Considering the expansion of the use of renewable energy in the future, the technology to store and transport hydrogen will be important. Hydrogen is gaseous at an ambient condition, diffuses easily, ...and its energy density is low. So liquid organic hydrogen carriers (LOHCs) have been proposed as a way to store hydrogen in high density. LOHC can store, transport, and use hydrogen at high density by hydrogenation and dehydrogenation cycles. In this review, we will focus on typical LOHCs, methylcyclohexane (MCH), 18H-dibenzyltoluene (DBT), and 12H-N-ethylcarbazole (NECZ), and summarize recent developments in dehydrogenation catalytic processes, which are key in this cycle.
Ethanol steam reforming (ESR) is a promising reaction as a sustainable, carbon-neutral hydrogen production process. Because of their high activity and low cost, Co-based and Ni-based catalysts are ...suitable for industrial ESR processes. Nevertheless, these catalysts present several issues, such as deactivation by coke formation and methane formation as a by-product. This review summarizes the most recent three years works related to ESR for hydrogen production over non-noble transition metal catalysts, exploring their catalytic performance, coke formation, and reaction mechanisms, to provide direction for the development of high-performance catalysts. Findings suggest the particle size and oxidation state of the active metal, acid–base and redox properties of the support, and appropriate promoter selection as important factors to minimize coke and by-product formation.
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•Ethanol steam reforming (ESR) is a promising candidate for renewable H2 production.•Supported Ni or Co catalyst with small metal particle is suitable for efficient ESR.•Basic support or promoter contributes to suppress coke formation during ESR.•Redox active support with oxygen storage capacity contributes to removal of coke.
Recent trends on the direct conversion of methane, employing carbon dioxide as an oxidizing agent are reviewed. While oxidation using molecular oxygen involves the sequential oxidation of various ...intermediates to generate carbon dioxide and exhibits low selectivity for the desired products, methane activation using carbon dioxide as an oxidant eliminates this sequential oxidation and has considerable promise. In this context, supported metal catalysts can promote the dry reforming of methane, and structured oxide catalysts have been found to enable methane coupling to C2 products, using carbon dioxide as the oxidizing agent. This review also summarizes recent research regarding the use of nonconventional processes for methane activation in conjunction with carbon dioxide.
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•Supported metal catalysts such as Ni/oxide materials promote DRM for syngas production.•Perovskites and various oxides which generate active surface oxygen species promote CO2-OCM.•Oxidation by carbon dioxide results in high selectivity for specific products.•Catalytic process in conjunction with plasma or an electric field promotes DRM and CO2-OCM at ambient temperature.
Methane is an important chemical resource, not only in natural gas but also in biogas, which can be regarded as a renewable energy resource. Reforming of methane with steam or carbon dioxide, which ...is important for producing hydrogen and syngas, is conducted at high temperatures using heterogeneous catalysts. To achieve high activity, stability, and low carbon deposition, many studies have been conducted in recent years on the use of alloys as active sites in these catalysts. This review presents a summary of recent studies of alloy catalysts, for which various secondary metals have been added to active metals, such as Ni. Then we summarize the current status of these alloys in terms of their structure, electronic state, and adsorption. The reported effects of alloying include improvement of dispersion and reducibility of the supported metal, change in catalytic performance such as activity and selectivity, and improvement of durability against carbon deposition, sulphur poisoning, and sintering. The directions of future research and development are summarized in terms of sulphur resistance, sintering inhibition, and high activity at low temperatures.
A survey on the catalytic nature of Ni-based alloy catalysts in recent years provides a direction for future catalyst development.
Hydrogen migration over a metal oxide surface is an extremely important factor governing the activity and selectivity of various heterogeneous catalytic reactions. Passive migration of hydrogen ...governed by a concentration gradient is called hydrogen spillover, which has been investigated broadly for a long time. Recently, well-fabricated samples and state-of-the-art measurement techniques such as
operando
spectroscopy and electrochemical analysis have been developed, yielding findings that have elucidated the migration mechanism and novel utilisation of hydrogen spillover. Furthermore, great attention has been devoted to surface protonics, which is hydrogen migration activated by an electric field, as applicable for novel low-temperature catalysis. This article presents an overview of catalysis related to hydrogen hopping, sophisticated analysis techniques for hydrogen migration, and low-temperature catalysis using surface protonics.
An overview of catalysis related to hydrogen spillover, surface protonics, analysis techniques for hydrogen migration, and low-temperature catalysis using surface protonics are summarized.
The process of combining heterogeneous catalysts and direct current (DC) electric fields can achieve high catalytic activities, even under mild conditions (<500 K) with relatively low electrical ...energy consumption. Hydrogen production by steam reforming of methane, aromatics and alcohol, dehydrogenation of methylcyclohexane, dry reforming of methane, and ammonia synthesis are known to proceed at low temperatures in an electric field.
In situ
/
operando
analyses are conducted using IR, Raman, X-ray absorption fine structure, electrochemical impedance spectroscopy, and isotopic kinetic analyses to elucidate the reaction mechanism for these reactions at low temperatures. The results show that surface proton hopping by a DC electric field, called surface protonics, is important for these reactions at low temperatures because of the higher surface adsorbate concentrations at lower temperatures.
We investigate the mechanism behind the high catalytic activities achieved when combining heterogeneous catalysts and direct current electric fields even under mild conditions (<500 K) with relatively low electrical energy consumption.
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•Well-defined Ga- and Mo-modified ZSM-5 catalysts synthesized.•Ga/ZSM-5 and Mo/ZSM-5 active in aromatization of ethane to BTX aromatics.•Kinetic analysis of ethane conversion ...mechanisms.•Ga: ethane dehydrogenation, oligomerization, aromatization.•Mo: radical mechanism with hydrocarbon pool species similar to methane aromatization.
Aromatization of light hydrocarbons can contribute to a secure supply of aromatics for the chemical industry. In this work, we investigate the influence of modification of zeolite ZSM-5 with Ga and Mo on the reaction mechanism underlying the activation and aromatization of ethane. Well-defined Mo/ZSM-5 and Ga/ZSM-5 zeolites efficiently promote ethane aromatization to benzene-toluene-xylene mixtures. Both catalysts suffer from coke formation, which leads to rapid deactivation. From catalytic tests, temperature-programmed surface reaction and pulsed reaction experiments, we infer that ethane conversion on Ga/ZSM-5 follows a conventional sequential dehydrogenation-oligomerization-aromatization mechanism, while the reaction over Mo/ZSM-5 involves reactive surface carbon (hydrocarbon pool) species.
Hypercoal (HPC) is examined as a caking additive to the mixture of strongly coking coal and non-slightly coking coal. Samples were coked, then their strength and crystallinity of the carbon structure ...by Raman spectra were measured. Hypercoal addition increased strength of coke, and a good correlation was observed between the mechanical strength of coke and the Raman parameter defined by the ratio of D3-band to G-band. Results suggest that mutual melting between blended coal and HPC brought strong carbonaceous structure with highly crystallized. The Raman parameter can predict the coke strength to some extent.
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