Improved catalytic stability of Pt/TiO2 catalysts for methylcyclohexane dehydrogenation via selenium addition

To improve the catalytic activity of Pt catalysts for methylcyclohexane (MCH) dehydrogenation, which is utilized for hydrogen transportation, the effects of the addition of Se on the performance of Pt/TiO₂ catalysts were investigated. In Se/Pt/TiO₂ catalysts, even a small amount of Se addition (Se/Pt = 0.01) improved the catalyst stability. Se was highly dispersed on the Pt/TiO₂ surface, without volatilizing in a reducing atmosphere at temperatures below 450 °C, and did not form an alloy with Pt. The analysis of adsorption-desorption characteristics revealed that the addition of Se promoted the desorption of products, including the main product, toluene. Moreover, an electron donation effect from Se to Pt was observed by FT-IR measurement after the reduction. The desorption characteristic caused by the electron donation effect suppressed the deterioration of the catalyst and allowed stable catalytic activity toward the MCH dehydrogenation reaction.     

Boosting the dehydrogenation efficiency of dodecahydro-N-ethylcarbazole by assembling Pt nanoparticles on the single-layer Ti3C2Tx MXene

As the candidates for large-scale hydrogen storage, liquid organic hydrogen carriers (LOHCs) exhibit evident advantages in hydrogen storage density and convenience of storage and transportation. Among them, NECZ (N-ethylcarbazole)/12H-NECZ (dodecahydro-N-ethylcarbazole) is considered as a typical system with the lower hydrogenation/dehydrogenation temperature. However, the low dehydrogenation efficiency restrict its commercial applications. In this work, the single-layer Ti₃C₂T_x MXene was employed as the support to load the Pt nanoparticles for the 12H-NECZ dehydrogenation reaction. The effect of transition metals, loading amounts and morphologies of catalysts were analyzed. It was found that the 3 wt% Pt/S–Ti₃C₂T_x catalyst exhibited the best catalytic performance with 100% conversion, 91.55% selectivity of NECZ and 5.62 wt% hydrogen release amount at 453 K, 101.325 kPa for 7 h. The product distributions and kinetics analysis suggested that the elementary reaction from 4H-NECZ to NECZ was the rate-limiting step. The selectivity of NECZ is sensitive to the dehydrogenation temperature. Combined with the XRD, SEM, HRTEM, XPS, BET and FT-IR results, it could be indicated that the special two-dimension structure of S–Ti₃C₂T_x and electronic effect between Pt and S–Ti₃C₂T_x enhanced the dehydrogenation efficiency of 12H-NECZ. The measurements of cyclic dehydrogenation indicated that the Pt/S–Ti₃C₂T_x catalyst exhibited good stability after 42 h. This work brought a new strategy for the design of efficient catalysts using two-dimensional materials in the applications of the liquid organic storage hydrogen technology.     

Enhancing selectivity and reducing cost for dehydrogenation of dodecahydro-N-ethylcarbazole by supporting platinum on titanium dioxide

N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NECZ/12H-NECZ) was a promising system for hydrogen storage applications. 1.0 wt% Pt/TiO₂ was regarded as the optimal loading in Pt/TiO₂ catalyst applied in the 12H-NECZ dehydrogenation reaction. The hydrogen release amount, selectivity to NECZ and TOF of 12H-NECZ dehydrogenation are 5.75 wt %, 98% and 229.73 min⁻¹ at 453 K. Compared with the commercial 5.0 wt% Pd and Pt-based catalysts, it exhibited very high activity, selectivity and stability for 12H-NECZ dehydrogenation with low Pt loading. Combined with the XRD, XPS, HRTEM, TPR analysis, it was indicated that the enhanced catalytic performance was due to the SMSI (strong metal-supporting interaction) between Pt and TiO₂ support, which accelerated the rate-limiting step and enhanced the whole dehydrogenation reaction. This work may be beneficial for the commercial application of Pt/TiO₂ catalysts in the Liquid Organic Hydrogen Carrier (LOHC) system.     

Preparation of Pt supported on mesoporous Mg–Al oxide catalysts for efficient dehydrogenation of methylcyclohexane

Hydrogen energy, characterizing by high-energy density, non-pollution and renewability, is regarded as an ideal clean green energy, and the chemical hydrogen storage is an optimal strategy to realize its large-scale utilization. In this study, to enhance the hydrogen evolution rate in the dehydrogenation of methylcyclohexane (MCH), Pt supported on Mg–Al oxide catalysts were prepared and the effects of the co-precipitation reaction time during the preparation of Mg–Al hydrotalcite on their structural properties were studied in detail. The results showed that both the pore diameter and Pt dispersion were increased after prolonging the precipitation reaction time. During the dehydrogenation of MCH, these resultant catalysts presented high activity and good stability: hydrogen evolution rate reached up to 1892 mmol·g_Pt^?1 min^?1 at 623 K and the conversion was still held at 92% after 218 h. Of course, a slight decrease on the conversion during the dehydrogenation reaction was also observed, which was mainly attributed to the aggregation of Pt particles at high temperature.     

