bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors influencing the incorporation of web technologies by university libraries in Southern African Development Community
Authors: Ndinoshiho Joseph , Nassimbeni Mary
Published: May 2024

The role of web technologies into the service delivery in university libraries cannot be overemphasised. The purpose of this paper was to investigate the factors that influenced the incorporation of web technologies into the services of university libraries in the Southern African Development Community (SADC) region. The study was underpinned by the unified theory of acceptance and use of technology (UTAUT) and triangulated quantitative and qualitative research strategies in data collection and analysis. The population of this study comprised librarians from university libraries in the SADC region whose language of communication is English. A questionnaire, administered with the research electronic data capture (REDCap) software, was employed to collect quantitative data from 54 librarians, while an interview protocol was used to collect qualitative data from 6 librarians. Results showed that university libraries in the SADC region have incorporated web technologies in services. The results further revealed that the UTAUT constructs, namely, performance expectancy, effort expectancy, social influence, and facilitating conditions played a part in decisions by the university libraries to incorporate web technologies into their services and that librarians were influenced by these factors to use such tools to provide web-based library services.
Frequency-specific cortico-subcortical interaction in continuous speaking and listening
Authors: Abbasi Omid , Steingräber Nadine , Chalas Nikos , Kluger Daniel S , Gross Joachim
Published: May 2024

Speech production and perception involve complex neural dynamics in the human brain. Using magnetoencephalography, our study explores the interaction between cortico-cortical and cortico-subcortical connectivities during these processes. Our connectivity findings during speaking revealed a significant connection from the right cerebellum to the left temporal areas in low frequencies, which displayed an opposite trend in high frequencies. Notably, high-frequency connectivity was absent during the listening condition. These findings underscore the vital roles of cortico-cortical and cortico-subcortical connections within the speech production and perception network. The results of our new study enhance our understanding of the complex dynamics of brain connectivity during speech processes, emphasizing the distinct frequency-based interactions between various brain regions.
Severe Kyphosis Patients with Tuberculosis and Chronic Obstructive Pulmonary Disease: A Case Report
Authors: Desdiani Desdiani , Sari Flora Eka
Published: May 2024

Background: Severe kyphosis in advanced age, with a higher incidence observed in women and in elderly males afflicted with pulmonary tuberculosis (TB) and chronic obstructive pulmonary disease (COPD) can pose a significant risk to their overall well-being and potentially endanger their lives.
Methods: A 59-year-old male with respiratory problem, chronic back pain, and walking disorder was admitted to the emergency room with symptoms of shortness of breath that had been worse in the previous three days. According to the patient's mother, the patient's chest had been bent or arched, curved anterior sternum, since he was three years old but had never been referred to a hospital or undergone any medical treatment. Anti-tuberculosis and COPD treatment with physiotherapy during the first 3 months was quite encouraging because now the patient can do light activities and work again.
Results: Delays in spinal correction are caused by a lack of early detection capabilities from an early age and late referral to the hospital. Because of his advanced age, the patient was not able to have thoracic surgery; instead, he received thoracic manual treatment in addition to physiotherapy at a distant facility with restricted surgical capabilities. Rather, physiotherapy, which included thoracic corrective exercises and scapular posture. Correcting thoracic posture, enhancing structural alignment, and increasing thoracic rigidity are the main objectives of this activity.
Conclusion: Patients with severe cases of kyphosis require early detection of bone abnormalities by primary health center staff. Corrections can be made to prevent reduced body function, musculoskeletal disorders, and quality of life.
Effect of Zero Tillage and Different Weed Management Practices in Direct Seeded Rice (Oryza sativa L.) in Indo Gangetic Plains: A Review
Authors: Pradhan Dharani Dhar , Rawal Sandeep , Asif Mo , Behera Swagat Ranjan , Panda Urmila , Simran .
Published: May 2024

Millions of rural and urban residents depend on the rice-wheat cropping system of the Indo-Gangetic plains (IGP) for their food security and means of subsistence. About 18 million hectares (m ha) of rice (Oryza sativa L.) and wheat (Triticum aestivum L.) are rotated across Asia, of which 13.5 m ha are in the Indo-Gangetic Plains (IGP) of India. This agricultural system’s viability is currently in jeopardy due to static yields of both wheat and rice and a decline in total factor productivity. The North West IGP's high input crop culture has allowed weeds to dominate the weed flora, including P. minor in wheat and Echinochloa crus-galli L. in rice. Farmers in North West India have largely used zero tillage for growing wheat, and recently, farmers in the eastern IGP have done the same. Perennial weeds in the Eastern Indo-Gangetic Plain, such Cynodon dactylon L. and Cyperus rotundus L. can occasionally be a nuisance under zero tillage. As an alternative to puddled transplanted rice, the focus is currently on dry direct-seeded rice and machine transplanting of non-puddled rice. As a result of changes in tillage, crop establishment techniques, water use, and weed control brought on by the switch from transplanted rice to direct seeded rice, weed composition and diversity frequently vary. In nations where DSR is frequently used, weedy rice has become a significant concern. Using the Zero Tillage DSR system, certified seed, cultivars that are weed-competitive, stale seedbed procedures, living mulches, and chemical and biological weed control might change weed-crop competition in the crop's favour. However, more research on emergence characteristics and mulching effects of different crop residues on key weeds under zero tillage, cover cropping, and breeding crops for weed suppression will strengthen nonchemical weed management programs. In this review, we examine the extent of weed infestation, weed flora shift and the non-chemical alternative weed management in DSR.
Phosphotriesterase
Authors: Bigley Andrew N , Raushel Frank M
Published: September 2010

