ArticleDehydrogenation of methylcyclohexane over Pt supported on Mg–Al mixed oxides catalyst: The effect of promoter Ir
Graphical abstract
Hydrogen evolution rate reached up to 578.7 mmol·gPt−1·min−1 in the dehydrogenation of methylcyclohexane on Pt–Ir supported on Mg–Al mixed oxide catalyst and no carbon deposition on the catalyst surface was observed after dehydrogenation reaction.
Introduction
Due to the declining fossil fuel reserves and environmental pollution problems, the exploitation and utilization of renewable and sustainable alternative energy to substitute or supplement fossil fuels is extremely urgent [1]. Hydrogen energy, derived from renewable wind or solar power via electrolysis, is characterized by large quantity, pollution-free and high gravimetric energy storage density, which is considered as an efficient and clean energy for various industrial applications [2]. However, for utilizing hydrogen energy in large scale, reversible hydrogenation–dehydrogenation cycles are widely accepted as a promising method for transportation and delivery of hydrogen, where hydrogen can be easily stored and released on demand via a catalytic process. Consequently, liquid organic hydrides are usually selected as hydrogen carries because of their advantages on hydrogen storage density and convenient transportation under relatively mild conditions [[3], [4], [5], [6]].
From an environmental point of view, methylcyclohexane (MCH) is one of suitable candidates as an organic hydride because both MCH and toluene exist as liquid state in the temperature range of − 50–100 °C, which is widely employed to study the storage and release of hydrogen, but the technology bottleneck is to develop an efficient dehydrogenation catalyst with high activity and stability. Pt based catalysts can selectively activate CH bond and decrease its activation energy but not break CC bond, presenting a promising application potential in dehydrogenation reaction. For example, Kustov et al. [7] had concluded that Pt/C had excellent performance in dehydrogenation of cyclic naphthenes. Biniwale et al. [8] had studied the dehydrogenation of MCH over Pt supported on metal oxides and obtained a hydrogen evolution rate over 21.1 mmol·(g met)−1·min−1. To further enhance the dehydrogenation activity, several strategies have been proposed, and adding promoter was an easy way to reach a satisfactory hydrogen evolution rate [[9], [10], [11], [12], [13], [14], [15], [16]]. Until now, some components such as Ca, Sn, Mn and Mo have been tested as a promoter [10,[16], [17], [18]], and the results showed that both the dehydrogenation activity and carbon deposition resistance were improved [19].
In addition, the support also has a great effect on the activity and stability of Pt-based catalysts. Li et al. [20] had reported that carbon materials with distinct microstructures could adjust the Pt particle size from 1 to 9 nm and found that high dehydrogenation activity of Pt/CNFs depended on a large fraction of boundary Pt atoms. Because the confinement effect of ordered mesochannels restricted the growth of Pt nanoparticles, Pt-SBA-15 showed higher stability than Pt-SiO2 in the dehydrogenation reaction [21]. Recently, to lower the acidity of Al2O3 support and then enhance the resistance for coke formation, some alkaline or alkaline earth metals were added into Al2O3. Zhou et al. [22] had reported that the agglomeration of metallic particles was suppressed while both the dehydrogenation activity and stability were enhanced when mesoporous Al2O3 was modified by magnesium. Our previous investigation had also indicated that Mg–Al mixed oxides were good supports for Pt based catalysts in the dehydrogenation of MCH and the presence of Sn could enhance the activity, but the hydrogen evolution rate required to be further improved [14]. Hence, this study employed iridium (Ir) as a promoter for Pt supported on Mg–Al mixed oxides catalyst and concentrated on the effects of iridium content, catalyst reduction temperature, reaction temperature, flow rate and residence time on the hydrogen evolution rate in the dehydrogenation of MCH.
