Influence of Magnesia on Sintering of Transition Alumina

2006 ◽  
pp. 23-28 ◽  
Author(s):  
C. Legros ◽  
F. Herbst ◽  
C. Carry
Keyword(s):  
Transition Alumina

scholarly journals Effect of process parameters on the morphology and adsorption properties of nanocrystalline boehmite

2014 ◽  
Vol 68 (3) ◽  
pp. 357-362
Author(s):  
Zoran Obrenovic ◽  
Ljubica Nikolic ◽  
Radislav Filipovic ◽  
Marija Milanovic ◽  
Ivan Stijepovic
Keyword(s):  
Ph Value ◽  
High Surface ◽  
High Surface Area ◽  
Average Crystallite Size ◽  
Sodium Aluminate ◽  
Adsorption Properties ◽  
Transition Alumina ◽  
Aluminate Solution ◽  
Bayer Liquor ◽  
Sodium Aluminate Solution

In the last decade, exploration of transition alumina phases with good adsorption properties has attracted a great research interest from both a fundamental and a practical point of view. The transition phases of alumina are metastable polymorphs of aluminum oxide formed through the thermal dehydration of aluminum trihydroxide and aluminum oxyhydroxide. Powder X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and low-temperature nitrogen absorption studies were employed to trace the formation of the transition phases of alumina. In this work transition alumina powders were synthesized starting from sodium aluminate solution prepared from Bayer liquor. The neutralization of sodium aluminate solution was performed with the use of sulphuric acid, while glucose was added in the starting solution. In this way, the single phase nanocrystalline boehmite was obtained. As-synthesized boehmite powders have high surface area (above 360 m2/g) and the average crystallite size less than 5 nm. The results showed that the properties of the powders (structure, morphology) are strongly influenced by the initial pH value of sodium aluminate solution, as well as by the duration of neutralization step.

scholarly journals CH4-to-CH3OH on Mononuclear Cu(II) Sites Supported on Al2O3: Structure of Active Sites from Electron Paramagnetic Resonance

2021 ◽  
Author(s):  
Jordan Meyet ◽  
Anton Ashuiev ◽  
Gina Noh ◽  
Mark Newton ◽  
Daniel Klose ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Organometallic Chemistry ◽  
Active Sites ◽  
Spectroscopic Characterization ◽  
Paramagnetic Resonance ◽  
Transition Alumina ◽  
Selective Conversion ◽  
Conversion Of Methane ◽  
Electron Paramagnetic ◽  
Alumina Supports

The selective conversion of methane to methanol remains one of the holy grails of chemistry, where Cu-exchanged zeolites have been shown to selectively convert methane to methanol under stepwise conditions. Over the years, several active sites have been proposed, ranging from mono-, di- to trimeric Cu(II). Herein, we report the formation of well-dispersed monomeric Cu(II) species supported on alumina using surface organometallic chemistry and their reactivity towards the selective and stepwise conversion of methane to methanol. Extensive studies using various transition alumina supports combined with spectroscopic characterization, in particular electron paramagnetic resonance (EPR), show that the active sites are associated with specific facets, which are typically found in gamma- and eta-alumina phase, and that their EPR signature can be attributed to species having a tri-coordinated [(Al<sub>2</sub>O)Cu<sup>II</sup>O(OH)]<sup>-</sup>,T-shape geometry. Overall, the selective conversion of methane to methanol, a two-electron process, involve two of these isolated monomeric Cu(II) sites that play in concert.

scholarly journals Flower-like boehmite nanopowders obtained at low temperature from Bayer liquor

2020 ◽  
Vol 14 (2) ◽  
pp. 168-172
Author(s):  
Marija Milanovic ◽  
Zoran Obrenovic ◽  
Ivan Stijepovic ◽  
Ljubica Nikolic
Keyword(s):  
Low Temperature ◽  
Specific Surface ◽  
Surface Area ◽  
Industrial Production ◽  
Single Phase ◽  
Low Cost ◽  
High Specific Surface Area ◽  
Nanocrystalline Powders ◽  
Transition Alumina ◽  
Bayer Liquor