Phosphotriesterase (PTE) is a member of the amidohydrolase superfamily with the ability to hydrolyze numerous organophosphate substrates including many insecticides and nerve agents. The native active site metal is zinc, but the enzyme is fully active with a variety of metals. The overall fold of PTE is a (β/α)8TIM‐barrel with the active site located at the C‐terminal end of the barrel. The active site contains the binuclear metal center with the metal ligands being four histidines, an aspartate, and a carboxylated lysine from the C‐terminal ends of the β‐strands. In addition, the metal center contains a bridging hydroxyl that serves as the nucleophile in the SN2‐like reaction. The substrate‐binding site is external to the metal center and is made of residues from the loops connecting the C‐terminal end of each β‐strand to the subsequent α‐helix. The best known substrate for PTE is the insecticide paraoxon, which has a kinetic efficiency that approaches the limits of diffusion. PTE has significant potential as an enzyme tool for the detection and decontamination of pesticides and nerve agents. Numerous variants of PTE have been developed by directed evolution with improved kinetic efficiency toward various organophosphates.
Octaheme CytochromecNitrite Reductase
Authors: Tikhonova Tamara V , Polyakov Konstantin M , Boyko Konstantin M , Safonova Tatiana N , Popov Vladimir O
Published: September 2010

Octaheme cytochromecnitrite reductase (TvNiR) from bacteriumThioalkalivibrio nitratireducenscatalyzes the six‐electron reduction of nitrite and two‐electron reduction of hydroxylamine to ammonium without release of any intermediates. TvNiR also catalyzes the six‐electron reduction of sulfite to sulfide. High‐resolution structures of the TvNiR apo‐form and its complexes with the substrates (nitrite and sulfite) and inhibitors (azide and phosphate) were obtained. The subunit of TvNiR consists of two domains. The N‐terminal domain has a unique fold and contains three hemes. The remaining five hemes are located in the catalytic C‐terminal domain, with the heme arrangement, including the catalytic heme, being identical to that found in pentaheme cytochromecnitrite reductases (ccNiRs). The catalytic machinery of TvNiR resembles that of ccNiRs. It comprises the lysine residue in the proximal position of the catalytic heme, the catalytic triad of tyrosine, histidine, and arginine on the distal side, channels for the substrate and product transport, and two conserved Ca2+‐binding sites. The complete set of eight hemes forms a spatial pattern characteristic of other structurally characterized octaheme cytochromes. In the crystalline state and in solution, TvNiR exists as a stable hexamer containing 48 hemes, which are clustered into three isolated groups, each group comprising 16 interacting hemes.
The Organomercurial LyaseMerB
Authors: Lello Paola Di , Lafrance‐Vanasse Julien , Omichinski James G
Published: September 2010

Mercury is introduced into the environment either from natural occurrences or from human activities, and consumption of mercury‐contaminated fish poses a serious human health issue. The three inorganic forms of mercury are elemental mercury, mercurous compounds, and mercuric compounds, while the most abundant organic form is methylmercury. Owing to its ability to permeate membranes and accumulate in organisms, methylmercury is more toxic than ionic mercury. Mercury‐resistant bacteria have developed a two enzyme system to convert both Hg (II) and methylmercury to the less toxic elemental mercury. The first enzyme is an organomercurial lyase (MerB) and the second enzyme is a mercuric ion reductase (MerA). MerB catalyzes the protonolysis of the carbon–mercury bond on a wide range of organomercurials, including methylmercury, resulting in a reduced carbon compound and ionic mercury. The cleavage of the carbon–mercury bond and the formation of the electrophile‐carbon bond are concerted (SE2). Structural studies demonstrated that MerB contains a unique fold and that significant conformational changes occur on binding of organomercurial substrates. On the basis of mutagenesis, structural, and computational studies, two cysteines and an aspartic acid residue in the active site are known to play key roles in the cleavage of the carbon–mercury bond.
Two‐Domain Multicopper Oxidase
Authors: Lawton Thomas J , Rosenzweig Amy C
Published: September 2010

Two‐domain multicopper oxidases (2dMCOs) couple the four‐electron reduction of dioxygen to the oxidation of a number of different substrates, including organic compounds and reduced ferricytochromes. The geometry of 2dMCO active sites is similar to that in other multicopper oxidases, but is formed by a significantly different protein architecture. This fold resembles the overall architecture of NO forming copper nitrite reductase (CuNIR). 2dMCOs are classified based on the location of their type‐1 copper centers.
3‐Ketosteroid‐9α‐Hydroxylase
Authors: Capyk Jenna K , Strynadka Natalie C , Eltis Lindsay D
Published: September 2010

