Carbon Overcoating of Supported Metal Catalysts for Improved Hydrothermal Stability
16 Jun 2015-
TL;DR: In this paper, carbon overcoats are synthesized at mild temperatures, resulting in an open structure, as revealed by 13C NMR, which helps explain why the over-coats do not significantly block the active sites.
Abstract: Commercial mesoporous oxides, such as silica, are not stable in liquid-phase reactions, particularly aqueous-phase reactions at elevated temperatures, which are corrosive to oxide supports. We have shown previously that the hydrothermal stability of silica is significantly improved by coating the surface with thin carbon layers. Herein, we show that controlled pyrolysis of sugars also provides a facile approach for coating supported metal catalysts, leading to improved dispersion of the active metal phase in the hydrothermally aged catalyst. The carbon overcoats are synthesized at mild temperatures, resulting in an open structure, as revealed by 13C NMR, which helps explain why the overcoats do not significantly block the active sites. We compare two approaches–depositing Pd on carbon-coated silica and depositing carbon overcoats on Pd/silica. The carbon overcoating approach leads to better performance after hydrothermal aging, as determined by using a probe reaction (CO oxidation) to quantify the number ...
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TL;DR: In this article , an encapsulated nickel in a hollow carbon sphere was constructed to effectively catalyze an aqueous-phase hydrogenation-rearrangement tandem (AP-HRT) reaction, in which water was employed as the solvent and reactant simultaneously.
Abstract: As green chemistry, aqueous-phase reactions play a vital role in modern fine chemical synthesis. Herein, an encapsulated nickel in a hollow carbon sphere ([email protected]) catalyst was constructed to effectively catalyze an aqueous-phase hydrogenation-rearrangement tandem (AP-HRT) reaction, in which water was employed as the solvent and reactant simultaneously. The activity is relevant to the HCS and Ni loading. The optimal [email protected] catalyst can release 100% furfural conversion and 99.1% cyclopentanone selectivity at 150 °C and can maintain its activity after 10 cycles of experiments. The superior catalytic performance comes from the fact that each independent [email protected] can be treated as an individual nanoreactor with a void-confinement effect, which not only reduces the side reactions due to the size-selective effect but also prevents active metal from leaching under harsh conditions. The reaction mechanism of FAL AP-HRT was further investigated via kinetic experiments combined with DFT calculations.
14 citations
TL;DR: In this article , the authors introduced titanium into ceria to tune the properties of ceria-supported Ru catalysts for ammonia synthesis, and the result shows that the ammonia synthesis rate of Ru catalyst exhibits a volcanic trend with an increase of titanium content.
10 citations
TL;DR: In this article , the authors highlight studies on catalyst deactivation and mitigation for thermo-catalytic processes in biomass conversion, with emphasis on the deactivation of heterogeneous catalysts caused by the three unique characteristics of biomass-derived feedstocks.
Abstract: Biofuel or biochemical production from biomass, especially lignocellulosic biomass, is the most promising option to replace fossil-based products to achieve sustainability. However, biomass is currently under-utilized because biomass conversion technologies have faced significant challenges to compete with incumbent petroleum technologies. Advancement in catalysis plays a central role in increasing the readiness of biomass conversion technologies. In this respect, improving catalyst stability is one of the well-known grand challenges for biomass conversion catalysis, which impedes the scaling up and commercialization of many biomass conversion techniques. In comparison to conventional processing of fossil fuels (petroleum, coal, and natural gas), biomass conversion is largely challenged by three unique properties of biomass-derived feedstocks─high water and oxygen content, high contamination by minerals and heteroatoms, and high degree and reactivity of oxygen functionalization─which all cause greater catalyst deactivation in different ways. Therefore, research on catalyst deactivation mitigation and catalyst regeneration is extremely important for the development of biomass conversion technologies. This review aims to highlight studies on catalyst deactivation and mitigation for thermo-catalytic processes in biomass conversion, with emphasis on the deactivation of heterogeneous catalysts caused by the three unique characteristics of biomass-derived feedstocks. This work will provide information on correlating the characteristics of biomass-derived streams, their potential impact on catalyst lifetime, and a potential mitigation approach, which could guide a more rational design of a robust catalyst and processes for biomass conversion.
8 citations
TL;DR: In this article , a series of ruthenium catalysts for hydrogenation of l-arabinose/d-galactose sugar mixture were synthesized and their performance was compared to the already known Ru/activated carbon commercial catalyst.
Abstract: This study deals with the production and activation of biochars and their use as supports for a series of ruthenium catalysts for hydrogenation of l-arabinose/d-galactose sugar mixture. The synthesized biochars differ in physicochemical properties and surface chemistry influencing ruthenium metal uptake and dispersion and as a consequence its catalytic behaviour. Selectivity exceeding 95% was observed for both hexitols. The catalytic performance of the prepared Ru supported catalysts is also compared to the already known Ru/activated carbon commercial catalyst.
3 citations
Dissertation•
09 Nov 2017
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TL;DR: Hydrogen Production by Water−Gas Shift Reaction 4056 4.1.
Abstract: 1.0. Introduction 4044 2.0. Biomass Chemistry and Growth Rates 4047 2.1. Lignocellulose and Starch-Based Plants 4047 2.2. Triglyceride-Producing Plants 4049 2.3. Algae 4050 2.4. Terpenes and Rubber-Producing Plants 4052 3.0. Biomass Gasification 4052 3.1. Gasification Chemistry 4052 3.2. Gasification Reactors 4054 3.3. Supercritical Gasification 4054 3.4. Solar Gasification 4055 3.5. Gas Conditioning 4055 4.0. Syn-Gas Utilization 4056 4.1. Hydrogen Production by Water−Gas Shift Reaction 4056
7,067 citations
TL;DR: Corma et al. as mentioned in this paper used the Dupont Award on new materials (1995), and the Spanish National Award “Leonardo Torres Quevedo” on Technology Research (1996) on technology research (1996), to recognize the performance of zeolites as catalysts for oil refining and petrochemistry.
