balanced acidic-basic sites, contributing to the outstanding performance in the reaction. These findings provide a strategy to build a catalyst with the stable valence of Cr6+ species, and hopefully, offer an important reference to establish other CeZr solid solution catalysts with regulable acidic-basic and textural properties.

Role of Cr on Cu-Cr catalyst via direct ethanol dehydrogenation to ethyl acetate

This study aims to convert ethanol to ethyl acetate and acetaldehyde using the catalytic ethanol dehydrogenation. The Cu-Cr catalysts were prepared via co-precipitation method using chromium (III) nitrate and copper nitrate precursors having different CuO weights between 50 and 80 wt% balancing with Cr2O3. The fresh catalyst was reduced by mixed gas of H2:N2 (10:90%) at 250ºC for 1 and 2 h (the non-reduced sample was also tested for comparative results). The structural properties of Cu-Cr catalysts were investigated by N2 physisorption, XRD, SEM-EDX, H2-TPR, XPS, NH3-TPD, and CO2-TPD. The ethanol dehydrogenation was carried out in a borosilicate glass fixed-bed continuous flow reactor at the specific condition [300 °C, atmospheric pressure, and WHSV = 3 (gethanol gcatalyst−1) h−1]. Based on the results, the ethyl acetate selectivity on 50 Cu-Cr catalyst (Low atomic Cu/Cr ratio) apparently increased by 1.6 times with increasing reduction time to 2 h having the highest ethyl acetate selectivity. Interestingly, the results from ethanol dehydrogenation indicated that the chromium promoter combining with CuxO in the 50 Cu-Cr catalyst increased the dispersion of copper species, facilitated the reduction, and increased the amount of Lewis acid sites. Moreover, the suitable reduction times can alter the distribution of CuCr2O4, Cu+, and Cu0, which resulted in increased ethyl acetate selectivity. The 50 Cu-Cr catalyst also exhibited good stability.

The triggering of catalysis via structural engineering at atomic level: Direct propane dehydrogenation on Fe-N3P-C

The on-purpose direct propane dehydrogenation (PDH) has received extensive attention to meet the ever-increasing demand of propylene. In this work, by means of density functional theory (DFT) calculations, we systematically studied the intrinsic coordinating effect of Fe single-atom catalysts in PDH. Interestingly, the N and P dual-coordinated single Fe (Fe-N3P-C) significantly outperform the Fe-N4C site in catalysis and exhibit desired activity and selectivity at industrial PDH temperatures. The mechanistic origin of different performance on Fe-N3P-C and Fe-N4C has been ascribed to the geometric effect. To be specific, the in-plane configuration of Fe-N4 site exhibits low H affinity, which results in poor activity in CH bond activations. By contrast, the out-of-plane structure of Fe-N3P-C site exhibits moderate H affinity, which not only promote the CH bond scission but also offer a platform for obtaining appropriate H diffusion rate which ensures the high selectivity of propylene and the regeneration of catalysts. This work demonstrates promising applications of dual-coordinated single-atom catalysts for highly selective propane dehydrogenation.

Fabrication of three dimensional SiC@C hybrid for efficient direct dehydrogenation of ethylbenzene to styrene

• The 3D carbon decorated SiC hybrid (core-shell structure) is first prepared by a simple template method as a potential robust metal free ethylbenzene DDH catalyst. • The SiC@C catalyst exhibits a large specific area (410.30 m 2 g −1 ) and high catalytic activity (11.58 mmol g −1 carbon h −1 ) in DDH of EB, nearly 4 times that of nanodiamond. • The extraordinary catalytic performance is attributed to the abundant surface carbonyl groups on the carbon layers. • The unique 3D core shell structure can inhibit the aggregation of SiC@C nanocrystals and is benefit for the heat and mass transfer during the dehydrogenation reaction. Synthesis of hybrid carbon materials with core-shell structure and robust catalytic performance is of great research interest, and remains a great challenge in catalytic dehydrogenation of hydrocarbons reaction. In this paper, few-layer sp 2 carbon decorated SiC nanocrystals with core-shell structure (SiC@C) were fabricated through a dual-confined magnesiothermic method by employing glucose and SiO 2 as precursors. The SiC@C nanocrystals were further crosslinked to be a three dimensional (3D) mesoporous hybrid by the in situ generated carbon as binders and exhibiting a 410.30 m 2 g −1 large surface area. The as-prepared SiC@C hybrid materials as metal-free catalysts were evaluated in the steam-free direct dehydrogenation of ethylbenzene to styrene. Benefiting from the abundant surface carbonyl groups on the graphite carbon layers, the optimized yield rate of styrene normalized by carbon mass was as high as 11.58 mmol g −1 carbon h −1 , nearly 4 times that of nanodiamonds. Considering the low cost and excellent catalytic activity, the hybrid 3D SiC@C material may be a promising candidate for direct dehydrogenation of hydrocarbons.

Sequential and/or Simultaneous Wet-Impregnation Impact on the Mesoporous Pt/Sn/Zn/γ-Al2O3 Catalysts for the Direct Ethane Dehydrogenation

This study is aimed at investigating the impact of catalyst preparation’s approach (either sequential and/or simultaneous wet impregnation) to a mesoporous series of Pt/A, Sn/A, PtSn/A, SnPt/A, (PtSn)/A, (PtSn)Zn/A, and (PtSnZn)/A catalysts for direct ethane dehydrogenation. The (PtSn)/A and (PtSnZn)/A had shown both higher initial specific activity (s-1) and reaction rate constantKd(h-1) (13063.86 (s-1) and 12489.69 (s-1) and 0.09 (h-1) and 0.06 (h-1)), respectively. The catalyst preparation approach had direct impact to the availability and dispersion of mesoporous particles of either active metal and/or promoter that influences either to hinder the C-C cleavage and/or to promote C-H bond cleavage in the dehydrogenation of ethane to ethene. The active metal component was present in the form of Pt, Pt+2, Al+3, Sn+4, and Zn+2 states. The enhanced catalytic activity is attributed to the Pt4Sn and PtZn formed phases in addition to highly dispersed mesoporous Pt particles. Based on the obtained results, the catalysts prepared by using simultaneous wet impregnation had shown higher catalytic activity and catalyst stability as to that of sequential wet impregnation.