Boehmite nanocrystalline powders were obtained by neutralization of Bayer liquor at 70?C with addition of glucose. Temperature of the neutralization induced formation of the flower-like morphology of the nanopowders. XRD and FTIR results confirmed that the single phase boehmite is formed without any other impurities. Calcination at 500?C led to the formation of transition -alumina with the retention of the flower-like morphology. Both as-synthesised and calcined powders possessed high specific surface area with mesopores between 3-6 nm in diameter. Relatively low temperature of neutralization as well as the use of low cost and ecologically friendly glucose as a surfactant are very promising for the possible application in the industrial production of alumina nanopowders.

Intrinsic and extrinsic luminescence of nanosize transition alumina powders

2013 ◽  
Vol 56 ◽  
pp. 411-414 ◽  
Author(s):  
Marek Oja ◽  
Eduard Feldbach ◽  
Aleksei Kotlov ◽  
Hugo Mändar ◽  
Sebastian Vielhauer ◽  
...  
Keyword(s):  
Transition Alumina

Characterization of metallurgical-grade aluminas and their precursors by 27Al NMR and XRD

2007 ◽  
Vol 85 (10) ◽  
pp. 889-897 ◽  
Author(s):  
Linus M Perander ◽  
Zoran D Zujovic ◽  
Tania Groutso ◽  
Margaret M Hyland ◽  
Mark E Smith ◽  
...  
Keyword(s):  
Solid State ◽  
High Field ◽  
Structural Complexity ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Nmr Studies ◽  
Transition Alumina ◽  
Angle Spinning ◽  
Alpha Alumina

The structure of metallurgical- or smelter-grade aluminas (MGAs) is complex and poorly understood. Ultra-high-field solid-state 27Al NMR results on industrial as well as on laboratory-prepared aluminas are discussed in relation to XRD results. It is demonstrated that high-field NMR can effectively be used to quantify the proportion of the thermodynamically stable alpha-alumina phase in these materials. The results demonstrate that 27Al NMR is a vital adjunct to XRD methods to quantify the transition alumina phases that invariably dominate the MGAs. The nature of the disorder in these materials, determined by 27Al NMR, is also compared with literature data, such as XANES and EXAFS studies, on typical laboratory-prepared materials. The utility of 27Al NMR studies to provide new insight into the structural complexity of metallurgical aluminas is shown.Key words: solid-state magic-angle-spinning NMR, metallurgical-grade alumina, transition alumina, gamma-alumina, coordination number.

Phase Transformation of Transition-Alumina upon Hastened Sintering

1998 ◽  
Vol 161-163 ◽  
pp. 121-124 ◽  
Author(s):  
S.D. De la Torre ◽  
Hiroki Miyamoto ◽  
Kei Miyamoto ◽  
L. Gao ◽  
Heberto Balmori-Ramírez ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Transition Alumina

Low Shrinkage Nanoscaled Transition-Alumina Crystal Aggregates of Gibbsite

2009 ◽  
Vol 92 (9) ◽  
pp. 2089-2092 ◽  
Author(s):  
Fu-Su Yen ◽  
Pei-Ling Cheng ◽  
Hong-Yun Huang ◽  
Tien-Chun Lin
Keyword(s):  
Transition Alumina

Growth of ?-Al2O3Within a Transition Alumina Matrix

1984 ◽  
Vol 67 (5) ◽  
pp. c88-c90 ◽  
Author(s):  
Karen J. Morrissey ◽  
Karel K. Czanderna ◽  
C. B. Carter ◽  
Robert P. Merrill
Keyword(s):  
Alumina Matrix ◽  
Transition Alumina
Sign in / Sign up

Export Citation Format

Share Document