Authors:Kuo Liu; Alexandre I. Rykov; Junhu Wang; Tao Zhang Pages: 1 - 142 Abstract: Publication date: 2015 Source:Advances in Catalysis, Volume 58 Author(s): Kuo Liu, Alexandre I. Rykov, Junhu Wang, Tao Zhang Mößbauer spectroscopy is a high-resolution spectroscopic technique suitable for investigating solid catalysts that contain nuclei which exhibit the Mößbauer effect. As integral part of a solid, the Mößbauer nucleus plays the role of a probe that interacts, by virtue of its magnetic and electric moments, with the surrounding fields created by unpaired electrons and ionic charges. The Mößbauer effect can be used to quantitatively measure these hyperfine interactions with unprecedented energy resolution, and a series of gamma-resonance techniques are based on this effect. These techniques allow the determination of the catalyst phase, the particle size, the structure, and the oxidation state in the bulk and at the surface of the catalyst, and they provide additional information that is difficult to acquire with other techniques. In this review, the principles of Mößbauer spectroscopy, the observed effects and hyperfine interactions, and in situ techniques are presented in compact form. The search for correlations between catalytic behavior and the structure and composition of catalysts motivate Mößbauer measurements under in situ conditions. The recent advances made by application of Mößbauer spectroscopy in catalysis are summarized in detail, including results from energy catalysis, environmental catalysis, aerospace catalysis, petrochemistry, and photocatalysis. Finally, brief insight into biological catalysis is given by reviewing the latest applications of synchrotron radiation nuclear gamma-resonance elastic and inelastic scattering spectroscopies that have recently been implemented at synchrotron rings of the third generation.
Authors:Eelco T.C. Vogt; Gareth T. Whiting; Abhishek Dutta Chowdhury; Bert M. Weckhuysen Pages: 143 - 314 Abstract: Publication date: 2015 Source:Advances in Catalysis, Volume 58 Author(s): Eelco T.C. Vogt, Gareth T. Whiting, Abhishek Dutta Chowdhury, Bert M. Weckhuysen Zeolite-based catalyst materials are widely used in chemical industry. In this chapter, the applications of zeolites and zeotypes in the catalytic conversion of oil and gas are reviewed. After a general introduction to zeolite science and technology, we discuss refinery applications, such as fluid catalytic cracking and hydrocracking, and also a wide variety of important petrochemical processes, such as alkylation and isomerization. The fields of low-temperature zeolite-assisted methane activation and methanol-to-hydrocarbon conversion are also covered, as well as several zeolite-catalyzed organic reactions with the aim to synthesize fine chemicals and pharmaceutical intermediates. By reviewing the processes, a wide range of catalytic functionalities are discussed, including Brønsted and Lewis acid sites, basic sites as well as metal and redox sites. The chapter continues with a discussion of the effects of zeolite–binder interactions in commercial catalysts, where the zeolite is only part of the system. We show how modern microspectroscopy methods provide detailed insight into the complex structure of these catalyst materials. Finally, we present future directions, which may include new zeolite-based processes for chemicals production or energy conversion, while new synthetic and characterization tools are envisioned to contribute to the accelerated discovery of new zeolite framework structures.
Authors:J.W. Thybaut; G.B. Marin Abstract: Publication date: Available online 10 November 2016 Source:Advances in Catalysis Author(s): J.W. Thybaut, G.B. Marin Hydroisomerization and hydrocracking are widely recognized as versatile reactions. They allow not only converting feeds of various origin and quality into high-value blendstocks but also identifying the opportunities brought about by different solid acids with characteristic framework structures to tailor activity and product selectivity. The bifunctional reaction mechanism is an essential feature in this respect. It comprises acid-catalyzed rearrangement and cracking in addition to metal-catalyzed (de)hydrogenation and is effective at relatively mild operating conditions. Innumerable combinations of metal and acid functions, ranging, respectively, from sulfided transition metals to noble ones and from crystalline, microporous to wider pore, amorphous materials are available for ensuring the required catalytic performance to convert the feed into the desired product slate. An adequate understanding of the detailed reaction mechanism represents a crucial element in this endeavor. Over the years an interesting evolution from simple, lumped model toward advanced ones accounting for all potentially occurring elementary steps could be discerned. Hydrocracking has been among the first reactions involved in hydrocarbon fuel production and regained popularity in the last years because of the processing of ever more heavy crudes. Its horizon, however, extends beyond the fossil era with applications in bio-fuel production and plastic waste valorization. It ensures a bright future for a historical and reliable conversion process.
