scholarly journals The Role of the Surface Acid–Base Nature of Nanocrystalline Hydroxyapatite Catalysts in the 1,6-Hexanediol Conversion

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 659
Author(s):  
Asato Nakagiri ◽  
Kazuya Imamura ◽  
Kazumichi Yanagisawa ◽  
Ayumu Onda

Hydroxyapatite is known to have excellent catalytic properties for ethanol conversion and lactic acid conversion, and their properties are influenced by the elemental composition, such as Ca/P ratio and sodium content. However, few reports have been examined for the surface acid–base nature of hydroxyapatites containing sodium ions. We prepared nanocrystalline hydroxyapatite (Ca-HAP) catalysts with various Ca/P ratios and sodium contents by the hydrothermal method. The adsorption and desorption experiments using NH3 and CO2 molecules and the catalytic reactions for 2-propenol conversion revealed that the surface acid–base natures changed continuously with the bulk Ca/P ratios. Furthermore, the new catalytic properties of hydroxyapatite were exhibited for 1,6-hexanediol conversion. The non-stoichiometric Ca-HAP(1.54) catalyst with sodium ions of 2.3 wt% and a Ca/P molar ratio of 1.54 gave a high 5-hexen-1-ol yield of 68%. In contrast, the Ca-HAP(1.72) catalyst, with a Ca/P molar ratio of 1.72, gave a high cyclopentanemethanol yield of 42%. Both yields were the highest ever reported in the relevant literature. It was shown that hydroxyapatite also has excellent catalytic properties for alkanediol conversion because the surface acid–base properties can be continuously controlled by the elemental compositions, such as bulk Ca/P ratios and sodium contents.

Author(s):  
Takashi Yamamoto ◽  
Akihito Kurimoto ◽  
Riona Sato ◽  
Shoki Katada ◽  
Hirotaka Mine ◽  
...  

Ethanol conversion by Ga2O3-ZrO2 solid solution was examined in the temperature range 573–773 K, and acetone/isobutene formation was confirmed under cofeeding of H2O vapor. The reaction pathway was empirically investigated...


Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 5942
Author(s):  
Dongfei Xu ◽  
Jiaan Ren ◽  
Shengnan Yue ◽  
Xiujing Zou ◽  
Xingfu Shang ◽  
...  

A series of Al-P-O catalysts (Al-xP-O) were prepared using a P123-assisted one-pot method at different P/Al molar ratios and used for O-methylation of catechol and methanol. The influences of the P/Al molar ratio and P123 addition on catalyst structure and surface acid-base characteristics were investigated in detail. Increasing the P/Al molar ratio more favored crystalline aluminophosphate. The P123-assisted Al3+ and PO43− are known to be stabilized through weak steric force so that the formation of crystalline aluminophosphate could be inhibited at higher P/Al molar ratios. The results showed that the prepared Al-P-O catalysts possessed appropriate weak acid and weak base sites, which was beneficial to the reaction of catechol and methanol. The Al-1.1P-O catalyst synthesized with the assistance of P123 exhibited superior catalytic performances, with 52.5% catechol conversion and higher guaiacol selectivity of 97.6%.


Author(s):  
L.D. Schmidt ◽  
K. R. Krause ◽  
J. M. Schwartz ◽  
X. Chu

The evolution of microstructures of 10- to 100-Å diameter particles of Rh and Pt on SiO2 and Al2O3 following treatment in reducing, oxidizing, and reacting conditions have been characterized by TEM. We are able to transfer particles repeatedly between microscope and a reactor furnace so that the structural evolution of single particles can be examined following treatments in gases at atmospheric pressure. We are especially interested in the role of Ce additives on noble metals such as Pt and Rh. These systems are crucial in the automotive catalytic converter, and rare earths can significantly modify catalytic properties in many reactions. In particular, we are concerned with the oxidation state of Ce and its role in formation of mixed oxides with metals or with the support. For this we employ EELS in TEM, a technique uniquely suited to detect chemical shifts with ∼30Å resolution.


2021 ◽  
Vol 141 ◽  
pp. 106539
Author(s):  
Tran Ngoc ◽  
Ho Van Tuyen ◽  
Le Anh Thi ◽  
Le Xuan Hung ◽  
Nguyen Xuan Ca ◽  
...  
Keyword(s):  

Author(s):  
Pavel Mayorov ◽  
Elena Asabina ◽  
Anna Zhukova ◽  
Diana Osaulenko ◽  
Vladimir Pet’kov ◽  
...  

Symmetry ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1168
Author(s):  
Elena Belenkaya ◽  
Ivan Pensionerov

On 14 January 2008, the MESSENGER spacecraft, during its first flyby around Mercury, recorded the magnetic field structure, which was later called the “double magnetopause”. The role of sodium ions penetrating into the Hermean magnetosphere from the magnetosheath in generation of this structure has been discussed since then. The violation of the symmetry of the plasma parameters at the magnetopause is the cause of the magnetizing current generation. Here, we consider whether the change in the density of sodium ions on both sides of the Hermean magnetopause could be the cause of a wide diamagnetic current in the magnetosphere at its dawn-side boundary observed during the first MESSENGER flyby. In the present paper, we propose an analytical approach that made it possible to determine the magnetosheath Na+ density excess providing the best agreement between the calculation results and the observed magnetic field in the double magnetopause.


2013 ◽  
Vol 14 (2) ◽  
pp. 382-395 ◽  
Author(s):  
Leonardo Marmo Moreira ◽  
Fernando de Paula Leonel ◽  
Ricardo Augusto Mendonça Vieira ◽  
José Carlos Pereira

The decisive role of metallic cations in the formation of supramolecular clusters involving lignin, cellulose, and hemi-cellulose and its relationship to energy losses in ruminants associated with fibrous feed resources is still not well understood. Indeed, interactions between lignin, cellulose and metallic cations generate highly stable clusters that significantly decrease the capability of cellulase to break bonds between sugar units in order to facilitate the absorption of a great quantity of cellulose, which is ingested by ruminants as forage. Furthermore, several metallic cations cannot be absorbed as a consequence of the formation of coordinated ligations with the oxygen atoms of the lignocellulosic cluster. The loss of lignocellulose-metal clusters by ruminants is responsible for a substantial waste of nutrients, which is a significant problem in animal science. Moreover, the chemical structure of these relevant supramolecular systems is poorly understood. In the present review, we discussed this topic in detail in reference to relevant literature from the chemical and animal sciences in order to analyze the perspectives associated with the improvement of nutritional absorption from feed resources by ruminants.


2016 ◽  
Vol 242 ◽  
pp. 29-37 ◽  
Author(s):  
Abhishek Kumar Gupta ◽  
Yogendra Lal Verma ◽  
Manish Pratap Singh ◽  
Rajendra Kumar Singh
Keyword(s):  

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