Section snippets
Experimental
Mg–Al hydrotalcite was prepared by a constant-pH co-precipitation method as reported in the previous literatures [23,24]. Pt–Ir supported on Mg–Al mixed oxides catalysts were prepared by an incipient wetness impregnation of Mg–Al hydrotalcite with chloroplatinic acid and chloroiridic acid mixed solution and then reduced by hydrogen. The content of Pt in the catalyst was fixed to 2.0 wt%. The resultant catalysts were denoted as PtIr-X/Mg–Al-T, where X and T represented the mass percentage of Ir
Characterization of Pt–Ir supported on Mg–Al mixed oxides catalysts
Fig. 1 shows the XRD patterns of Pt–Ir supported on Mg–Al mixed oxides catalysts. Three peaks appeared at 2θ = 35.1°, 43.0° and 62.8° in Fig. 1(a) and (b) were attributed to the crystalline structure of MgO-Al2O3 [25]. In comparison with the XRD pattern of Mg–Al hydrotalcite in previous literatures [26,27], it was obvious that the typical hydrotalcite structure was destroyed and transformed into mixed oxides after calcination at 500 °C. Due to the low loading amount and the high dispersion,
Conclusions
The addition of Ir enhanced the dispersion of Pt and decreased the average metal particle size and facilitated the electronegativity of Pt. The metal particle size was enlarged with the raising of reduction temperature. During the dehydrogenation of MCH, toluene selectivity reached up to 99.9%. After optimizing the Ir content and reduction temperature, MCH conversion and hydrogen evolution rate was up to 91.1% and 263.9 mmol·(g Pt)−1·min−1 on PtIr-5/Mg–Al-275 at 300 °C, respectively, which was
Acknowledgements
This research was supported by the National Natural Science Foundation of China (Nos. 21676225 and 21776236), Natural Science Foundation of Hunan Province (2018JJ2384) and Scientific Research Fund of Hunan Provincial Education Department (19A478), Collaborative Innovation Centre of New Chemical Technologies for Environmental Benignity and Efficient Resource Utilization, and Engineering Research Centre of Chemical Process Simulation and Optimization of Ministry of Education.
References (38)
- et al.
Efficient evolution of hydrogen from liquid cycloalkanes over Pt-containing catalysts supported on active carbons under “wet–dry multiphase conditions”
Appl. Catal. A Gen.
(2002) - et al.
Investigation of the performance and deactivation behavior of Raney-Ni catalyst in continuous dehydrogenation of cyclohexane under multiphase reaction conditions
Appl. Catal. A Gen.
(2013) - et al.
The catalytic performance of Ni2P/Al2O3 catalyst in comparison with Ni/Al2O3 catalyst in dehydrogenation of cyclohexane
Appl. Catal. A Gen.
(2014) - et al.
Dehydrogenation of polycyclic naphthenes on a Pt/C catalyst for hydrogen storage in liquid organic hydrogen carriers
Fuel Process. Technol.
(2018) - et al.
Efficient hydrogen supply through catalytic dehydrogenation of methylcyclohexane over Pt/metal oxide catalysts
Int. J. Hydrog. Energy
(2010) - et al.
Effects of Mn addition on dehydrogenation of methylcyclohexane over Pt/Al2O3 catalyst
Appl. Catal. A Gen.
(2017) - et al.
Simulation and design of catalytic membrane reactor for hydrogen production via methylcyclohexane dehydrogenation
Int. J. Hydrog. Energy
(2017) - et al.
Equilibrium shift of methylcyclohexane dehydrogenation in a thermally stable organosilica membrane reactor for high-purity hydrogen production
Int. J. Hydrog. Energy
(2013) - et al.
Dehydrogenation of methylcyclohexane over Pt/V2O5 and Pt/Y2O3 for hydrogen delivery applications
Int. J. Hydrog. Energy
(2012) - et al.
Dehydrogenation of methylcyclohexane over PtSn supported on MgAl mixed metal oxides derived from layered double hydroxides
Int. J. Hydrog. Energy
(2018)
Hydrogen production by catalytic dehydrogenation of methylcyclohexane over Pt catalysts supported on pyrolytic waste tire char
Int. J. Hydrog. Energy
Dehydrogenation of methylcyclohexane to toluene over partially reduced silica-supported Pt-Mo catalysts
J. Mol. Catal. A Chem.
Enhanced performance of Ca-doped Pt/γ-Al2O3 catalyst for cyclohexane dehydrogenation
Int. J. Hydrog. Energy
Microwave assisted synthesis of Sn-modified MgAlO as support for platinum catalyst in cyclohexane dehydrogenation to cyclohexene
Appl. Catal. A: Gen.
Insight into the support effect on the particle size effect of Pt/C catalysts in dehydrogenation
J. Catal.
High stability of Ce-promoted Ni/Mg–Al catalysts derived from hydrotalcites in dry reforming of methane
Fuel
Transesterification of tributyrin with methanol over MgAl mixed oxides derived from MgAl hydrotalcites synthesized in the presence of glucose
Fuel Process. Technol.
Ni/MgO–Al2O3 catalyst derived from modified [Ni,Mg,Al]-LDH with NaOH for CO2 reforming of methane
Int. J. Hydrog. Energy
Mixed methanol/ethanol on transesterification of waste cooking oil using Mg/Al hydrotalcite catalyst
Energy
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