Heterogeneous catalysis at line defects I. Active sites in periodic adlayers

1972 ◽  
Vol 331 (1585) ◽  
pp. 185-193 ◽  
Keyword(s):  
Heterogeneous Catalysis ◽  
Active Sites ◽  
Linear Structures ◽  
Phase Boundaries ◽  
Enhanced Activity ◽  
Adsorbent Surface ◽  
Domain Boundaries ◽  
Structure Phase ◽  
Adsorbed Layers ◽  
Line Defects

Junctions of domain boundaries, in adsorbed layers that are otherwise periodic, are correlated with enhanced activity in heterogeneous catalysis. Such defects do not require a faulted adsorbent surface. The following linear structures can act as chains of active sites: the edges of adsorbate patches on incompletely covered adsorbent; junctions of out-of-step or rotated domains of similar structure; phase boundaries; steps; the intersections of inclined facets. The occurrence of these domain boundaries depends considerably on the symmetry and structure of both adlayer and adsorbent.

Heterogeneous catalysis at line defects II. Simple reactions

1972 ◽  
Vol 331 (1585) ◽  
pp. 195-202
Keyword(s):  
Steady State ◽  
Heterogeneous Catalysis ◽  
Catalytic Mechanism ◽  
Simple Boundary ◽  
Domain Boundaries ◽  
Adsorbed Layers ◽  
Line Defects

The ability of domain boundaries in adsorbed layers to act as effective catalysts is described. Some simple boundary-controlled reactions are analysed. Steady-state catalysis is discussed briefly in the context of catalytic mechanism.

Surface properties and adsorption characteristics to methylene blue and iodine of adsorbents from sludge

2010 ◽  
Vol 62 (8) ◽  
pp. 1705-1712 ◽  
Author(s):  
L. Y. Deng ◽  
G. R. Xu ◽  
G. B. Li
Keyword(s):  
Methylene Blue ◽  
Electrostatic Interactions ◽  
Active Sites ◽  
Pyrolysis Temperature ◽  
Weight Ratio ◽  
Surface Characteristics ◽  
Wastewater Sludge ◽  
X Ray ◽  
Adsorption Characteristics ◽  
Adsorbent Surface

Adsorbent materials created from wastewater sludge have unique surface characteristics and could be effective in adsorption applications. In this research, the sludge-adsorbents were generated by pyrolyzing mixtures of sewage sludge and H2SO4. Scanning electron microscope (SEM), thermal analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) were used to analyze the properties of sludge-adsorbent. XPS results show that the adsorbent surface functional groups with high contents of oxygen-containing groups serve as active sites for the adsorption and affect the surface characteristics; the adsorption mechanism of methylene blue (MB) is mainly Brönsted acid-base reaction between the adsorbent surface and MB; and iodine atoms are bonded to the surface of the adsorbent mainly by dispersive interactions rather than by electrostatic interactions. The results also show that H2SO4 level, pyrolysis temperature and sulfuric acid/sludge weight ratio actually affected the adsorption characteristics. Using the conditions (H2SO4 level of 1–18 M, pyrolysis temperature of 650°C, and weight ratio of 0.8), the adsorption capacities for MB and iodine were 74.7–62.3 mg g−1 and 169.5–209.3 mg g−1, respectively.

Microstructral Investigations on GaN Films Grown by Laser Induced Molecular Beam Epitaxy

1999 ◽  
Vol 595 ◽  
Author(s):  
H. Zhou ◽  
F. Phillipp ◽  
M. Gross ◽  
H. Schröder
Keyword(s):  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
Threading Dislocations ◽  
Planar Defects ◽  
Sapphire Substrates ◽  
Inversion Domain ◽  
Transmission Electron ◽  
Domain Boundaries ◽  
Line Defects ◽  
Inversion Domain Boundaries

AbstractMicrostructural investigations on GaN films grown on SiC and sapphire substrates by laser induced molecular beam epitaxy have been performed. Threading dislocations with Burgers vectors of 1/3<1120>, 1/3<1123> and [0001] are typical line defects, predominantly the first type of dislocations. Their densities are typically 1.5×1010 cm−2 and 4×109 cm−2 on SiC and sapphire, respectively. Additionally, planar defects characterized as inversion domain boundaries lying on {1100} planes have been observed in GaN/sapphire samples with an inversion domain density of 4×109 cm−2. The inversion domains are of Ga-polarity with respect to the N-polarity of the adjacent matrix. However, GaN layers grown on SiC show Ga-polarity. Possible reasons for the different morphologies and structures of the films grown on different substrates are discussed. Based on an analysis of displacement fringes of inversion domains, an atomic model of the IDB-II with Ga-N bonds across the boundary was deduced. High resolution transmission electron microscopy (HRTEM) observations and the corresponding simulations confirmed the IDB-II structure determined by the analysis of displacement fringes.

Active Sites for Heterogeneous Catalysis

1972 ◽  
Vol 43 (4) ◽  
pp. 1508-1514 ◽  
Author(s):  
Helen E. Grenga ◽  
Kenneth R. Lawless
Keyword(s):  
Heterogeneous Catalysis ◽  
Active Sites

scholarly journals Designing Heterogeneous Catalysts for Renewable Catalysis Applications Using Metal Oxide Deposition

2019 ◽  
Vol 73 (9) ◽  
pp. 698-706
Author(s):  
Yuan-Peng Du ◽  
Jeremy S. Luterbacher
Keyword(s):  
Heterogeneous Catalysis ◽  
Metal Oxide ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
High Surface ◽  
Catalyst Stability ◽  
Synthetic Control ◽  
High Oxygen Content ◽  
Oxide Deposition

Heterogeneous catalysis has long been a workhorse for the chemical industry and will likely play a key role in the emerging area of renewable chemistry. However, renewable molecule streams pose unique challenges for heterogeneous catalysis due to their high oxygen content, frequent low volatility and the near constant presence of water. These constraints can often lead to the need for catalyst operation in harsh liquid phase conditions, which has compounded traditional catalyst deactivation issues. Oxygenated molecules are also frequently more reactive than petroleum-derived molecules, which creates a need for highly selective catalysts. Synthetic control over the nanostructured environment of catalytic active sites could facilitate the creation of both more stable and selective catalysts. In this review, we discuss the use of metal oxide deposition as an emerging strategy that can be used to synthesize and/or modify heterogeneous catalysts to introduce tailored nanostructures. Several important applications are reviewed, including the synthesis of high surface area mesoporous metal oxides, the enhancement of catalyst stability, and the improvement of catalyst selectivity.

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