Activity For Cyclohexane Dehydrogenation Research Articles

Stable Pt/MgAl2O4 catalysts for efficient production of H2 from cyclohexane dehydrogenation

Cyclohexane as liquid organic hydrogen carriers has attracted considerable interest in the field of hydrogen storage technology. However, the innovation of efficient catalyst for producing H2 through cyclohexane dehydrogenation remains a substantial challenge. In this study, we have successfully developed Pt/MgAl2O4 catalysts exhibiting outstanding catalytic performance in cyclohexane dehydrogenation. Notably, the optimal catalyst Pt/MgAl2O4-700 achieves cyclohexane conversion of 89.1 % and benzene selectivity of over 99 % at 345 °C, resulting in a high hydrogen evolution rate of 933 mmol/gPt/min. Moreover, this catalyst exhibits remarkable long-term stability, with no evident loss of activity in 225-hour dehydrogenation reaction. The catalyst was characterized by XRD, N2 adsorption–desorption, STEM, XPS, NH3-TPD, CO-FTIR and H2-TPR techniques, which provides detailed structure information for elucidation of structure–activity relationship. The spinel structure and moderate acid density of the support enable highly dispersed Pt species at the surface of MgAl2O4. This results in the formation of ultra-small and sintering-resistant Pt particles that exhibit exceptional activity in cyclohexane dehydrogenation. Additionally, the presence of positively charged Ptδ+ species in Pt/MgAl2O4 facilitates the rapid desorption of benzene product. This effectively prevents the formation of coke arising from benzene dehydrogenation, which ensures to achieve high stability. These findings provide valuable knowledge for the rational design of efficient metal-based catalysts for liquid organic hydrogen carriers in hydrogen storage systems.

Nitrogen-doped carbon supported PtPd alloy nanoparticles exhibiting high catalytic activity for cyclohexane dehydrogenation under low temperatures

While Pt-based heterogeneous catalysts have been extensively studied for cyclohexane dehydrogenation, the reaction efficiency under low temperatures remains to be resolved. In this paper, ultrafine PtPd alloy nanoparticles homogeneously anchored on nitrogen-doped carbon were synthesized and applied for cyclohexane dehydrogenation. The experimental results indicate that the synergistic effect of Pt-Pd in PtPd/CN catalyst enhances the activity and durability of the catalyst in cyclohexane dehydrogenation compared with Pt/CN and Pd/CN catalysts. The as-prepared catalyst (labeled as Pt0.75Pd0.25/CN) exhibits an excellent catalytic performance with an initial TOF value of 90.07 mmol·g−1metal·min−1 and a 100% H2 purity for cyclohexane dehydrogenation at 180 °C, exceeding reported values under comparable reaction conditions. Catalyst characterizations and DFT calculations reveal that the electronic coupling effect of Pd and Pt in PtPd/CN catalyst makes the d-band center of Pt active sites closer to the Fermi level, which promotes the specific adsorption/activation of cyclohexane on Pt active sites, thus improving the catalytic performance of cyclohexane dehydrogenation. Under this guidance, the synthesized PtRu/CN and PtIr/CN alloy catalysts exhibited similar enhanced activity in cyclohexane dehydrogenation. This work provides insights into the rational design of efficient and stable Pt-based bimetallic catalysts for cyclohexane dehydrogenation.

Hollow Hemispherical Carbon Microspheres with Mo2C Nanoparticles Synthesized by Precursor Design: Effective Noble Metal‐Free Catalysts for Dehydrogenation

