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Journal ArticleDOI

Hydrogen production from ethanol reforming: Catalysts and reaction mechanism

TL;DR: A detailed analysis based on the spectroscopic technique revealed that reaction pathways proceeded along a mono-functional or bi-functional mechanism according to the types of active metal and support as mentioned in this paper.
Abstract: Hydrogen production from ethanol is regarded as a promising way for energy sustainable development, which is undergoing an explosive growth over the last decade. Besides operating conditions, hydrogen yield greatly dependent on the nature of metal and the support selected. To date, Rh based catalysts proved to be the most active systems due to the fact that Rh possessed the greatest capacity toward C–C bond cleavage. Support also played a critical role in terms of hydrogen selectivity and stability. MgO, CeO2 and La2O3 etc were evidenced as suitable supports because of their basic characteristic and/or redox capacity. A detailed analysis based on the spectroscopic technique revealed that reaction pathways proceeded along a mono-functional or bi-functional mechanism according to the types of active metal and support. Ethanol dehydrogenation and/or dehydration reaction mainly occurred on the support, and the diffusion/transformation of the intermediates took place at the metal–support interface. Meanwhile, active metal accelerated the decomposition reaction. The observed catalyst deactivation was normally assigned to the coke formation, active metal sintering and/or oxidation as well as the impurity in crude bio-ethanol. Hence, the scope of this review is to address the present progress in ethanol reforming for hydrogen production including catalyst development and the analysis of the reaction mechanism and kinetics in order to shed light on the design of high efficient catalyst systems and the fundamental understanding of ethanol conversion at the molecular level.
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TL;DR: In this article, a review deals with the currently existing alternatives at the catalyst and reactor level to cope with catalyst deactivation and increase process stability, and then delves with the fundamental phenomena occurring during this catalysts deactivation.
Abstract: Undoubtedly, hydrogen (H2) is a clean feedstock and energy carrier whose sustainable production should be anticipated. The pyrolysis of biomass or waste plastics and the subsequent reforming over base (transition) or noble metals supported catalysts allows reaching elevated H2 yields. However, the catalyst used in the reforming step undergoes a rapid and severe deactivation by means of a series of physicochemical phenomena, including metal sintering, metallic phase oxidation, thermal degradation of the support and, more notoriously, coke deposition. This review deals with the currently existing alternatives at the catalyst and reactor level to cope with catalyst deactivation and increase process stability, and then delves with the fundamental phenomena occurring during this catalyst deactivation. An emphasis is placed on coke deposition and its influence on deactivation, which depends on its location, chemical nature, morphology, precursors or formation mechanism, among others. We also discuss the challenges for increasing the value of the carbon materials formed and therefore, enhance process viability.

248 citations

Journal ArticleDOI
TL;DR: In insights into the intrinsic mechanism involved in catalytic reforming are presented and guidance is provided to the development of novel catalysts and processes for the efficient utilization of oxygenates for energy and environmental purposes.
Abstract: This Review describes recent advances in the design, synthesis, reactivity, selectivity, structural, and electronic properties of the catalysts for reforming of a variety of oxygenates (e.g., from simple monoalcohols to higher polyols, then to sugars, phenols, and finally complicated mixtures like bio-oil). A comprehensive exploration of the structure–activity relationship in catalytic reforming of oxygenates is carried out, assisted by state-of-the-art characterization techniques and computational tools. Critical emphasis has been given on the mechanisms of these heterogeneous-catalyzed reactions and especially on the nature of the active catalytic sites and reaction pathways. Similarities and differences (reaction mechanisms, design and synthesis of catalysts, as well as catalytic systems) in the reforming process of these oxygenates will also be discussed. A critical overview is then provided regarding the challenges and opportunities for research in this area with a focus on the roles that systems of ...

237 citations

Journal ArticleDOI
TL;DR: The theoretical basis behind carbon and sulfur poisoning is studied, before examining the strategies toward carbon and sulphur tolerance used so far in the SOFC literature, and the more extensive relevant heterogeneous catalysis literature is studied for strategies and materials which could be incorporated intocarbon and sulfur tolerant fuel cells.
Abstract: Solid oxide fuel cells (SOFCs) are a rapidly emerging energy technology for a low carbon world, providing high efficiency, potential to use carbonaceous fuels, and compatibility with carbon capture and storage. However, current state-of-the-art materials have low tolerance to sulfur, a common contaminant of many fuels, and are vulnerable to deactivation due to carbon deposition when using carbon-containing compounds. In this review, we first study the theoretical basis behind carbon and sulfur poisoning, before examining the strategies toward carbon and sulfur tolerance used so far in the SOFC literature. We then study the more extensive relevant heterogeneous catalysis literature for strategies and materials which could be incorporated into carbon and sulfur tolerant fuel cells.