KshAB is a Rieske oxygenase (RO) in the aerobic steroid degradation pathways of bacteria. It is a monooxygenase responsible for the 9α‐hydroxylation of the nucleus of 3‐keto‐4‐ene steroids bearing short side chains at C17. It is composed of two domains arranged in a head‐to‐tail fashion to form the functional trimer. The N‐terminal Rieske domain harbors a Fe2S2cluster in which the two irons are coordinated by two cysteine and two histidine residues, respectively. The larger, C‐terminal catalytic domain contains a mononuclear nonheme iron coordinated by a His‐His‐Asp facial triad. Purified KshAB fromMycobacterium tuberculosisexhibits substrate specificities for 1,4‐androstadien‐3,17‐one and dioxygen 2‐3 orders of magnitude lower than those measured for other ROs and their best substrates. In agreement with the large fused‐ring substrate, the structure of KshA incorporates an active site channel and substrate binding pocket that are longer than those observed in other ROs, and positioned in a different relative orientation within the catalytic domain. KshA also possesses a C‐terminal helix which occupies a position not observed in other RO structures and which likely stabilizes trimeric quaternary structure. Finally, KshA exhibits a minimal core catalytic domain with respect to secondary structural elements that may prove archetypical for ROs.
Toluene 4‐Monooxygenase and its Complex with Effector ProteinT4moD
Authors: Bailey Lucas J , Fox Brian G
Published: September 2010

Toluene 4‐monooxygenase (T4MO) is a multiprotein diiron enzyme complex that catalyzes the regiospecific oxidation of toluene top‐cresol. Catalytic function requires the presence of a small protein, called theeffector protein. Effector protein exerts substantial control on the diiron hydroxylase catalytic cycle through protein–protein interactions. High‐resolution crystal structures of the stoichometric hydroxylase and effector protein complex described here reveal how protein–protein interactions and reduction of the diiron center produce an active site configuration poised for reaction with O2. Further information from crystal structures of mutated isoforms of the hydroxylase and a peroxo adduct is combined with catalytic results to give a fuller picture of the geometry of the enzyme–substrate complex used for the high fidelity oxidation of hydrocarbon substrates.
Zinc TransporterYiiPfromEscherichia coli
Authors: Fu Dax
Published: September 2010

YiiP fromEscherichia colibelongs to the protein family of cation diffusion facilitator (CDF). CDFs play critical roles in metal homeostatic controls in microbes, plants, and mammals. They utilize the proton motive force to drive effluxes of transition metal ions out of the cytoplasm. Bacterial CDFs primarily contribute to metal resistance while mammalian CDFs are more involved in metal metabolism and cellular signaling. The crystal structure of YiiP reveals a Y‐shaped dimeric architecture, consisting of a transmembrane domain and a cytoplasmic domain that adopts a metallochaperone‐like fold. The molecular details of three distinct zinc coordination sites in YiiP delineate how metallochemistry is tailored to three central functions of CDFs: selective metal binding, rapid transport kinetics, and allosteric regulation of the transport activity. An integration of the structural information and existing biochemical data allows us to propose a two‐modular model for the operation of YiiP. In this model, the transmembrane domain is responsible for a stoichiometric zinc‐for‐proton exchange across the membrane barrier. The cytoplasmic domain detects the fluctuation of zinc concentrations and responds with a conformational change that is transmitted to regulate the activity of the transmembrane domain. In addition, the cytoplasmic domain may also serve as a zinc receiving module for uploading of the zinc cargo from a putative zinc‐metallochaperone.
X‐Ray Crystallography
Authors: Guss Jules Mitchell
Published: September 2010

X‐ray crystallography is the most extensively practised and widely applicable technique for determining molecular structures. These may be relatively small coordination complexes or metalloproteins with masses exceeding 1000 kda. The accuracy of the structures may range from a few thousands of Ǻngstrom for a small molecules to a few tenths of an Ǻngstrom for a protein. The major limitation of the technique is the requirement for well‐diffracting crystals.
Adsorption—Heterogeneous
Authors: László Krisztina
Published: September 2010

This article covers the principal features of adsorption from the practical point of view of heterogeneous catalysis. Adsorption on solid materials from both gas and liquid phases is considered. Classical interpretations and their limitations, as well as the latest developments in the evaluation methods are discussed.
Alkylation—Chemistry and Fundamentals
Authors: Albright Lyle F.
Published: September 2010

Alkylation of isobutane and aromatics have been performed commercially using liquid catalysts for many years to produce the following: high quality gasolines and alkyl benzenes (including ethyl benzene, cumene, and intermediates for detergents). Liquid–liquid dispersions or liquid–gas systems are used which contain protonic acids or Friedel–Crafts compounds as catalysts. The chemistry, which is always complicated, is reviewed to explain formation of the main products and by‐products. Different catalysts often result in significantly different chemistry. Fewer details are available on the following: relative kinetics of competing and simultaneous reactions plus physical phenomena affecting the overall processes. The ionic reactions generally occur at or near the interfacial areas between phases (often the catalyst and hydrocarbon phases). Mass transfer steps are often, if not always, of major importance. Recent information on the physical steps is discussed.
Alkylation—Industrial
Authors: Albright Lyle F.
Published: September 2010