AbstractNoble metal‐based catalysts are currently widely used for the dehydrogenation of hydrocarbons or the production of H2 from hydrocarbons for various applications. However, these catalysts are expensive and hard to scale up. In this work, a facile template‐assisted synthesis of hollow carbon microspheres possessing ultrasmall molybdenum carbide (Mo2C) nanoparticles (NPs) that can efficiently catalyze the dehydrogenation of hydrocarbons is reported. The hollow structures and catalytic activity of the materials can be tuned, or optimized, by controlling the relative amount of Mo species or template used in their precursors. The bowl‐like hemispherical carbons with ≈20 nm thin shells and <5 nm in diameter Mo2C NPs show superior catalytic activity for dehydrogenation of cyclohexane, with a turnover frequency value of 1 × 10−4 s−1 at 305 °C. The catalytic activity of these microspheres for the reaction is 15 times higher than that of the corresponding incomplete hollow spherical carbon microparticles possessing similar sized Mo2C NPs and also better than that of activated carbon‐supported Pt (Pt/AC). Interestingly also, adding a mere 0.1% Pt into the materials leads to several‐fold increase in their catalytic activity and much higher activity than that of Pt/AC.

On the role of size controlled Pt particles in nanostructured Pt-containing Al2O3 catalysts for partial oxidation of methane

The effect of the Pt loadings and particles sizes on the stability of Pt(x wt%)/Al2O3 catalysts were investigated in the partial oxidation of methane (POM) reaction. The Al2O3 support was prepared by sol-gel method and different Pt loadings, varying from 0.5 to 2.0 wt% were incorporated to alumina through the incipient wetness impregnation method. The physicochemical features of the catalysts were determined by XRD, ICP-OES, Nitrogen-sorption, UV–Visible, H2-TPR, CO-DRIFTS, SEM-EDS, XPS and HRTEM techniques. The metal dispersion was evaluated in the cyclohexane dehydrogenation reaction. Lower Pt loadings resulted in well dispersed Pto nanoparticles with an enhanced activity in cyclohexane dehydrogenation and POM reactions. With increasing Pt loading to 2.0 wt%, the Pt nanoparticles of the Pt(2.0 wt%)/Al2O3 showed a methane conversion of 63% in 24 h of time on stream, and the catalyst was very selective to H2 and CO. Based on the HRTEM, XPS and Raman spectroscopy techniques, an increment in the Pt loadings evidenced an enrichment of Pto clusters on the surface, however, no heavy carbon deposits formation was observed.

Reforming of cyclohexane and n-heptane on nanosized Mo2C and W2C obtained by the carbidization of WO3 and MoO3 activated by vibrationally excited molecules of hydrogen

The catalytic activity of nanosized powders of hexagonal α-Mo2C and α-W2C with average particle size of 17 nm obtained by thermal carbidization of MoO3 and WO3 oxides in the flow of methane–hydrogen mixture, preliminarily activated by the vibrationally excited molecules of hydrogen was studied. Amorphous powders obtained by this method exhibit high activity associated with structural features. This was a crucial factor for the low-temperature synthesis of nanosized carbides (500 °C for Mo2C and 600 °C for W2C). It was shown that nanosized carbides exhibit high catalytic activity in cyclohexane dehydrogenation yielding benzene, and cyclodehydrogenation of n-heptane yielding toluene. The analysis of the obtained data allow to conclude that the observed drastic difference in activity and selectivity of the carbides with nano- and microsized particles is conditioned by the effect of nanocarbides particle size and defects of structure that have been formed during low-temperature synthesis. The synthesized carbide catalysts are stable in air and keep their catalytic activity over a long period.

Investigation of the performance and deactivation behavior of Raney-Ni catalyst in continuous dehydrogenation of cyclohexane under multiphase reaction conditions

The performance and deactivation behavior of Raney-Ni catalyst in continuous dehydrogenation of cyclohexane under multiphase reaction conditions were investigated in this paper. The experimental results showed that Raney-Ni had excellent catalytic activity for dehydrogenation of cyclohexane. Without assistance of any sweeping or carrier gas, the highest hydrogen evolution rate per unit reaction area could reach 0.20mmolcm−2min−1 at 322°C with a cyclohexane feeding rate of 8.5mmolmin−1 and Raney-Ni catalyst dosage of 3g. However, the deactivation of Raney-Ni catalyst was also observed during the course of reaction. The deactivation kinetics of Raney-Ni was studied, and the orders of deactivation at different reaction temperatures were determined, which showed that the decay of Raney-Ni catalyst was parallel deactivation. The equations of hydrogen evolution rates at different reaction temperatures were deduced from the deactivation kinetic equations. Due to the strong purging effect caused by the rapid evaporation of liquid organics on the catalyst surface under multiphase reaction conditions, the dehydrogenation reaction was confined to the outer layers of catalyst pallet and an ultralow apparent activation energy of 20.60kJmol−1 was obtained.

