Microstructured CeO2-NiO-Al2O3/Ni-foam catalyst for oxidative dehydrogenation of ethane to ethylene

doi:10.1016/j.catcom.2016.10.004

Catalysis Communications

Volume 88, 5 January 2017, Pages 90-93

https://doi.org/10.1016/j.catcom.2016.10.004 Get rights and content

Highlights

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CeO₂-NiO-Al₂O₃/Ni-foam is obtained by chemically etching Ni-foam and modifying with CeO₂.
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CeO₂-NiO-Al₂O₃ nanocomposite catalyst is uniformly embedded onto the Ni-foam struts.
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Such catalyst is highly active and selective with promising stability for the ODE process.
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Foam-structuring endows catalyst with high heat/mass transfer and high permeability.
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Fascinating C₂H₄ productivity is obtainable over the 7CeO₂-NiO-Al₂O₃/Ni-foam catalyst.

Abstract

Ni-foam-structured CeO₂-NiO-Al₂O₃ catalysts to be used for oxidative dehydrogenation of ethane to ethylene (ODE) have been developed, via chemically etching a Ni-foam followed by CeO₂ modification. The CeO₂-NiO-Al₂O₃/Ni-foam catalysts are highly active and selective with promising stability. With the increase in CeO₂ loading up to 10 wt%, ethane conversion is increased monotonously while ethylene selectivity shows volcano-shaped evolution and reaches its maxima at 7 wt% CeO₂ loading. A high ethylene productivity of 425 g_Ethylene kg_cat^− 1 h^− 1 is achieved for a feed gas of C₂H₆/O₂/N₂ = 1/1/8 at 450 °C and a gas hourly space velocity of 18,000 cm³ g^− 1 h^− 1. Promotion effect of CeO₂ additive is also discussed.

Graphical abstract

Introduction

Ethylene is one of the most important commodity chemicals, going toward various high value-added products such as polyethylene, ethylene oxide, ethylene dichloride and ethylbenzene [1]. Currently, ethylene is predominantly produced from petrochemical industry by the steam cracking of naphtha and gas oil at high operation temperatures of 750–900 °C [2], which remains problematic due to its high energy demand, complex thermal management [2], [3], and the ever-increasing global depletion of crude oil. In this context, the oxidative dehydrogenation of ethane (ODE) is considered to be an appealing alternative route to produce ethylene [4], [5], [6], [7], benefiting from the following advantages: lower operation temperature in ODE than in steam cracking, coke-free process due to oxygen existence, and particularly, abundant reserves of ethane in shale gas.

Ni-based catalysts are promising candidates for ODE reaction owing to their good catalytic performance at relatively low reaction temperatures [5], [6], [7], [8]. Up to date, most efforts have been devoted to improving the catalytic performance of Ni-based catalysts by modification with various promoters (e.g., ZrO₂ [5], CeO₂ [6] and Nb₂O₅ [7]) and/or catalyst support screening [9]. For example, a high C₂H₄ yield of 36.3% has been reported to be achievable over a promising NiO/MgO catalyst at 600 °C [9]. Despite the above advances, their practical application still remains particularly challenging. On account of poor heat conductivity of such traditional oxide-supported NiO catalysts, the strong exothermicity of ODE reaction process will unavoidably induce “hotspots” in the reactor bed, which not only is a main cause of catalyst deactivation but is also dangerous in industrial applications. Hence, it is particularly desirable and worthwhile to render a catalyst with unique combination of excellent catalytic performance and enhanced thermal conductivity that is essential to rapidly dissipate the great release of reaction heat from such a strongly exothermic ODE process. To accomplish this goal, ceramic [6] and stainless steel cylinder foams [10] structured catalysts have been recently reported for the ODE process, while the integration of active components onto such monolithic foams involves a dissatisfactory coating process which leads to ill-controlled physic-chemical structure of the coated-catalysts as well as their poor adherence to foam-surface and binder harmful contamination. Unlike the inertness of ceramic and stainless steel foams, Ni-foam is much more chemically active, providing an opportunity for inventing a whole new non-dip-coating way to fabricate foam-structured Ni-based catalysts [11], [12], [13], [14]. For example, NiO-Al₂O₃ composite catalyst layer is in-situ created and firmly embedded onto the Ni-foam struts via the wet chemical etching method, exhibiting excellent catalytic activity/selectivity and stability in syngas methanation [11], [12], [13] and catalytic oxy-methane reforming [14]. Seeing the beneficial features of Ni-foam to the design of structured catalysts, a foam-structured NiPd/Ni-foam catalyst is also developed via galvanic deposition of Pd NPs on Ni-foam [15], which exhibits as-expected low pressure drop and high heat/mass transfer with excellent activity/selectivity and stability for the coalbed methane (CBM) deoxygenation via catalytic combustion of methane.