Catalytic dehydrogenation study of dodecahydro-N-ethylcarbazole by noble metal supported on reduced graphene oxide

Through systematical experiments, a comparative study was conducted concerning several graphene-supported noble metal catalysts for dehydrogenation of dodecahydro-N-ethylcarbazole (12H-NEC). It was found that the catalytic activity of the prepared graphene-supported noble metal catalysts was following the order of Pd > Pt > Rh > Ru > Au for the dehydrogenation process. Pd supported on reduced graphene oxide (rGO) prepared by one-pot in situ synthesis has much more excellent catalytic performance than other kinds of catalysts investigated for comparison, simultaneously the using amount of noble metals can obviously be decreased. To be specific, at 453 K, the final dehydrogenation product catalyzed by the novel catalyst of Pd/rGO is N-ethylcarbazole (NEC) and the process selectivity was increased from 44.77% (commercial Pd/Al₂O₃) to 97.65%, as well as the dehydrogenation ratio reached 99.14%. In addition, the novel catalyst is also superior to other reported catalysts in terms of dehydrogenation performance of 12H-NEC. Its dehydrogenation activity at 443 and 433 K of Pd/rGO was tested and the catalytic performance keeps stable at the two temperatures. Based on the experimental data, kinetic calculation was carried out and some fundamental parameters regarding reaction kinetics was obtained.     

Dehydrogenation of methylcyclohexane over Pt/V2O5 and Pt/Y2O3 for hydrogen delivery applications

Dehydrogenation of methylcyclohexane (MCH) for hydrogen transportation and delivery application was carried out over 3 wt% Pt/V₂O₅ and 3 wt% Pt/Y₂O₃ catalyst. The catalytic activity was tested using a spray-pulse mode of reactor. Effective dehydrogenation of MCH under spray-pulse mode of reactant injection was observed. In terms of hydrogen evolution rate at 60 min from start of reaction the activity of 958 mmol/g/min was obtained at temperature of 350 °C. Nearly 100% selectivity toward hydrogen was obtained. A relatively high conversion of 98% was observed with 3 wt% Pt/Y₂O₃ at 60 min using an advanced spray-pulse reactor system. The catalysts were characterized using x-ray diffraction pattern (XRD), CO-chemisorption metal analysis, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis.     

Application of microwave synthesized Ag-Rh nanoparticles in cyclohexane dehydrogenation for enhanced H2 delivery

The catalytic dehydrogenation of liquid organic hydrides (LOH) is a promising route to deliver H₂ for various mobile and stationary applications. However, an efficient and low-cost dehydrogenation catalyst, as an alternative to Pt, is a key for the success of LOH-based H₂ supply. In a quest for such catalysts, we synthesized stable Ag-Rh bimetallic nanoparticles (BNP) supported on activated carbon cloth (ACC) and Y₂O₃ using the microwave-assisted polyol technique. The performance of these catalysts during dehydrogenation of LOH viz., cyclohexane, was evaluated at 300 °C using an advanced spray-pulse reactor system. The Ag:Rh ratio was optimized to maximize the cyclohexane conversion and H₂ evolution. The effect of Ag:Rh ratio, catalyst support, and synthesis method was investigated, too. The most stable H₂ evolution performance was exhibited by microwave-synthesized 1:4 Ag-Rh/Y₂O₃ catalyst with the cyclohexane conversion, dehydrogenation rate and H₂ evolution rate of 35.8%, 17.2 mmol/g_Met/min and 400 mmol/g_Met/min, respectively. Finally, the performance of catalysts used in this study was compared with the Pt-based catalysts.     

Efficient hydrogen supply through catalytic dehydrogenation of methylcyclohexane over Pt/metal oxide catalysts

This paper describes the results of experiments on dehydrogenation of methylcyclohexane over Pt supported on metal oxides (Pt/MO) and Pt supported on perovskite (Pt/Per) catalysts. The reaction is being considered as a means for delivery of hydrogen to fueling stations in the form of more easily transportable methylcyclohexane. Among Pt/MO catalysts, the best activity as determined by the hydrogen evolution rate was observed over Pt/La₂O₃ catalyst at 21.1 mmol/g_met/min. Perovskite-supported catalysts exhibited relatively higher activity and selectivity, with Pt/La_0.7Y_0.3NiO₃ giving the best performance. This Pt/Per catalyst had an activity of ca 45 mmol/g_met/min with nearly 100% selectivity towards dehydrogenation. The catalysts were characterized using XRD, CO-chemisorption and SEM-EDXA techniques. The present study reports catalysts that minimize the use of Pt and explores tailoring the properties of the perovskite structure.     

