A study is conducted to demonstrate catalytic dehydrogenation of light alkanes on metals and metal oxides. The study provides a complete overview of the materials used to catalyze this reaction, as dehydrogenation for the production of light olefins has become extremely relevant. Relevant factors, such as the specific nature of the active sites, as well as the effect of support, promoters, and reaction feed on catalyst performance and lifetime, are discussed for each catalytic Material. The study compares different catalysts in terms of the reaction mechanism and deactivation pathways and catalytic performance. The duration of the dehydrogenation step depends on the heat content of the catalyst bed, which decreases rapidly due to the endothermic nature of the reaction. Part of the heat required for the reaction is introduced to the reactors by preheating the reaction feed, additional heat being provided by adjacent reactors that are regenerating the coked catalysts.

Catalytic dehydrogenation of light alkanes on metals and metal oxides.

The selective activation and transformation of alkanes or aromatics have been a research goal for several decades.1-3 Today, research in this area is strongly motivated by the need to optimize resources and to shorten the number of steps, hence the direct and selective transformation of petrochemicals into valuable products is therefore of major interest. Any of these processes will have first to rely on the selective C-H bond activation. This has been the holy grail in molecular organometallic chemistry and homogeneous catalysis for some years;1,4,5 several success stories have appeared in the past ten years,6-9 including progress in the direct catalytic functionalization of methane into methanol.10-13 However, finding stable catalytic systems using acceptable operating conditions remains a challenge. In heterogeneous catalysis, several large scale industrial processes are based on the selective C-H bond activation of alkanes and lead to the synthesis of more valuable and functionalized products in a single step, for instance the direct oxidation of butane into maleic anhydride,14-16 the dehydrogenation of propane into propene,17,18 or the direct transformation of liquefied petroleum gas (LPG) into aromatics.19-24 C-H bond activation is in fact a ubiquitous process in heterogeneous catalysis. It involves various types of mechanisms and intermediates. C-H bond activation involving carbonium and carbenium ion intermediates3,25-27 or taking place on metal particles (supported or not) or clean metal surfaces28-35 has been extensively reviewed in the past years. Here, we will focus on processes involving C-H bond activation of alkanes and aromatics on isolated metal centers of surfaces on oxide materials leading to organometallic species and/or intermediates. The review is divided into two main sections focusing on the C-H bond activation on oxide materials and related systems (section 2) and on well-defined organometallic complexes supported on oxide materials (section 3). Section 2 is subdivided into four parts describing C-H bond activation on bulk oxides, bulk metal halides, supported transition-metal oxides, and metal-exchange zeolites.

C−H Bond Activation and Organometallic Intermediates on Isolated Metal Centers on Oxide Surfaces

As a promising approach for carbon dioxide capture, chemical looping combustion has been extensively investigated for more than two decades. However, the chemical looping strategy can be and has been extended well beyond carbon capture. In fact, significant impacts on emission reduction, energy conservation, and value-creation can be anticipated from chemical looping beyond combustion (CLBC). This article aims to demonstrate the versatility and transformational benefits of CLBC. Specifically, we focus on the use of oxygen carriers or redox catalysts for chemical production – a $4 trillion industry that consumes 40.9 quadrillion BTU of energy. Compared to state-of-the-art chemical production technologies, we illustrate that chemical looping offers significant opportunities for process intensification and exergy loss minimization. In many cases, an order of magnitude reduction in energy consumption and CO2 emission can be realized without the needs for carbon dioxide capture. In addition to providing various CLBC examples, this article elaborates on generalized design principles for CLBC, potential benefits and pitfalls, as well as redox catalyst selection, design, optimization, and redox reaction mechanism.

