Promotion of A-Site Ag-Doped Perovskites for the Catalytic Oxidation of Soot: Synergistic Catalytic Effect of Dual Active Sites

ACS Catalysis ◽  
2021 ◽  
pp. 14224-14236
Author(s):  
Lijun He ◽  
Yan Zhang ◽  
Yuchao Zang ◽  
Caixia Liu ◽  
Weichao Wang ◽  
...  
Keyword(s):  
Catalytic Oxidation ◽  
Active Sites ◽  
Catalytic Effect ◽  
A Site

scholarly journals The RelA hydrolase domain acts as a molecular switch for (p)ppGpp synthesis

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Anurag Kumar Sinha ◽  
Kristoffer Skovbo Winther
Keyword(s):  
Active Sites ◽  
Molecular Switch ◽  
Cell Physiology ◽  
Synthetase Activity ◽  
Wild Type ◽  
Functional Studies ◽  
Loop Region ◽  
A Site ◽  
Trna Binding

AbstractBacteria synthesize guanosine tetra- and penta phosphate (commonly referred to as (p)ppGpp) in response to environmental stresses. (p)ppGpp reprograms cell physiology and is essential for stress survival, virulence and antibiotic tolerance. Proteins of the RSH superfamily (RelA/SpoT Homologues) are ubiquitously distributed and hydrolyze or synthesize (p)ppGpp. Structural studies have suggested that the shift between hydrolysis and synthesis is governed by conformational antagonism between the two active sites in RSHs. RelA proteins of γ-proteobacteria exclusively synthesize (p)ppGpp and encode an inactive pseudo-hydrolase domain. Escherichia coli RelA synthesizes (p)ppGpp in response to amino acid starvation with cognate uncharged tRNA at the ribosomal A-site, however, mechanistic details to the regulation of the enzymatic activity remain elusive. Here, we show a role of the enzymatically inactive hydrolase domain in modulating the activity of the synthetase domain of RelA. Using mutagenesis screening and functional studies, we identify a loop region (residues 114–130) in the hydrolase domain, which controls the synthetase activity. We show that a synthetase-inactive loop mutant of RelA is not affected for tRNA binding, but binds the ribosome less efficiently than wild type RelA. Our data support the model that the hydrolase domain acts as a molecular switch to regulate the synthetase activity.

scholarly journals Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co1+xFe2‐xO4 Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

ChemCatChem ◽  
2021 ◽  
Author(s):  
Tobias Falk ◽  
Eko Budiyanto ◽  
Maik Dreyer ◽  
Christin Pflieger ◽  
Daniel Waffel ◽  
...  
Keyword(s):  
Catalytic Oxidation ◽  
Active Sites ◽  
Spinel Oxides ◽  
Solid Liquid

scholarly journals Influence of Impurity Dissolution on Surface Properties and NH3-SCR Catalytic Activity of Rare Earth Concentrate

Minerals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 246
Author(s):  
Zhang ◽  
Zhu ◽  
Zhang ◽  
Li ◽  
Luo ◽  
...  
Keyword(s):  
Rare Earth ◽  
Active Sites ◽  
Catalytic Effect ◽  
Catalytic Reduction ◽  
Weak Acid ◽  
Active Components ◽  
Catalyst Sample ◽  
Nh3 Scr ◽  
O2 Concentration ◽  
Alkali Leaching

Impurity removal and modification of rare earth concentrate powder were conducted by roasting weak acid-weak alkali leaching to obtain the active components of denitrification catalysts. NH3 selective catalytic reduction catalyst samples were prepared by mixing and kneading with pseudo-γ-Al2O3 boehmite as carrier. The results showed that the Ce7O12 content in the active component samples increased and dispersed more evenly. The grain size of the samples was refined, the specific surface area increased, and the active sites exposed more. Ce coexists in the form of Ce3+ and Ce4+. Fe coexists in the form of Fe3+ and Fe2+, but Fe3+ is abundant. Some Ce, La, Nd, Pr, Fe, Mn, and other components formed solid melts during preparation, which increased the synergistic catalytic effect. The denitrification efficiency of the catalyst sample was 92.8% under the conditions of reaction temperature 400 °C, NO content was 600 ppm, NH3/NO ratio was 1.5, and O2 concentration was 4%.