Study of the use of a Pd–Pt-based catalyst for the catalytic combustion of storage tank VOCs

Catalytic combustion is a very cost-effective way to eliminate volatile organic compounds (VOCs). The components of the VOCs in storage tanks are complex, with alkanes, alkenes and aromatic hydrocarbons being the main components. The aromatic hydrocarbons are the most difficult organic compounds among the storage tank VOCs in terms of catalysing combustion, and they are easy to cause catalyst carbon deposition. In this work, the Pt/γ-Al₂O₃, Pd/γ-Al₂O₃, Pd–Pt/γ-Al₂O₃, Pd–Pt/CeO₂/γ-Al₂O₃ and Pd–Pt/CeO₂/γ-Al₂O₃–N catalysts were prepared using an incipient wetness impregnation method. The performances of the catalysts were investigated using toluene and a simulation of VOCs in gas in a storage tank as model reactants. The study found that Pt has a higher catalytic combustion activity than Pd for the alkanes in the VOC gas in the simulation storage tank, and Pd has a higher catalytic combustion activity than Pt for the alkenes and toluene in the VOC gas in the simulation storage tank. The Pt addition enhances the activity of Pd-based catalysts for VOC catalytic combustion, and the Pd–Pt active component has good active stability. The catalyst prepared by using Pd–Pt alone has a defect in that it exhibits an insufficient oxygen supply performance in the catalytic combustion process. The addition of CeO₂ improves the oxygen supply performance of the Pd–Pt-based catalyst. In addition, the activity of the Pd–Pt/CeO₂/γ-Al₂O₃–N catalyst prepared by reducing the validated amount of Pd–Pt is higher than that of a commercial catalyst.     

Low-temperature selective dehydrogenation of methylcyclohexane by surface protonics over Pt/anatase-TiO2 catalyst

For a liquid organic hydride system used for a hydrogen carrier, methylcyclohexane (MCH)–toluene cycle is promising. In this cycle, dehydrogenation of MCH is an endothermic reaction and a key step. We have conducted dehydrogenation of MCH over Pt/anatase-TiO₂ catalyst in an electric field to promote MCH dehydrogenation at a temperature as low as 448 K. The electric field application brought high activity of 37% conversion even at 448 K, exceeding the thermodynamic equilibrium of 12%. This Pt/anatase-TiO₂ catalyst showed only a small amount of methane and carbon by-production and showed high activity for 360 min because of surface protonics.     

A comparative study of catalytic dehydrogenation of perhydro-N-ethylcarbazole over noble metal catalysts

N-ethylcarbazole is one of the most promising liquid organic hydrogen carriers (LOHCs) as it can be catalytically hydrogenated and dehydrogenated at relatively moderate temperatures. In the present work, we report a systematic study on dehydrogenation of perhydro-N-ethylcarbazole over several important supported noble metal catalysts to identify the optimal catalyst for temperature-controlled dehydrogenation. The reaction takes three consecutive stages with two intermediates of octahydro-N-ethylcarbazole and tetrahydro-N-ethylcarbazole. The initial catalytic activity of the selected noble metal catalysts for the dehydrogenation process was found to follow the order of Pd > Pt > Ru > Rh. 100% selectivity toward the final product of N-ethylcarbazole and fully dehydrogenation was achieved over the supported Pt and Pd catalysts. The kinetics of the three stage dehydrogenation processes over the catalysts was studied and the rate constants were derived. The results indicate that the dehydrogenation reaction rate decreases significantly with the reaction stage for all the selected noble catalysts and the conversion from tetrahydro-N-ethylcarbazole to N-ethylcarbazole was found to be the rate-limiting step of the entire reaction process.     