In present work, a foam-structured CeO₂-NiO-Al₂O₃ catalyst engineered from micro- to macro-scale was developed for the ODE reaction process, which was obtained by chemically etching a Ni-foam to create NiO-Al₂O₃ composite layer on its strut and subsequently adding CeO₂ modifier via impregnation method. This non-dip-coating approach is working effectively and efficiently to endow the highly thermal conductive Ni-foam with promising catalytic performance for the ODE reaction.

Section snippets

Experimental

A NiO-Al₂O₃/Ni-foam catalyst was firstly prepared by the wet chemical etching method [16]. Then, CeO₂ modifier was placed onto the as-prepared NiO-Al₂O₃/Ni-foam samples by impregnation method with cerium nitrate aqueous solution to obtain xCeO₂-NiO-Al₂O₃/Ni-foam catalysts (CeO₂ loading: x = 3, 5, 7, or 10 wt%). For comparison, a particulate catalyst of CeO₂/NiO was also prepared by impregnation method with pure NiO powder as support. The catalysts were characterized by inductively coupled

Geometry, morphology and structural features

Fig. 1 shows the geometry, morphology and structural features of our monolithic CeO₂-NiO-Al₂O₃/Ni-foam catalysts, and Table 1 summarizes their physicochemical and textural properties. The monolithic Ni-foam support (100 pores per inch (PPI); circular chip in 8 mm diameter and 1 mm thickness) possesses 3D open cell structure with 95 vol% void volumes (Fig. S1A and S1B). As shown in Fig. 1A and Fig. S1C, after chemical etching and subsequent calcination the Ni-foam strut surface became rough and was

Conclusions

A foam-structured CeO₂-NiO-Al₂O₃/Ni-foam catalyst has been developed via wet chemical etching of a highly thermal conductive Ni-foam and subsequent modification with CeO₂ additives. This facile non-dip-coating approach is effective and efficient to combine high catalytic performance with enhanced heat/mass transfer, high permeability and unique form factor. Such catalyst is qualified for the ODE reaction with a high ethylene productivity of 425 g_Ethylene kg_cat^− 1 h^− 1 for a feed gas of C₂H₆/O₂/N₂ =