Crystal phase dependent metal–support interactions in Pt/SO 42−-ZrO 2 catalysts for hydroconversion of n-alkanes

In order to elucidate the influence of the crystal structure of zirconia on the properties of the metallic and acid function of Pt/SO 4 2−-ZrO 2, catalysts with different zirconia crystal phases were synthesized, fully tetragonal, fully monoclinic, and with a mixture of the tetragonal and monoclinic phases. Their catalytic properties were studied in the metal-catalyzed reaction of cyclohexane dehydrogenation (300 °C, 0.1 MPa, WHSV=10 h −1 , H 2/C 6H 12=30), the acid-catalyzed isomerization of n-butane (350 °C, 0.1 MPa, WHSV=1 h −1 , H 2/C 4H 10=6), and the bifunctional hydroconversion of n-octane (300 °C, 1.5 MPa, WHSV=4 h −1 , H 2/C 8H 18=6). TPR, XRD and FTIR of chemisorbed CO were also used in order to characterize the catalysts. The results showed a strong influence of the crystal phase on the activity of the acid function. A less marked effect was found for the metal-catalyzed reaction. An opposite relation between the two functions was seen with respect to this crystal structure influence. Among the sulfated catalysts, monoclinic Pt/SO 4 2−-ZrO 2 had the lowest activity in n-C 4 isomerization and the highest activity in cyclohexane dehydrogenation. Tetragonal Pt/SO 4 2−-ZrO 2 catalysts were the most active in isomerization of n-butane. They had the lowest activity in cyclohexane dehydrogenation and their metal properties were negligible. They were also the most active in n-C 8 conversion, producing mainly i-C 4. Monoclinic catalysts had low cracking activity and produced mainly isooctane. Mixed phase catalysts had an intermediate behavior. While S poisoning of Pt was present as a uniform effect on all sulfated catalysts, the metal–acid behavior and the different Pt properties could be explained by a metal–support interaction between tetragonal SO 4 2−-ZrO 2 and Pt. The Pt–support interaction was analyzed both with a model of Pt particles encapsulation and a model of electron depletion. The electronic deficiency of Pt particles supported on SO 4 2−-ZrO 2 was evident in the shift of the IR bands of adsorbed CO. Further experimental work is however needed to get conclusive evidence about the nature of the Pt–support interaction.

Catalytic Activity of Ni/(P)Ti-HMS Catalysts with Varying Phosphorous Concentration in The reaction Of dehydrogenation of Cyclohexane

AbstractNi/(P)Ti-HMS catalysts were prepared and characterized by several physicochernical techniques. The addition of phosphorous to the original mesoporous materials modified the acid-base surface properties. The activity in cyclohexane dehydrogenation is higher than on conventional catalysts.

Amorphous PdSi alloys for hydrogen-permeable and catalytically active membranes

Amorphous Pd x Si 1- x ( x=0.8,0.825,0.85) in the form of ribbon was prepared by a single-roller melt spinning technique to examine hydrogen permeability and catalytic activity for dehydrogenation. As a result, it was found that the amorphous specimens had higher tenacity and higher permeability of hydrogen than its crystallized form. Also, the surface of the amorphous specimen showed a catalytic activity for dehydrogenation of cyclohexane, while no activity was observed in the untreated. Taking advantage of both hydrogen permeability and catalytic activity, the amorphous Pd xSi 1-x would be expected to be a candidate for a catalytic membrane.