Synthesis of nano-tube CoNi/N–C complex and its catalytic properties for highly efficient oxygen reduction

Electrochemical energy storage systems such as fuel cells and metal air cells can be used as clean energy. In these systems, an essential reaction on the cathode is the oxygen reduction reaction (ORR). As ORR catalyst, non noble metal based catalyst is an important substitute for commercial Pt/C catalyst due to its rich reserves, low cost, good stability and high catalytic activity. Herein, CoNi alloy supported on nitrogen doped carbon, CoNi/N–C nanotubes, prepared by hydrothermal method and high-temperature pyrolysis method, shows excellent ORR catalytic activity and stability in 0.1 M KOH solution. In particular, the obtained CoNi/N-C-800 demonstrates the highest ORR activity of the prepared samples, with a half wave potential of 0.81V, which was equivalent to the commercially available Pt/C (0.82V). At the same time, it exhibits approximate 4e^- pathway with a comparable electron transfer number to the commercial Pt/C, and is much higher tolerant in methanol than the latter. Co and Ni alloying can induce the internal electron interaction of the catalyst, thus exposing more active sites. Furthermore, nano-tube CoNi exhibits appropriate size and hollow geometry, and its large surface area and strong conductivity improve its catalytic activity. The results may possibly provide a new impetus to the rational design of non noble metal based nanocomposite catalysts. Moreover, it is also of great significance to improve the performance of electrocatalysis and energy storage applications.     

Effects of the composition on the active carbon supported Pd–Pt bimetallic catalysts for HI decomposition in the iodine–sulfur cycle

A series of binary Pd–Pt catalysts supported on active carbon were prepared by the co-impregnation and reduction method. For comparison, active carbon supported monometallic Pt and Pd catalysts were also prepared by the impregnation–reduction method. Their structure, morphology and surface area were investigated by means of X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) surface area, respectively. Their catalytic activities were evaluated for the decomposition of hydrogen iodide (HI). Furthermore, their thermal stabilities were also investigated. The results of activity tests showed that the composition of Pd–Pt binary catalysts played the important role in dictating the catalyst activity. Among the Pt, Pd and binary Pd–Pt catalysts, the 2.5%Pd–2.5%Pt/C showed the best catalytic performance for the decomposition of HI. The results of thermal stability tests showed that the binary Pd–Pt catalyst had the higher stability than the monometallic Pt and Pd catalysts.     

Synergistic effect of metal components of the low-loaded Pt-Ni-Cr/C catalyst in the bicyclohexyl dehydrogenation reaction

The problem of hydrogen storage in liquid organic hydrogen carriers is not only the choice of an appropriate organic substrate, but the development of a selective and active catalyst containing as low as possible noble metals. A synergistic effect of increasing conversion and selectivity in bicyclohexyl dehydrogenation to biphenyl on trimetallic Pt-Ni-Cr/C catalysts with an extremely low Pt loading (0.1 wt %), compared with bimetallic Ni-Cr/C and Pt/Ni/C systems, due to the supporting of platinum on nickel-chromium nanoparticles was established for the first time. The TOF values (mmol (H₂)/g_Pt min) for hydrogen evolution under conditions of the reaction of bicyclohexyl dehydrogenation (320 °C, 0.1 MPa) on Pt supported onto a Ni-Cr/С composite exceed by two orders of magnitude the values found for the two-component catalysts. The maximum amount of the evolved hydrogen correlates to the selectivity of the complete dehydrogenation of bicyclohexyl into biphenyl on the Pt-Ni-Cr/C catalyst. The formation of a Ni-Cr solid substitution solution in a Ni-Cr composite deposited on a carbon carrier is shown by magnetometry, XRD, and TEM methods.     

Activity and stability of Pt catalysts supported on carbon nanotubes,active carbon and γ-Al2O3 for HI decomposition in iodine–sulfur thermochemical cycle

Pt catalysts supported on carbon nanotubes (CNT), activated carbon and γ-Al₂O₃ were prepared by the electroless plating method. For comparison, the CNT supported Pt was also prepared by the traditional impregnation–reduction method. The physical properties, structure, morphology and Pt loadings of the different catalysts were characterized by BET, XRD, TEM and ICP, respectively. The catalytic activity for HI decomposition was investigated in a fixed bed reactor under atmospheric pressure. The results of XRD and the activity evaluation indicated that the Pt/CNT prepared by the electroless plating method had better catalytic performance than that prepared by the impregnation–reduction method. Among the three kinds of supported Pt catalysts by the electroless plating method, the CNT supported Pt catalyst not only showed the highest activity for HI decomposition, but also had the best stability in specific surface area, structure and morphology.     

A new hydrogen storage system based on efficient reversible catalytic hydrogenation/dehydrogenation of terphenyl

Noble metal catalysts on mesoporous SiO₂ and modified carbon supports were found to enhance the activities of terphenyl (TPh) hydrogenation and tercyclohexane (TCH) dehydrogenation without side reactions, such as cracking, hydrogenolysis, ring opening and/or coke formation. The noble metal catalysts could be used for a reversible hydrogen storage system. Five percent Pt/SiO₂ catalyst was highly active in TCH dehydrogenation without stirring, due to an easier diffusion of organic molecules to the small catalyst particles during dehydrogenation.     