Understanding A-site tuning effect on formaldehyde catalytic oxidation over La-Mn perovskite catalysts

2021 ◽  
pp. 126931
Author(s):  
Junyan Ding ◽  
Jing Liu ◽  
Yingju Yang ◽  
Liming Zhao ◽  
Yingni Yu
Keyword(s):  
Catalytic Oxidation ◽  
Perovskite Catalysts ◽  
A Site

scholarly journals Structural evidence for a proline-specific glycopeptide recognition domain in an O-glycopeptidase

Glycobiology ◽  
2020 ◽  
Author(s):  
Ilit Noach ◽  
Alisdair B Boraston
Keyword(s):  
Active Sites ◽  
Substrate Recognition ◽  
Peptide Bond ◽  
Multidomain Protein ◽  
Threonine Residue ◽  
Tyrosine Residues ◽  
Host Pathogen Interaction ◽  
A Site ◽  
Insight Into

Abstract The glycosylation of proteins is typically considered as a stabilizing modification, including resistance to proteolysis. A class of peptidases, referred to as glycopeptidases or O-glycopeptidases, circumvent the protective effect of glycans against proteolysis by accommodating the glycans in their active sites as specific features of substrate recognition. IMPa from Pseudomonas aeruginosa is such an O-glycopeptidase that cleaves the peptide bond immediately preceding a site of O-glycosylation, and through this glycoprotein-degrading function contributes to the host-pathogen interaction. IMPa, however, is a relatively large multidomain protein and how its additional domains may contribute to its function remains unknown. Here, through the determination of a crystal structure of IMPa in complex with an O-glycopeptide, we reveal that the N-terminal domain of IMPa, which is classified in Pfam as IMPa_N_2, is a proline recognition domain that also shows the properties of recognizing an O-linked glycan on the serine/threonine residue following the proline. The proline is bound in the center of a bowl formed by four functionally conserved aromatic amino acid side chains while the glycan wraps around one of the tyrosine residues in the bowl to make classic aromatic ring-carbohydrate CH-π interactions. This structural evidence provides unprecedented insight into how the ancillary domains in glycoprotein-specific peptidases can noncatalytically recognize specific glycosylated motifs that are common in mucin and mucin-like molecules.

The electronic structure and geometric structure of nanoclusters as catalytic active sites

2013 ◽  
Vol 2 (5) ◽  
pp. 515-528 ◽  
Author(s):  
Hao Li ◽  
Linsen Li ◽  
Yadong Li
Keyword(s):  
Electronic Structure ◽  
Heterogeneous Catalysis ◽  
Metal Nanoparticles ◽  
Research Methods ◽  
Geometric Structure ◽  
Active Sites ◽  
Catalytic Effect ◽  
The Past ◽  
Catalytic Active Sites ◽  
Made In

AbstractIn the past few decades, metal nanoparticles applied in heterogeneous catalysis have attracted extensive attention. The term nanocatalysis is broadly referred to as the unique catalytic effect of this series of materials. Although considerable progress has been made in nanocatalysis, it still remains a great challenge to fully understand the nature of active sites in the nanoscale. Many concepts and models have been put forwarded to describe the properties and performances of nano- and subnanoparticles in catalysis. In this review, we propose our perspective on the active sites of heterogeneous catalysis from the aspects of electronic structure and geometric structure of nanoclusters and consider briefly how these clusters function in catalysis. The challenge in nanocatalysis research methods is also discussed.