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Structured catalysts have important advantages compared to powder formulations and they are required for processes intensification. In this work, three different ceramic structures: a cordierite monolith, an alumina foam and an alumina-silica paper were used as substrates for the deposition of a NiO-Al₂O₃ coating and tested in the oxidative dehydrogenation of ethane to produce ethylene. For comparison, a NiO-Al₂O₃ powder catalyst was also prepared. Nickel oxide species with different physicochemical features were obtained over each structure, evidenced by morphological (SEM-EDX) and physicochemical characterization (XRD, LRS and XPS). The best distributions of the catalytic coatings and NiO physicochemical properties were obtained when the monolith and the foam were used as substrates. These led to higher NiO-Al₂O₃ interactions and consequently to high ethylene selectivity values, 70–90 %, corresponding to the former an ethane conversion of 22 % and to the latter a 5 %. The distribution of the active phase on the ceramic paper was heterogeneous, with NiO agglomerations and poor NiO-support interaction thus achieving low olefin selectivity (∼ 30 %). The addition of a second element such as cerium was also studied in those structured catalysts with high selectivity, resulting in both cases in an increment of ethane conversion but a decrease in ethylene selectivity. This behavior was attributed to the generation of electrophilic oxygen species.
Dehydrogenation versus hydrogenolysis in the reaction of light alkanes over Ni-based catalysts
2020, Journal of Industrial and Engineering Chemistry
Given the high cost of Pt-based catalysts and the environmental issue of CrO_x-based catalysts in dehydrogenation processes, Ni-based catalysts have been extensively explored as alternatives. In order to take the advantage of the high activation ability of Ni towards alkanes, herein, the reaction behaviors of light alkanes, primarily dehydrogenation versus hydrogenolysis, over Ni-based catalysts have been reviewed and probed. Ni-based catalysts exhibit an extremely high hydrogenolysis activity for light alkanes. Different from the single hydrogenolysis reaction on the surface of Pt, multiple hydrogenolysis of alkane molecules occurs over Ni sites. The successive α-scission of CC bond over Ni sites results in the generation of abundant methane and coke. To selectively activate CH bond of alkanes and prohibit CC bond rupture, one feasible approach is to introduce effective barriers to destroy the aggregated Ni ensembles active for hydrogenolysis. The promoting mechanism of different barriers (S, P, Cu, Sn, etc.) has been summarized and analyzed. The geometric effect of introduced barriers facilitates the dispersion of Ni particles, and electronic effect reduces the desorption energy of olefins and avoids undesired secondary reactions. Among all these catalysts, NiS and NiSn-based catalysts demonstrate the most outstanding dehydrogenation performance and show great potential for industrial applications.
High-performance Ni-foam-structured Nb<inf>2</inf>O<inf>5</inf>–NiO nanocomposite catalyst for oxidative dehydrogenation of shale gas ethane to ethylene: Effects of Nb<inf>2</inf>O<inf>5</inf> loading and calcination temperature
2019, Microporous and Mesoporous Materials
Large-scale shale gas exploitation greatly enriches ethane resources, making the oxidative dehydrogenation of ethane (ODE) to ethylene quite fascinating, but the qualified catalyst presents a grand challenge. A series of Ni-foam-structured MO_x-NiO (M = Li, Mg, Ga, Ce, Zr, Mo, W, Nb) composite oxide catalysts (denoted as MO_x-NiO/Ni-foam) have been developed for the oxidative dehydrogenation of ethane to ethylene (ODE). The catalysts were obtained by hydrothermal growth of NiC₂O₄ onto a Ni-foam (110 PPI) and subsequent impregnation with an M-containing salt aqueous solution and calcination treatment. Among them, the Nb₂O₅–NiO/Ni-foam showed superior catalytic ODE performance over the others. Both Nb₂O₅ loading and calcination temperature showed remarkable impact on the catalytic performance. The modification with suitable amount of Nb₂O₅ was responsible for the significant elimination of non-selective oxygen species thereby leading to remarkable improvement of the ethylene selectivity. The activity and selectivity of the Nb₂O₅–NiO/Ni-foam catalysts are also sensitive to the calcination temperature that can modulate the desorption properties of their lattice oxygen species to a great extent. The most promising Nb₂O₅–NiO/Ni-foam catalyst is the one modified with 5 wt% Nb₂O₅ and calcined at 450 °C, being capable of converting 60% ethane with a 68% ethylene selectivity for a feed of C₂H₆/O₂/N₂ = 1/1/8 at 410 °C and GHSV of 9000 cm³ g⁻¹ h⁻¹ (corresponding to a high ethylene productivity of 0.423 g_C2H4 g_cat⁻¹ h⁻¹).
A green and facile synthesis of Co<inf>3</inf>O<inf>4</inf> monolithic catalyst with enhanced total oxidation of propane performance
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Citation Excerpt :