Commercial processes to alkylate isobutane and aromatics are described and evaluated. Liquid catalysts are used for alkylations of isobutane to produce high quality gasolines. For this alkylation, solid catalysts have been widely investigated, but none has yet been commercialized. Liquid catalysts were once used exclusively for alkylation of aromatics to produce a variety of petrochemicals, but solid catalysts are now widely used. Methods on how to improve these various processes are recommended.
Ammonia Synthesis—Biological
Authors: Newton William E.
Published: September 2010

Dinitrogen (N2) in the earth's atmosphere cannot be metabolized directly by most organisms and, consequently, cellular nitrogen is usually obtained as an already reactive form, such as ammonia or nitrate. These sources of “fixed” nitrogen are relatively scarce and most often limit agricultural production. Because organic nitrogen is incompletely recycled and because available ammonia and nitrate are continually metabolized to N2, the biological reduction of N2occupies a pivotal position in the biogeochemical nitrogen cycle. This process, called nitrogen fixation, is performed only by prokaryotic microorganisms and catalyzed by the enzyme, nitrogenase. N2‐fixing microorganisms may be either free‐living or associated symbiotically with other microbes, plants, or infrequently animals. The most agriculturally significant are the symbiotic microorganisms that live within plant tissues. The most common nitrogenase is the molybdenum‐(Mo)based enzyme, but similar vanadium‐based and iron‐based enzymes are known plus a fourth unique system. The structure of its two component proteins and their 2:1 complex are known. Most nitrogenases catalyze the reduction of other substrates, such as C2H2and HCN, in reactions inhibited by CO. Substrate reduction involves association–dissociation cycles in which electrons (accompanied by MgATP hydrolysis) are transferred between component proteins. Each nitrogenase is genetically distinct, and its biosynthesis, maturation, and activity are regulated by the products of up to 19 genes. A fundamental understanding of the biochemical action and genetic regulation of the nitrogen‐fixation components has significant potential for improving the economy of nitrogen fixation, minimizing water pollution, and increasing global food supplies.
Carbonylation—Heterogeneous
Authors: Stepanov Alexander G.
Published: September 2010

In this article basic heterogeneous carbonylation catalysts known to date and their application for the conversion of the particular olefins, alcohols, alkanes into carboxylic acids, ketones, aldehydes etc., have been described. Two approaches for the design of heterogeneous catalysts are considered. The first one is a direct heterogenization of high efficiency homogeneous carbonylation catalysts used in the Reppe reaction. This approach is based on the three ways of heterogenization of homogeneous metal complexes: By anchoring on polymers, amorphous oxides or zeolites, and inert carbonaceous supports. These metal‐ or metal‐complex‐supported catalysts usually require alkyl halide promoters. The other approach consists of using the analogues of the liquid strong‐acid catalysts in the Koch reaction, that is, the pure solid acidic catalysts, such as acidic zeolites, heteropoly acids, acidic ion‐exchanged resins, and sulfated zirconia. Analysis of the carbonylation catalysts is given on the basis of the type of support used in the first approach, the required promotor, and the conditions for carbonylation performance (liquid phase or vapor‐phase carbonylation) in both approaches.
Catalyst Preparation—Homogeneous
Authors: Keep Ann
Published: September 2010

The preparation of homogeneous catalysts is discussed. Particular emphasis is given to the preparation of platinum group metal catalysts. The issues of whether to use a catalyst or catalyst precursor, that is a preformed orin situcatalyst, the catalyst oxidation state, ligand attachment, and ligand synthesis are discussed. In addition, patent issues and environmental issues are raised. The incorporation of cocatalysts and additives is discussed, and stability and handling issues are considered. Sometimes homogeneous catalysts are in fact used as precursors to nanoparticles or colloids. Some examples of homogeneous catalyst preparation are given; there are Ziegler catalysts for alkene hydrogenation, base metal catalysts such as bis(1,5‐cyclooctadiene) nickel(0) for the oligomerization of acetylene and the dimerization of dienes, (R,R)‐(–)‐(1,2‐cyclohexanediamino‐N,N′‐bis(3,5‐di‐t‐butylsalicylidene))manganese(III) chloride, Jacobsen's epoxidation catalyst, (2,6‐diisopropylphenylimido)(neophylidene)bis(hexafluoro‐tert‐butoxide)molybdenum(VI), and Schrock's alkene metathesis catalyst. Preparations of platinum group metal catalysts such as tris(triphenylphosphine)chlororhodium(I) (Wilkinson's catalyst) for hydrogenations, palladium tetrakis(triphenylphosphine) for carbon–carbon coupling reactions and iridium(cyclooctadiene)chloride dimer, a precursor for hydrogenations and hydrosilylations are also given.
Chiral Catalysts
Authors: Kégl Tamás , Kollár László
Published: September 2010

The application of optically active compounds is steadily increasing due to their biological importance. The most efficient way for their synthesis is catalysis, i.e., a reaction where a small amount of chiral material (catalyst) can transmit chirality to a large amount of substrate. Of the various types of chiral catalysts, the present article is dealing exclusively with those containing transition metals in liquid phase.