Abstract: It is possible to say that zeolites are the most widely used catalysts in industry They are crystalline microporous materials which have become extremely successful as catalysts for oil refining, petrochemistry, and organic synthesis in the production of fine and speciality chemicals, particularly when dealing with molecules having kinetic diameters below 10 A The reason for their success in catalysis is related to the following specific features of these materials:1 (1) They have very high surface area and adsorption capacity (2) The adsorption properties of the zeolites can be controlled, and they can be varied from hydrophobic to hydrophilic type materials (3) Active sites, such as acid sites for instance, can be generated in the framework and their strength and concentration can be tailored for a particular application (4) The sizes of their channels and cavities are in the range typical for many molecules of interest (5-12 A), and the strong electric fields2 existing in those micropores together with an electronic confinement of the guest molecules3 are responsible for a preactivation of the reactants (5) Their intricate channel structure allows the zeolites to present different types of shape selectivity, ie, product, reactant, and transition state, which can be used to direct a given catalytic reaction toward the desired product avoiding undesired side reactions (6) All of these properties of zeolites, which are of paramount importance in catalysis and make them attractive choices for the types of processes listed above, are ultimately dependent on the thermal and hydrothermal stability of these materials In the case of zeolites, they can be activated to produce very stable materials not just resistant to heat and steam but also to chemical attacks Avelino Corma Canos was born in Moncofar, Spain, in 1951 He studied chemistry at the Universidad de Valencia (1967−1973) and received his PhD at the Universidad Complutense de Madrid in 1976 He became director of the Instituto de Tecnologia Quimica (UPV-CSIC) at the Universidad Politecnica de Valencia in 1990 His current research field is zeolites as catalysts, covering aspects of synthesis, characterization and reactivity in acid−base and redox catalysis A Corma has written about 250 articles on these subjects in international journals, three books, and a number of reviews and book chapters He is a member of the Editorial Board of Zeolites, Catalysis Review Science and Engineering, Catalysis Letters, Applied Catalysis, Journal of Molecular Catalysis, Research Trends, CaTTech, and Journal of the Chemical Society, Chemical Communications A Corma is coauthor of 20 patents, five of them being for commercial applications He has been awarded with the Dupont Award on new materials (1995), and the Spanish National Award “Leonardo Torres Quevedo” on Technology Research (1996) 2373 Chem Rev 1997, 97, 2373−2419
5,290 citations
TL;DR: Dehydroisomerization of Limonene and Terpenes To Produce Cymene 2481 4.2.1.
Abstract: 3.2.3. Hydroformylation 2467 3.2.4. Dimerization 2468 3.2.5. Oxidative Cleavage and Ozonolysis 2469 3.2.6. Metathesis 2470 4. Terpenes 2472 4.1. Pinene 2472 4.1.1. Isomerization: R-Pinene 2472 4.1.2. Epoxidation of R-Pinene 2475 4.1.3. Isomerization of R-Pinene Oxide 2477 4.1.4. Hydration of R-Pinene: R-Terpineol 2478 4.1.5. Dehydroisomerization 2479 4.2. Limonene 2480 4.2.1. Isomerization 2480 4.2.2. Epoxidation: Limonene Oxide 2480 4.2.3. Isomerization of Limonene Oxide 2481 4.2.4. Dehydroisomerization of Limonene and Terpenes To Produce Cymene 2481
5,127 citations
TL;DR: An overview of chemical catalytic transformations of biomass-derived oxygenated feedstocks in the liquid phase to value-added chemicals and fuels is presented, with specific examples emphasizing the development of catalytic processes based on an understanding of the fundamental reaction chemistry.
Abstract: Biomass has the potential to serve as a sustainable source of energy and organic carbon for our industrialized society. The focus of this Review is to present an overview of chemical catalytic transformations of biomass-derived oxygenated feedstocks (primarily sugars and sugar-alcohols) in the liquid phase to value-added chemicals and fuels, with specific examples emphasizing the development of catalytic processes based on an understanding of the fundamental reaction chemistry. The key reactions involved in the processing of biomass are hydrolysis, dehydration, isomerization, aldol condensation, reforming, hydrogenation, and oxidation. Further, it is discussed how ideas based on fundamental chemical and catalytic concepts lead to strategies for the control of reaction pathways and process conditions to produce H(2)/CO(2) or H(2)/CO gas mixtures by aqueous-phase reforming, to produce furan compounds by selective dehydration of carbohydrates, and to produce liquid alkanes by the combination of aldol condensation and dehydration/hydrogenation processes.
2,063 citations
TL;DR: Methods for the preparation of mesoporous carbon materials with extremely high surface areas and ordered mesostructures, with potential applications as catalysts, separation media, and advanced electronic materials in many scientific disciplines are developed.
Abstract: Porous carbon materials are of interest in many applications because of their high surface area and physicochemical properties. Conventional syntheses can only produce randomly porous materials, with little control over the pore-size distributions, let alone mesostructures. Recent breakthroughs in the preparation of other porous materials have resulted in the development of methods for the preparation of mesoporous carbon materials with extremely high surface areas and ordered mesostructures, with potential applications as catalysts, separation media, and advanced electronic materials in many scientific disciplines. Current syntheses can be categorized as either hard-template or soft-template methods. Both are examined in this Review along with procedures for surface functionalization of the carbon materials obtained.
1,716 citations