220 citations

Journal ArticleDOI
TL;DR: Magnesium hydroxide and magnesium oxide are compounds with favorable and unique properties, leading to a broad range of opportunities for their use in science, and above all in practical applications.

206 citations

Journal ArticleDOI
TL;DR: In this article, the authors have discussed the necessity of employing hydrogen as an alternative fuel, its production paths, storage issues, transportation and the available sources in Asia, and highlighted the challenges in the execution of hydrogen as a economical fuel in Asia.
Abstract: Renewable alternative energy sources are getting more attention due to the depleting nature of non-renewable fossil fuels. Increasing global warming, caused by the combustion of fossil fuels, triggered the intense research in finding out better energy options with low emission. Among the potential energy options, hydrogen is a clean fuel candidate as it simply produces water as byproducts when burning. Hydrogen can be generated from different renewable sources and Asia is one of the continents which is rich in renewable energy resources. The resources, safety parameters, public acceptability, and proper government incentives are the major factors affecting the implementation of hydrogen as an economical energy source in Asian countries. The present review deals with the necessity of employing hydrogen as an alternative fuel, its production paths, storage issues, transportation and the available sources. Special emphasis has been given to the discussion of renewable hydrogen economy in some Asian countries like, Japan, Korea, China, India and Malaysia. The challenges in the execution of hydrogen as an economical fuel in Asia are also highlighted.

205 citations

References
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Journal ArticleDOI
TL;DR: In this article, the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production is reviewed, based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range.
Abstract: Nano-sized TiO 2 photocatalytic water-splitting technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy. Presently, the solar-to-hydrogen energy conversion efficiency is too low for the technology to be economically sound. The main barriers are the rapid recombination of photo-generated electron/hole pairs as well as backward reaction and the poor activation of TiO 2 by visible light. In response to these deficiencies, many investigators have been conducting research with an emphasis on effective remediation methods. Some investigators studied the effects of addition of sacrificial reagents and carbonate salts to prohibit rapid recombination of electron/hole pairs and backward reactions. Other research focused on the enhancement of photocatalysis by modification of TiO 2 by means of metal loading, metal ion doping, dye sensitization, composite semiconductor, anion doping and metal ion-implantation. This paper aims to review the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production. Based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range. Therefore, they play an important role in the development of efficient photocatalytic hydrogen production.

3,714 citations

Journal ArticleDOI
TL;DR: The literature treating mechanisms of catalyst deactivation is reviewed in this paper, which can be classified into six distinct types: (i) poisoning, (ii) fouling, (iii) thermal degradation, (iv) vapor compound formation accompanied by transport, (v) vapor solid and/or solid solid reactions, and (vi) attrition/crushing.
Abstract: The literature treating mechanisms of catalyst deactivation is reviewed. Intrinsic mechanisms of catalyst deactivation are many; nevertheless, they can be classified into six distinct types: (i) poisoning, (ii) fouling, (iii) thermal degradation, (iv) vapor compound formation accompanied by transport, (v) vapor-solid and/or solid-solid reactions, and (vi) attrition/crushing. As (i), (iv), and (v) are chemical in nature and (ii) and (v) are mechanical, the causes of deactivation are basically three-fold: chemical, mechanical and thermal. Each of these six mechanisms is defined and its features are illustrated by data and examples from the literature. The status of knowledge and needs for further work are also summarized for each type of deactivation mechanism. The development during the past two decades of more sophisticated surface spectroscopies and powerful computer technologies provides opportunities for obtaining substantially better understanding of deactivation mechanisms and building this understanding into comprehensive mathematical models that will enable more effective design and optimization of processes involving deactivating catalysts. © 2001 Elsevier Science B.V. All rights reserved.

2,526 citations

Journal ArticleDOI
TL;DR: In this article, structural and electronic properties and energetic quantities related to the formation of oxygen defects at transition metal (TM) and rare earth (RE) oxide surfaces, neutral oxygen vacancies in particular, play a major role in a variety of technological applications.

1,078 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed the development of bimetallic catalysts, alloy catalysts and double-bed reactors to enhance hydrogen production and long-term catalysts stability.

1,072 citations

Journal ArticleDOI
TL;DR: In this paper, an overview of these technologies for hydrogen production from biomass is presented. And the future development will also be addressed, as well as future development of the future technologies.

1,065 citations