In the first part of the article the chiral ligands are arranged according to their donor atoms, and classified as phosphanes (mono‐ and bidentate phosphanes possessing various elements of chirality), nitrogen, and oxygen ligands, etc. This section is followed by chiral catalysts grouped systematically according to their central metal. (The discussion is restricted to those homogeneous chiral catalysts, where the chemical transformation of an achiral substrate possessing enantiotopic groups, atoms, faces, or centers into one enantiomer takes place.) While in the “ligand section,” the seminal works on the synthesis of the most widely used basic ligands and their first applications are demonstrated, in the “metal section,” the most recent applications (over the past 5 years) are discussed.
Chiral Catalysts
Authors: Kégl Tamás , Kollár László
Published: September 2010

The application of optically active compounds is steadily increasing due to their biological importance. The most efficient way for their synthesis is catalysis, that is a reaction where a small amount of chiral material (catalyst) can transmit chirality to a large amount of substrate.

Of the various types of chiral catalysts, the present article deals exclusively with those containing transition metals in the liquid phase.

In the first part of the article, the chiral ligands are arranged according to their donor atoms and are classified as phosphanes (mono‐ and bidentate phosphanes, possessing various elements of chirality), nitrogen and oxygen ligands, chiral dienes, etc. This section is followed by chiral catalysts grouped systematically according to their central metal. (The discussion is restricted to those homogeneous chiral catalysts, where the chemical transformation of an achiral substrate possessing enantiotopic groups, atoms, faces, or centers into one enantiomer takes place.) While the section dealing with ligand, the seminal works on the synthesis of the most widely used basic ligands and their first applications are also demonstrated and in the section dealing with metal mainly the recent catalytic (synthetic) applications over the past 10 years are discussed.
Copper Enzymes/Models
Authors: Park Ga Young , Lee Dong‐Heon , Karlin Kenneth D.
Published: September 2010

Copper is utilized as a catalytic metal center in a variety of enzymes involved in oxidation–reduction processes. The Cu(I) and Cu(II) oxidation states are readily accessible and interconvertible under physiological conditions via oxidants (ie, O
2
) or reducing agents such as ascorbic acid or glutathione. The important chemical transformations that these enzymes are responsible for include dioxygen processing as well as nitrogen oxide (NOx) conversions. The active site structures and catalytic mechanisms of the most well‐studied copper enzymes are described. The contributions to the understanding of enzyme function obtained from biomimetic studies using synthetic copper complexes of most relevance to the active site features have also been highlighted.
Cyclization—Homogeneous
Authors: Kaloko Joseph J. , Chaterpaul Stephen J. , Gary Teng Yu‐Han , Lin Chi‐Feng , Chien Chih‐Wei , Ojima Iwao
Published: September 2010

Development of highly efficient catalytic processes for the synthesis of natural and unnatural compounds of medicinal interest or useful as intermediates for functional materials is a central focus in modern organic synthesis. One of the most efficient approaches to such methodology developments is to apply transition‐metal catalyzed cyclization reactions for the transformations of simple starting materials into monocyclic, bicyclic, and polycyclic scaffolds that can be further elaborated into specific targets. This article concisely summarizes recent advances in the cyclizations promoted by homogeneous catalysts, including various carbocyclizations, carbonylative carbocyclizations, cyclohydrocarbonylations, intramolecular hydrosilylations, and silylformations, compiling relevant references up to late 2008. Among these catalytic cyclization processes, the carbocyclization and carbonylative carbocyclization are extremely important and useful reactions for the syntheses of a variety of carbocyclic and heterocyclic compounds. Cascade carbocyclization is a powerful method, providing a rapid access to polycyclic skeletons in one step. Cyclohydrocarbonylation is another powerful catalytic cyclization process, which finds a host of applications in organic syntheses. Intramolecular hydrosilylations and silylformations also provide unique methods for a variety of organic syntheses. Accordingly, catalytic cyclization reactions not only serve as highly useful synthetic methods in laboratories but also have high potential as future industrial processes.
Dehydrocyclization—Heterogeneous
Authors: Paál Zoltán
Published: September 2010

The formation of aromatic rings from alkanes such as hexane, heptane, octane, and so on (aromatization or dehydrocyclization) on oxide catalysts: chromia, lanthana, metals, such as platinum, palladium, and so on, and nonacidic (Na‐ or Ba‐L zeolite) supports is a “monofunctional” route, catalyzed by the active ingredient itself. A bifunctional route prevails in naphtha reforming (platforming) over Pt on acidic supports (eg, alumina). Interactions of Pt with acidic or alkaline support can be important for aromatization. The metallic function can also catalyze the formation of five‐membered ring(s): C5‐cyclization. The effect of added metallic components resulting in bimetallic catalysts (such as PtRe, PtSn, and so on) as well as the effect of nonmetallic components (Cl, S, C, H) is discussed. Aromatization requiring skeletal rearrangement (eg, of alkylpentane feeds) can also take place. Cyclic hydrocarbons may undergo ring enlargement and ring contraction. The same catalyst may promote the formation of a second ring in alkylcyclopentanes. The buildup of aromatic rings is also possible from smaller molecules (ethane, propane, butane) by dehydrocyclodimerization over bifunctional catalysts, such as ZSM 5 zeolites containing Pt, Zn, but first of all Ga (eg, in the CYCLAR process). Aromatics can be produced even from methane (Mo carbide‐ZSM‐5 or Pd‐Co catalysts).
History of Catalysis
Authors: Smith John Kenly
Published: September 2010