EFFECTS OF FINITE REACTION RATES ON THE KINETIC PHASE TRANSITIONS IN THE CATALYTIC OXIDATION OF CARBON MONOXIDE

2002 ◽  
Vol 09 (05n06) ◽  
pp. 1735-1739
Author(s):  
L. D. LÓPEZ-CARREÑO
Keyword(s):  
Carbon Monoxide ◽  
Phase Transitions ◽  
Steady State ◽  
Catalytic Oxidation ◽  
Active Sites ◽  
Nearest Neighbor ◽  
Reaction Rates ◽  
Neighbor Site ◽  
State Configuration ◽  
Oxidation Of Carbon Monoxide

Oxidation of carbon monoxide is one of the most extensively studied heterogeneous catalysis reactions, being important among other applications in automobile-emission control. Catalytic oxidation of carbon monoxide on platinum (111) surface was simulated by the Monte Carlo technique following an extended version of the model proposed by Ziff, Gulari and Barshad (ZGB). In the simulation, a simple square two-dimensional lattice of active sites replaces the surface of the catalyst. Finite reaction rates for (i) diffusion of the reactive species on the surface, (ii) reaction of a CO molecule with an oxygen atom in a nearest neighbor site, and (iii) desorption of unreacted CO molecules, have been taken into account. The produced CO 2 desorbs instantly. The average coverage of O, CO and the CO 2 production rate for a steady state configuration, as a function of the normalized CO partial pressure (P CO ), shows two kinetic phase transitions. In the ZGB model these transitions occur at P CO ≈ 0.39 and P CO ≈ 0.53. For 0.39 < P CO < 0.53 a reactive ( CO 2 production) steady state is found. Outside of the interval, the only steady state is a poisoned catalyst of pure CO or pure O. Our results show that finite reaction rates shift the values in which these phase transitions occur.

Strontium Ruthenate Perovskites with High Specific Capacitance for use in Electrochemical Capacitors

1997 ◽  
Vol 496 ◽  
Author(s):  
P. M. Wilde ◽  
T. J. Guther ◽  
R. Oesten ◽  
J. Garche
Keyword(s):  
Active Sites ◽  
Metal Salt ◽  
High Specific Capacitance ◽  
Amorphous Structure ◽  
Charge Balance ◽  
X Ray Diffraction ◽  
New Synthesis ◽  
Capacitive Properties ◽  
A Site ◽  
Similar Phase

ABSTRACTStrontium ruthenates with the perovskite type structure ABO3 have been shown to exhibit attractive capacitive properties. Doping on the A site with La lead to typical capacitance values of 21 F/g. These materials were synthesized by coprecipitating metal hydroxides from a stoichiometric salt solution and subsequent firing at 800 °C in air. In this paper we present a new procedure to synthesize the materials which are crystalline and nevertheless show appreciable capacitances in contrast to ruthenium dioxide material, which only works in a hydrated amorphous structure. The process basically consists in a pyrolysis of concentrated metal salt solutions of the respective chlorides and nitrates at 500 °C for several minutes. Excess soluble phases are removed by washing out with water. X-ray diffraction experiments revealed similar phase purity and crystallinity as known from the coprecipitated materials. However the measured capacitances of undoped perovskites reached high values of 200 F/g exceeding twenty times the value of respective coprecipitated materials. First experiments on doping the materials promise further progress. The new synthesis route introduces a higher surface area by leaving cavities from leached soluble phases and bulk defects into the crystal structure. The first effect increases the number of active sites in contact with the electrolyte while the latter enhances the protonie conduction which is necessary to keep the charge balance within the material during cycling.

Cooxidation reactions of ascorbic acid

1979 ◽  
Vol 44 (10) ◽  
pp. 2893-2903 ◽  
Author(s):  
Eva Schwertnerová ◽  
Dana M. Wagnerová ◽  
Josef Vepřek-Šiška
Keyword(s):  
Hydrogen Peroxide ◽  
Ascorbic Acid ◽  
Salicylic Acid ◽  
Catalytic Oxidation ◽  
Molecular Oxygen ◽  
Catalytic Effect ◽  
Metal Chelates ◽  
Dihydroxybenzoic Acid ◽  
Reaction Intermediate ◽  
Kinetics Of

Catalytic oxidation of salicylic acid by molecular oxygen, induced by the oxidation of ascorbic acid, leads to the formation of a mixture of isomers of dihydroxybenzoic acid. The reaction is catalyzed by a series of metal chelates, especially Fe(II) and Co(II), the most marked catalytic effect having been found in the case of tetrasulphophthalocyanine of cobalt (CoTSP). The kinetics of the oxidation of ascorbic acid in the presence of salicylic acid was followed, and the formation of hydrogen peroxide as reaction intermediate was proved.

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