Bamboo fungus-derived magnetic porous carbon encapsulated nickel stabilized Rh nanoparticles as efficient catalysts for hydrolytic dehydrogenation of ammonia borane

Biomass-derived porous carbons are generally used as supports for metal nanoparticle (NP) stabilizations, while the strong hydrophilicity of such materials makes the as-prepared catalysts hard to be isolated after reaction, significantly affecting their potential applications. Herein, magnetic N-functionalized carbon (CN) encapsulated Ni composite (Ni@CN) prepared via pyrolysis of bamboo fungus pre-absorbed with nickel nitrate is exploited as a matrix to synthesize Rh/Ni@CN hybrid, which can be used as a magnetically recoverable catalytic material for hydrolytic dehydrogenation of ammonia borane (AB) to generate hydrogen. The Rh/Ni@CN (Rh loading: 0.84 wt%) exhibits an optimal activity (turnover frequency: 351 min⁻¹) for hydrogen evolution from hydrolytic dehydrogenation of AB. Most importantly, this catalyst can be simply isolated by a magnet and reused at least five times with complete conversion of AB to hydrogen. The strong interaction between the two metals and the small size of Rh NPs are responsible for the improved catalytic activity for hydrolytic dehydrogenation of AB. This work provides an eco-friendly and efficient strategy to fabricate excellent catalysts in catalytic applications.     

Nano-Pd/CeO2 catalysts for hydrogen storage by reversible benzene hydrogenation/dehydrogenation reactions

Nano-CeO₂ supports, which have different structure from different preparation methods, were used to prepare nano-Pd/CeO₂ catalysts. The hydrogen storage capacity of prepared nano-Pd/CeO₂ catalysts were studied via vapor phase benzene hydrogenation and cyclohexane dehydrogenation reactions. Results show that the prepared Pd/CeO₂ catalysts exhibit excellent benzene hydrogenation and cyclohexane dehydrogenation performances. The catalytic performance of the Pd/CeO₂ catalysts is related to the dispersion of metallic Pd, hydrogen adsorption-desorption ability and structure of Pd/CeO₂ catalysts and so on. And those properties are also directly affected by the morphology and mesoporous structure of the prepared nano-Pd/CeO₂ catalysts that can be regulated by CeO₂ support preparation methods. The synergistic effect between metal Pd, CeO₂ support and their structures can effectively promote benzene hydrogenation and cyclohexane dehydrogenation, thus promoting hydrogen storage capacity. The prepared Pd/CeO₂-HT catalyst, which has high specific surface area, developed pore structure and highly dispersed metal Pd species, exhibits superior catalytic performances. And, the Pd/CeO₂-HT catalyst exhibits superior catalytic hydrogen storage performances. The benzene conversion over it at 200 °C reaches 99.5%. Whereas the cyclohexane conversion at 450 °C is 65.3%, and the H₂ production capacity is 73.77 g/h.     

A experimental study on the dehydrogenation performance of dodecahydro-N-ethylcarbazole on M/TiO2 catalysts

Liquid organic hydrogen carrier (LOHC) is considered as a promising candidate for large-scale hydrogen storage. In this work, we found that Pt/TiO₂ catalysts exhibited better catalytic activity and selectivity compared to Pd/TiO₂ and commercial Pd/Al₂O₃ catalysts in the dehydrogenation of dodecahydro-N-ethylcarbazole (12H-NECZ) at 453 K. The catalytic activity of the noble metal catalysts followed the trend of Pt/TiO₂ > Pd/TiO₂ > Rh/TiO₂ > Au/TiO₂ > Ru/TiO₂. Compared with the commercial Pd/Al₂O₃, Pt/TiO₂ greatly improved the selectivity and conversion rate, the reaction time was also shortened. In addition, kinetics calculation was carried out to obtain fundamental reaction parameters. It was found that the third step of 4H-NECZ dehydrogenation to NECZ was the rate-limiting step of the entire dehydrogenation reaction for all catalysts.     

Hydrogen production by catalytic dehydrogenation of methylcyclohexane over Pt catalysts supported on pyrolytic waste tire char

Pyrolytic waste tire char was modified to be used as support and a series of catalysts supported with 0.1-1.0 wt% Pt were prepared by conventional wetness impregnation method. TEM images show that the Pt nanoparticles are well-dispersed in any microregions in the sample view on the TEM grid. The results of methylcyclohexane dehydrogenation reaction show the Pt loadings and the reaction temperature have a significant impact on the catalytic activity.