Catalysis has played a central role in the chemical industry from its beginning in the late eighteenth century. Today, catalytic processes are used to make gasoline, to synthesize most pharmaceuticals, chemicals, polymers, and to reduce pollution from cars and power plants. The discovery of new catalysts creates new products, such as polypropylene, or dramatically improves the manufacture of existing ones, such as gasoline. In the first decades of the nineteenth century, scientists, including Michael Faraday, investigated chemical reactions initiated by platinum. In 1836, Berzelius coined the word catalysis to generalize a growing body of experimental data. A half century later, Wilhelm Ostwald linked catalysis to chemical thermodynamics and kinetics by defining catalysts as substances that alter the velocity of chemical reactions without appearing in the end products. About the same time, many chemists were using heterogeneous catalysts to develop new processes, the most significant of which was the Haber, Bosch, and Mittasch ammonia process. The dramatic success of the chemical industry throughout most of the twentieth century in no small part derived from the discovery of new catalysts. Given the growing importance of catalysis to the chemical industry, many researchers investigated the fundamental mechanisms of catalysis. While many specific advances were made, no general theory emerged. Since the 1960s, academic research in catalysis has used increasingly sophisticated analytical techniques to explore catalytic phenomena at the atomic level. In part due to the maturity of the chemical industry, this new knowledge has not yet been converted into major new catalytic technologies.
Hydrogen Generation—Homogeneous
Authors: Gábor Laurenczy
Published: September 2010

Today industrial hydrogen production is dominated by processes based on heterogeneous catalysts, using fossil fuels as H
2
sources. However, homogeneous catalysts are becoming more popular in the generation of H
2
for hydrogen storage, delivery, and in mobile/on‐site or small volume hydrogen applications. Generally for these applications, the H
2
gas produced should be pure (eg, no CO contamination), the hydrogen generation should take place under mild conditions, and the H
2
supply unit should be small. Most notably, research into homogeneous catalysis has focused on the chemical storage/delivery systems, based on sodium borohydride, ammonia‐borane, hydrocarbons/alcohols, and formic acid. In the HCOOHCO
2
, cycle the greenhouse carbon dioxide gas is used as the hydrogen vector.

The use of solar energy in homogeneous catalytic H
2
gas production from water and from other hydrogen sources is the subject of extensive studies. A direct photochemical process converts solar energy into hydrogen much more efficiently than the two‐step electricity–water electrolysis/H
2
gas route.
Hydrogenases—Biological
Authors: Cammack Richard
Published: September 2010

Hydrogenases are enzymes that produce or consume hydrogen gas. Each type of hydrogenase contains, as a minimum, an iron atom, with CO and CN ligands which tune its redox potential and Lewis‐acidity to optimize the binding of dihydrogen. The Fe‐hydrogenase from methanogenic bacteria is the simplest hydrogenase and catalyzes a direct hydride transfer from H2to its organic substrate. All other hydrogenases catalyze reduction of electron acceptors, according to the equation H2= H++ 2e−. The hydrogen‐binding sites are of two types: the [NiFe(Se)]‐hydrogenases, which contain a dinuclear center of nickel and iron, and the [FeFe]‐hydrogenases, which contain a dinuclear iron site, the H cluster. In each case, the protein is arranged to leave a vacant position in the active site for binding H2, as well as separate channels for transfer of H2and H+to the surface. A chain of iron‐sulfur clusters provides a pathway for electrons to a binding site on the surface for electron acceptors and donors. O2and CO are inhibitors that bind to the vacant site and block access to H2; O2also causes oxidation of the metal centers and sulfur ligands. Some hydrogenases from aerobic bacteria, which are resistant to this inhibition, are of interest for applications in biofuel cells.
Kinetics of Catalyzed Reactions—Heterogeneous
Authors: Thybaut Joris W. , Marin Guy B.
Published: September 2010

The kinetics of heterogeneously catalyzed reactions are challenging many scientists in various fields. Catalysis is of utmost importance on the route to a sustainable society and, hence, a fundamental understanding of catalytic phenomena is of great importance. This contribution presents the requirements in order to adequately measure the intrinsic rates of catalytic reactions and how these rates can be assessed through proposed reaction mechanisms and corresponding kinetic models.
Metal Carbides
Authors: Lee Jae Sung
Published: September 2010

Transition metal carbides of early transition metals attracted considerable attention as catalysts because of their availability with high specific areas and surface cleanness. Their refractory properties render them resistance against attrition and sintering under reaction conditions. They are catalytically active in many reactions, particularly those involving hydrogen transfer such as hydrotreating (hydrodesulfurization, hydrodenitrogenation, and hydrodeoxygenation), hydrogenation, dehydrogenation, isomerization, hydrogenolysis, reforming, and aromatization. Recently, they are also receiving attention as electrocatalysis. In many of these reactions, metal carbides behave like group 8–10 metals (Pt, Pd, Rh, Ru, etc) of high cost and limited supply and have potential to replace them. Structure, bonding, synthesis, and surface reactivity of transition metal carbides are discussed.
Metal Nitrides
Authors: Lee Jae Sung , Ham Dong Jin
Published: September 2010