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Chemical looping beyond combustion – a perspective

Dehydrogenation of propane to propene over different polymorphs of gallium oxide

The utilization of CO2 as a soft oxidant and promoter is a promising concept for industrial applications that could not only contribute to the mitigation of CO2 levels, but also the development of economical and energy efficient syntheses of various chemicals. The abundant availability, non-toxic, economic and mild oxidizing properties of CO2 has resulted in immense interest in its use as an oxidant in several reactions, such as the oxidative coupling of CH4 and the oxidative dehydrogenation of alkanes and alkyl aromatics. At present, only a few processes based on CO2 as a soft oxidant have been realised on a technical scale in spite of dedicated research. This review is intended to trace the emergence, application and understanding of such systems and shed light on the further development that may lead to industrial scale operations in the near future.

Carbon dioxide utilization as a soft oxidant and promoter in catalysis

Role of carbon dioxide in the dehydrogenation of ethane over gallium-loaded catalysts

A possibility of antimony oxide as a catalyst for the selective oxidation of methane with oxygen to formaldehyde was investigated. The activity measurement was carried out at an atmospheric pressure and at 873 K, where the homogeneous gas-phase reaction was negligible. Oxidized diamond (O-Dia)-supported antimony oxide catalyst produced 1.3 mmol h −1  g-cat −1 of formaldehyde with a formaldehyde selectivity of 23%. On the other hand, SiO 2 supported antimony oxide catalyst exhibited negligible catalytic activity. XRD and UV–vis analyses revealed that α-Sb 2 O 4 was formed on the oxidized diamond while Sb 6 O 13 was formed on SiO 2 . Selective oxidation of methane to formaldehyde seemed to proceed on α-Sb 2 O 4 with moderate activity and selectivity to formaldehyde, via a redox cycle of α-Sb 2 O 4 and Sb 2 O 4−x . On the other hand, Sb 6 O 13 on SiO 2 was stable under the reaction conditions and the selective oxidation occurred only slightly.

Selective oxidation of methane to formaldehyde over antimony oxide-loaded catalyst

The possibility of CO2 as an alternative oxidant for the direct conversion of CH4 to formaldehyde was investigated. The activity of the catalyst was measured at an atmospheric pressure and temperatures at which the homogeneous gas-phase reactions were negligible. Among various metal oxides loaded on SiO2 catalysts, only vanadium oxide produced the desired product. V2O5/SiO2 and V2O5/oxidized diamond catalysts, the most effective catalysts for formaldehyde synthesis, afforded about 500 μmol h−1 g-cat−1 and 300 μmol h−1 g-cat−1 of formaldehyde at 973 K, respectively. When the reaction of CH4 was carried out in Ar atmosphere, both of the V2O5/SiO2 and V2O5/oxidized diamond catalysts lost the catalytic activity as soon as the lattice oxygen of vanadium oxide was consumed. However, the activity recovered by switching the atmosphere from Ar to CO2. These results strongly suggest that CO2 acts as an oxidant for selective oxidation of CH4 to formaldehyde via the lattice oxygen of vanadium oxide.

Direct formation of formaldehyde from methane and carbon dioxide over vanadium oxide catalysts

Carbon dioxide is an effective oxidant for the conversion of alkanes to chemical feedstocks. Oxidized diamond is useful as a novel catalytic support material. Oxidized diamond provided catalytic sites for the activation of alkanes under CO2 atmosphere. The present findings also suggest that the surface-properties of oxidized diamond may facilitate unique catalytic reactions, such as alkanes conversion in the presence of CO2.

Kimito Okumura

Papers

Role of carbon dioxide in the dehydrogenation of ethane over gallium-loaded catalysts

Selective oxidation of methane to formaldehyde over antimony oxide-loaded catalyst

Direct formation of formaldehyde from methane and carbon dioxide over vanadium oxide catalysts

Novel Selective Oxidation of Light Alkanes Using Carbon Dioxide. Oxidized Diamond as a Novel Catalytic Medium

Novel Selective Oxidation of Light Alkanes Using Carbon Dioxide. Oxidized Diamond as a Novel Catalytic Medium.