Propene aromatization over alkali-exchanged ZSM-5 zeolites

The transformation of propene was carried out over alkali-exchanged ZSM-5 zeolites. Compared with H-ZSM-5, the alkali-exchanged ZSM-5 showed lower activity but higher selectivity to benzene among aromatics. Furthermore, they displayed activity for dehydrogenation of cyclohexane to form benzene. Infrared results using both pyridine and pyrrole as probe molecules revealed that these alkali-ZSM-5 samples do not contain Brønsted acid sites, however strong Lewis acid sites and also weak Lewis basic sites are present. The oligomerization of propene and the further dehydrocyclization are suggested to comprise the reaction route for benzene formation, the active sites for these reactions are Lewis acid sites, which should be regarded as acid-base pairs of alkali—cation and the neighbouring basic oxygen. A mechanism involving these Lewis acid—base pairs is proposed for the observed products of methylpentene.

Studies of molybdena-alumina catalysts

MoO 3Al 2O 3 catalysts over the loading range 3.9 to 14.9 wt% MoO 3 have been studied. Although the BET surface areas in the higher valent (MoO 3) form are compatible with a monolayer model, the areas after H 2 reduction at 500 °C are not; the appropriate model would be porous or finely crystalline MoO 2 produced by reduction. For reduced catalysts, the curve for O 2 chemisorption (at −78 °C) vs molybdena loading is concave upwards. The origin of this behavior seems to be incomplete reduction (of MoO 3 to MoO 2, after 6 hr at 500 °C in flowing H 2) for catalysts containing less than about 11 wt% MoO 3. If correction is made for the actual extent of reduction at 500 °C, then O 2 chemisorption vs loading is essentially a straight line through the origin. Activity for cyclohexane dehydrogenation at 500 °C vs molybdena loading is also a curve concave upward; again, correction for the actual amount of MoO 3 reduced during prereduction changes the curve to one that is slightly convex upward. The sites responsible for both O 2 chemisorption and cyclohexane dehydrogenation may correspond to surface Mo 4+ ions, but this is not proven.

Catalytic properties of zeolites canix in cyclohexane dehydrogenation

The authors show the feasibility of synthesis of polycation forms of zeolites with a low active component content, superior in catalytic activity in cyclohexane dehydrogenation to zeolites containing only an active component.

Supported “bimetallic cluster” catalysts

Silica-supported ruthenium-copper and osmium-copper catalysts have been investigated for the hydrogenolysis of ethane to methane and for the dehydrogenation of cyclohexane to benzene. Cyclohexane also exhibits a hydrogenolysis reaction on these catalysts, yielding methane as the predominant primary product. The ruthenium or osmium concentration in the catalysts was held constant at 1 wt%, while the atomic ratio of copper to ruthenium, or copper to osmium, was varied from 0 to 1. Despite the low metal concentration and attendant high metal dispersion, and the fact that copper is virtually totally immiscible with ruthenium or osmium in the bulk, the incorporation of the copper inhibited markedly the specific activity of ruthenium or osmium for hydrogenolysis. The specific activity for dehydrogenation of cyclohexane to benzene was affected very little. It is proposed that highly dispersed “bimetallic clusters” of ruthenium-copper and osmium-copper exist on the carrier.

Studies on a Dispersion State of Ferric Oxide Deposited on Porous Vycor Glass and Its Catalytic Activity for Dehydrogenation of Cyclohexane

毛管構造のわかつている多孔性バイコールガラスに沈積した酸化鉄について,分散状態と触媒活性との関係を検討した。酸化鉄沈積量f-0.064～0.206(g/g-carr)の試料について,0℃におけるn-キサンの執着.脱着等温線を測定した.酸化鉄が担体を構成している単位粒子の表面に均一に分散しているとすると, fの増加こともなう等温線の変化がよく説明できる.一方パルス法により,f-0～0.206の触媒についてシクロヘキサンのベンゼンへの脱水素反応活性を測定した。触媒活性は最初はfに比例して増加するが,fがさらに大きくなると一定値に収敏する。活性が一定になるところでの沈酸化鉄層の厚さはα型酸化鉄の格子定数,5.4Åに近い。沈積酸化鉄量がきわめて少なければ完全な活性を示さないであろうが,少なくとも格子定数以上の厚さになれば十分な活性を示すと考えると,f の増加にともなう活性の変化を, 収着法の場合と同一の分散モデルで無理なく説明できることを述べた。