Transition metal nitrides are characterized by high melting points, hardness, and resistance to corrosion. These physical properties are desired for catalytic materials that require resistance against attrition and sintering under reaction conditions. Since high specific area materials became available with clean surfaces, they have attracted considerable attention as catalysts or electrocatalysts for many reactions including hydrotreating (hydrodesulfurization, hydrodenitrogenation, and hydrodeoxygenation) hydrogenation, dehydrogenation, ammonia synthesis, and fuel cell reactions. Metal nitrides demonstrate catalytic advantages over their parent metals in activity, selectivity, and resistance to poisoning. They have been found to be good catalysts for a number of reactions typically catalyzed by noble metals of high cost and limited supply. Structure, bonding, synthesis, surface reactivity, and catalysis of transition metal nitrides are discussed.
Metal Sulfides
Authors: Torres B. , Berhault G. , Chianelli R. R.
Published: September 2010

Transition metal sulfide catalysts are widely used in hydrotreatment applications particularly for removing heteroelements (S, N, O) from petroleum feedstock. The present chapter will provide description of the different catalytically active sulfides, particularly for the MoS
2
‐based catalysts promoted by Co or Ni. The different hypotheses at the origin of promotion will be first presented followed by the general procedures available for the synthesis of metal sulfides. Emphasis will also be applied to the real nature of the active phase under hydrotreating steady‐state conditions. Finally, the most recent studies based on surface science or theoretical studies will be presented.
Methane Conversion—Homogeneous
Authors: Sakakura Toshiyasu
Published: September 2010

This review article summarizes recent progress in utilization of methane as a sustainable carbon resource by homogeneous catalysis. Such conversion is a very difficult subject because the CH bond of methane is too strong to break under moderate conditions where catalyst molecules and common organic solvents can survive, and the concentration of methane in solution is usually too low. Three major synthetic targets are methanol, acetic acid, and acetaldehyde. As for the conversion of methane to methanol, the products are in many cases esters [CH3OC(O)CF3or CH3OSO3H] since it is a smart way to prevent secondary reactions of the products. Acetic acid can be formed via oxidative carbonylation or a seemingly direct addition of CO2. Methane conversions proceed through (1) electrophilic CH bond activation in a strongly acidic medium, (2) radical reactions promoted in many cases by K2S2O8, and (3) CH oxidative additions to low valent transition metal complexes. Related reactions of other hydrocarbons are also described to some extent for reference.
Nickel Enzymes/Models
Authors: Zambelli Barbara , Ciurli Stefano
Published: September 2010

The biochemical properties of the metal ions in a series of nickel enzymes are briefly reviewed. In particular, the properties of urease, hydrogenase, acetyl‐CoA synthase/carbon monoxide dehydrogenase, methyl coenzyme‐M reductase, superoxide dismutase, and acireductone dioxygenase are discussed in terms of relationships between the structure of the Ni ions in the active site and the molecular mechanism of catalysis.
Nitrogen Oxides Removal – Industrial
Authors: Forzatti Pio , Lietti Luca , Tronconi Enrico
Published: September 2010

The heterogeneous selective catalytic reduction (SCR) of NO

x

by NH
3
from stationary sources is addressed in this review. The typical commercial De‐NO

x

SCR catalysts are presented, along with their performances in both the NO

x

reduction and the SO
2
oxidation reactions. Mechanistic and kinetic aspects of the reactions involved in the SCR process, the reactor and process configurations, and the design and modeling of the SCR systems are also illustrated.
Nitrogen Oxides Removal—Industrial
Authors: Forzatti Pio , Lietti Luca , Tronconi Enrico
Published: September 2010

The trend towards more severe emission regulations has motivated in the last decades scientific and technical efforts in the removal of NOx from flue gases of stationary sources. This review surveys the present status and recent advances in the Selective Catalytic Reduction (SCR) of NOx by NH3 in stationary applications, but also includes the most recent developments on the key‐issues of the dynamics of the reaction, which are relevant for nonstationary (mobile) applications as well. Catalytic, mechanistic, kinetic, reactor and process aspects of the SCR reaction are illustrated. An account is also given of the SCONOx process, that has been recently proposed as the lowest achievable emission rate (LAER) technology for NOx removal in stationary applications.
Phase Transfer Catalysis
Authors: Mąkosza Mieczysław , Fedoryński Michał
Published: September 2010

Basic concept of phase transfer catalysis (PTC), specific features of this general methodology for executing organic reactions, and mechanism of catalytic action of PT catalysts are presented. Scope and limitations of application of PTC as a general tool of organic synthesis and advantages offered by this methodology are discussed. These discussions are illustrated by numerous examples of successful use of PTC in a variety of reactions of inorganic anions (substitution and addition reactions, β‐eliminations, oxidations, and reductions), heteroanions, and particularly carbanions (reactions with alkylating agents, carbonyl groups, activated carbon‐carbon multiple bonds, electrophilic arenes, heteroatom electrophiles) and carbenes. Possibility of use of PTC for reactions of metalloorganic compounds and complexes and for enantioselective reactions is discussed.
Synthesis Gas Generation: Industrial
Authors: van den Oosterkamp P. F.
Published: September 2010

Synthesis gas
or in short
syngas
is the term used for
mixtures of hydrogen and carbon monoxide
. Synthesis gas is an important building block for a number of petrochemicals as well as an important feedstock for liquid fuels.