The former mainly refers to the use of cordierite as support of the catalytic phase, while the latter to the use of stainless steel, metal alloys, metal foams, etc. [7, 8]. Among these metal monoliths, Ni-foam (NF) was found suitable for preparing supported monolithic catalysts [9], and it has been a splendid choice for providing excellent catalytic activity [10, 11]. The most common methods to deposit active ingredients on a monolith are the sol-gel coating and the impregnation methods [12, 13].
A nanoflower-like nickel foam supported Co₃O₄ (Co-NF) monolithic catalyst was synthesized via a green and facile electro-deposition strategy. The optimized Co-NF presents much higher catalytic activity per Co₃O₄ loading, ca. 6.7 × 10⁻⁴ mol/(g_Co3O4·s) at 220 °C and exhibits a lower activation energy of 46 kJ/mol compared with powder Co₃O₄. It also exhibited good stability (e.g. >80% propane conversion) for 40 h at 350 °C and a GHSV of 30,000 mL/(g_cat·h) without any notable decrease. The 3D hierarchical microstructures with interconnected pore channels, the high Co²⁺ content and the weak CoO bond strength of Co-NF-300 s were considered key factors responsible for the good activity and stability in the propane catalytic total oxidation.
Hollow urchin-like NiO/NiCo<inf>2</inf>O<inf>4</inf> heterostructures as highly efficient catalysts for selective oxidation of styrene
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Size, morphology and microstructure of these solid materials have remarkable effect on their properties and ultimate performances in applications, as the differences in size, morphology and microstructure may result in different electronic and surface properties [1,11–15]. In heterogeneous catalysis, the reaction kinetics is highly dependent on the electronic properties and surface area and porosity of the catalysts [1,13–18]. Therefore, catalyst materials with controlled size, morphology and microstructure have been intensively studied [19–23].
Three-dimensional (3D) hierarchical hollow urchin-like NiO/NiCo₂O₄ heterostructures have been prepared via a facile one-pot hydrothermal method. The 3D urchin-like structure brings about high specific surface area of 40.2 m² g⁻¹. The NiO/NiCo₂O₄ heterostructures are composed of 59 wt% of NiO and 41 wt% of NiCo₂O₄ and enriched with NiO-NiCo₂O₄ phase boundaries. When used as catalysts for styrene oxidation reaction (SOR), the NiO/NiCo₂O₄ heterostructures present a markedly high selectivity of 90.8% to styrene oxide (SO) and a high SO yield of 81.4%. The high catalytic performance of the NiO/NiCo₂O₄ heterostructures can be attributed to the high specific surface area and the abundant NiO-NiCo₂O₄ phase boundaries, both of which contribute to the numerous active sites.
Oxidative dehydrogenation of ethane to ethylene: A promising CeO<inf>2</inf>-ZrO<inf>2</inf>-modified NiO-Al<inf>2</inf>O<inf>3</inf>/Ni-foam catalyst
2018, Applied Catalysis A: General
Citation Excerpt :
The above results indicated that co-modifying with CeO2 and ZrO2 indeed synergistically tamed NiO species to be more selectively active for the ODE reaction. Whereas 3CeO2-5ZrO2-NANF and 5CeO2-5ZrO2-NANF, as well as the 7CeO2-NANF catalysts reported in our previous study [46] achieved ethane conversion higher than the 1CeO2-5ZrO2-NANF at 300–450 °C, no better ethylene yield was obtainable because of their relatively poor selectivity (given that the excess of CeO2 favors the deep oxidation of ethylene at high temperature) (Figs. Fig. 33 and S4). Furthermore, the pristine activity of the CeO2-ZrO2-NANF catalysts is remarkably improved, evidenced by the higher TOFs at 350 °C ranged from 59 to 93 h−1 than that of 38 h−1 for the NANF base catalyst (Table 1).
From macro- to nano-engineering of a promising CeO₂-ZrO₂-doped NiO-Al₂O₃/Ni-foam catalyst has been demonstrated for the oxidative dehydrogenation of ethane to ethylene (ODE), through facial wet chemical etching of a Ni-foam followed post modification with CeO₂ and ZrO₂. The NiO-Al₂O₃/Ni-foam (denoted as NANF) achieved a high ethane conversion of 25.2% but with a very low ethylene selectivity of 43.1% at 450 °C. ZrO₂-doping of the NANF led to a remarkable improvement in the ethylene selectivity but serious deterioration of activity while the CeO₂-doping showed an opposite effect. Co-doping of the NANF using optimal amount of CeO₂ and ZrO₂ markedly promoted not only the activity but also the selectivity to ethylene. For example, over the 1CeO₂-5ZrO₂-NANF (CeO₂:1 wt%, ZrO₂:5 wt%) catalyst, a high ethane conversion of 40.3% was obtained with a 60.6% ethylene selectivity for a feed gas of C₂H₆/O₂/N₂ = 1/1/8 at 500 °C and a gas hourly space velocity of 18,000 cm³ g⁻¹ h⁻¹, corresponding to a high ethylene productivity of 510 g_Ethylene kg_cat⁻¹ h⁻¹. In nature, co-doping with CeO₂ and ZrO₂ synergistically tamed the NiO for selective H-abstraction of the ethane molecules other than over oxidation of them.

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Short communicationMicrostructured CeO2-NiO-Al2O3/Ni-foam catalyst for oxidative dehydrogenation of ethane to ethylene

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental

Geometry, morphology and structural features

Conclusions

Energy

J. Catal.

Appl. Surf. Sci.

Catal. Commun.

J. Catal.

Appl. Catal. A

Catal. A

Appl. Catal., A

Appl. Catal. A

Catal. Commun.

Short communication
Microstructured CeO₂-NiO-Al₂O₃/Ni-foam catalyst for oxidative dehydrogenation of ethane to ethylene