Authors:C. Paolucci; J.R. Di Iorio; F.H. Ribeiro; R. Gounder; W.F. Schneider Pages: 1 - 107 Abstract: Publication date: Available online 15 November 2016 Source:Advances in Catalysis Author(s): C. Paolucci, J.R. Di Iorio, F.H. Ribeiro, R. Gounder, W.F. Schneider Copper-exchanged, small-pore chabazite (CHA) zeolites were commercialized in 2009 for the selective catalytic reduction (SCR) of NO x compounds with ammonia, as an emissions control strategy in diesel automotive exhaust aftertreatment. Here, we review the fundamental scientific advances that have since been made in the molecular-level understanding of the active sites and mechanisms responsible for NO x SCR with NH3 on Cu-CHA catalysts. A large body of experimental and theoretical characterization has identified that these “single-site” catalysts contain Cu sites of different local coordinations and structures, influenced by synthetic and environmental factors. The speciation of isolated Cu ions is inextricably linked to the support composition and the conditions of exposure. We make new and unifying connections among the seemingly disparate findings of experimental investigations of Cu-CHA catalysts that differ in origin and treatment history, using ex situ and in situ characterizations, and operando characterization during catalysis. We discuss theory-based studies, in conjunction with multiple experimental spectroscopic methods performed on model Cu-CHA catalysts, that provide precise molecular assignments across a wide range of catalysts and conditions. We highlight how molecular-level descriptions of the active sites and mechanisms can provide insight into the chemical factors that influence practical SCR performance and behavior, including the onset of low-temperature NO x conversion, and the critical role of NH3 solvation of Cu active sites for low-temperature activity. Finally, we describe how the fundamental heterogeneous catalysis science approaches used to interrogate Cu-CHA catalysts used for NO x SCR with NH3 can be used to elucidate the molecular-level details of chemistry that occurs on other single-site catalysts.
Authors:Laszlo Nemeth; Simon R. Bare Pages: 1 - 97 Abstract: Publication date: 2014 Source:Advances in Catalysis, Volume 57 Author(s): Laszlo Nemeth , Simon R. Bare Since the discovery of titanium silicalite more than 30 years ago, framework metal-containing zeotype materials have become an important class of catalyst, finding application in several industrial processes. Incorporation of cations of titanium, tin, iron, and other elements into zeotype frameworks (and also into ordered mesoporous materials) has led to both scientific progress and engineering innovations in catalysis. As a result of these developments, framework metal-containing zeotype materials have been implemented in the preceding decade in new commercial, by-product-free green processes, which have improved sustainability in the chemical industry. Based on a comprehensive analysis of the recent literature including patents, this review is a summary of the current knowledge of the science and technology of framework metal-containing zeotype materials. The synthesis of these materials is summarized, followed by an account of state-of-the-art characterization results. The key catalytic chemistries, which can be classified into oxidation reactions such as olefin epoxidation, aromatic hydroxylation and ammoximation, and weak Lewis acid-catalyzed reactions, are discussed. Mechanisms proposed for these transformations are reviewed, together with the theoretical and modeling tools applied in this context. An overview of the technologies associated with the use of framework metal-containing zeotype materials demonstrates how these processes are linked with each other through key chemicals involved.
Authors:Konstantin Hadjiivanov Pages: 99 - 318 Abstract: Publication date: 2014 Source:Advances in Catalysis, Volume 57 Author(s): Konstantin Hadjiivanov Surface hydroxyl groups are active centers in many catalytic reactions and can play an important role during catalyst preparation. In this chapter, the application of infrared spectroscopy for identification and characterization of surface OH groups is reviewed. The potential of other techniques is also briefly described. The vibrational signature of various types of hydroxyls is discussed; however, the amount of information that can be gathered from the hydroxyl spectra itself is limited. In contrast, application of probe molecules allows a profound characterization of hydroxyl species. Two scenarios are considered: the formation of H-bonds between hydroxyl groups and probe molecules, and chemical reactions between hydroxyl groups and molecules or ions (such as protonation of basic probe molecules, exchange reactions, redox processes). Means to explore the accessibility and location of hydroxyl groups are introduced. The properties of OD and OH groups are compared, and the application of H/D exchange as a diagnostic reaction is discussed. Finally, the hydroxyl population on materials of practical interest is analyzed.
Authors:Guido Busca Pages: 319 - 404 Abstract: Publication date: 2014 Source:Advances in Catalysis, Volume 57 Author(s): Guido Busca The published data concerning the structural, surface, and catalytic properties of aluminas are reviewed, and these properties are related to the preparation procedures. The experimental and computational investigations of the structural characteristics of the polymorphs most useful for applications in catalysis, which are γ-, η-, δ-, and θ-Al2O3, are critically analyzed. The thermodynamics of the various polymorphs and the kinetics of the phase transitions are considered. The available information on Brønsted sites (i.e., hydroxyl groups), Lewis acid sites, and acid–base pairs on the surface of aluminas is discussed. Data regarding the application of aluminas as a catalyst and as a catalyst support are summarized. Suggestions for future research are proposed.
Authors:Michel Che; Gerhard Ertl Bruce Gates Konstantin Hadjiivanov Abstract: Publication date: 2014 Source:Advances in Catalysis, Volume 57 Author(s): Michel Che , Gerhard Ertl , Bruce C. Gates , Konstantin Hadjiivanov
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