The catalytic production of synthesis gas involves a number of chemical equilibrium reactions that can take place simultaneously, including undesired carbon‐forming reactions which may occur under unfavorable reaction kinetics, process conditions, or reactor design. The composition of the synthesis gas produced is determined by the thermodynamics of these quilibrium reactions.

The catalytic industrial processes for synthesis gas generation include hydrocarbon steam reforming (HSR), auto thermal reforming (ATR) and various combinations of HSR and ATR, indicated as combined reforming. The noncatalytic routes for synthesis gas generation include partial oxidation (Pox) and gasification. The drive for more fuel efficient process routes for synthesis gas production has resulted in a number of concepts for heat exchange reforming (HER) which aim to utilize the available waste heat to the maximum extent.

The main engineering issues for synthesis gas generation are related to the reactor design. For HSR, the reactor tubes are placed in a furnace, which supplies the required heat flux for the endothermic steam‐reforming reactions.

For ATR, the heat of reaction is produced in the reactor feed gas through the reaction with oxygen. For ATR, burner design is the key engineering issue.

For these high temperature reactors, selection of materials of the reactor with the correct creep rupture strength and oxidation/ carburization resistance is of paramount importance from both economical and safety point of view.

New developments in synthesis gas generation include the use of new catalytic materials, such as in the process of catalytic partial oxidation (CPO) and the use of selective membranes, which may be used to remove one of the products, for example hydrogen which may allow to shift the equilibrium reaction and performing the same conversion at a lower temperature. For all syngas production processes there is a strong integration of the catalytic materials and its associated kinetics, reactor design, and heat management at high temperatures.
Synthesis Gas Generation—Industrial
Authors: van den Oosterkamp P. F. , van den Brink R. W.
Published: September 2010

Synthesis gas or shortly syngas is a term used for a mixture of hydrogen and carbon monoxide. Synthesis gas is an important building block for a number of petrochemicals as well as an important feedstock for liquid fuels via the Fischer Tropsch route or as reducing gas for iron ore reduction.
Vanadium Enzymes/Models
Authors: Rehder Dieter
Published: September 2010

Vanadium is present in the active center of two enzyme families, viz vanadate‐dependent haloperoxidases (VHPOs) and vanadium nitrogenases (VNases). Reports on a third enzyme family, vanadium‐dependent nitrate‐reductases, await confirmation. The VHPOs, which are found in marine macro‐algae (bromoperoxidases) and in terrestrial fungi and lichen (chloroperoxidases), also exhibit sulfoxigenation and epoxidation activity. These enzymes contain vanadate H2VO4−covalently bound to a histidine in the active center. Oxidovanadium complexes with vanadium in a pentacoordinate VO(O3N) array model the VHPOs and have been employed as homogeneous or heterogeneous catalysts in (enantioselective) oxidation and oxygenation reactions, such as oxidative bromination, bromocyclization, epoxidation, sulfoxigenation, and oxygenation of unsaturated compounds. Certain vanadate‐inhibited phosphatases also exhibit haloperoxidase activity. VNases are encoded, along with the molybdenum analogs, in free‐living bacteria (Azotobacter) and cyanobacteria (Anabaena). Here, vanadium is constituent of a dicuboidal cluster (theMcluster) of core composition {VFe7S9}. Along with N2, which is reduced to N2H4and further to NH4+, protons, alkynes, and isonitriles can be substrates. The activation of N2and the reduction of substrates are modeled by low‐valent vanadium complexes.
Green Catalysis
Authors: Kaneda Kiyotomi , Mizugaki Tomoo , Mitsudome Takato
Published: September 2010

This article is an introduction to catalysis for green sustainable chemistry emphasizing typical examples of important catalytic processes. Green catalysis is discussed in relation to heterogeneous catalyses that mainly target solid acid and base catalyses for the synthesis of fine chemicals.
Recent Advances in Development, Validation, and Exploitation ofQSARModels
Authors: Tropsha Alexander
Published: September 2010

Counting more than 45 years of intensive development and applications, QSAR modeling remains one of the major computational approaches for drug discovery and environmental chemical risk assessment. Recent developments in the field reflect the burgeoning growth of bioactivity and chemical databases. This growth provides a never‐ending impetus for the development of a growing body of QSAR models and their application for virtual screening to prioritize chemicals for experimental investigations. This chapter reviews recent and emerging trends in the QSAR modeling field with the emphasis on new approaches to chemical and biological data curation, model validation, virtual screening, and potential application of QSAR models by federal agencies for regulatory decision making.