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

Abstract

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.

Remineralization Efficacy of Four Remineralizing Agents on Artificial Enamel Lesions: SEM-EDS Investigation

“…The stoichiometric form of hydroxyapatite is shown as Ca 10 (PO 4 ) 6 (OH) 2 , and its Ca/P ratio is 1.67 [37], similar to that of G6 (1.74 ± 0.04), which is sound, not demineralized and untreated enamel. Indeed, as a result of the demineralization process, the amount of P decreases, as also found by Aoba et al [38], thus resulting in the increase in the Ca/P ratio of G5 demineralized enamel (2.00 ± 0.07).…”

S-Alkylation of dithiocarbamates via a hydrogen borrowing reaction strategy using alcohols as alkylating agents

“…23 In this regard, hydroxyapatite, the main component of bones and teeth, has attracted significant attention due to its utility as an adsorbent, 24 an ion-exchange system, 25 and an acid-base catalyst. 26 In addition, hydroxyapatite has been found to be one of the best active heterogeneous supports capable of accommodating a variety of metal salts and metal nanoparticles. 27 The incorporation of a transition metal catalyst onto a hydroxyapatite framework has led to outstanding catalytic performances in a variety of organic transformations.…”

Editorial for the Special Issue: “Hydrothermal Synthesis of Nanoparticles”

“…Furthermore, the fine particles exhibited a 3D hierarchical self-assembly process favoured by the Si 4+ ions in aqueous media coupled with rapid kinetic reaction conditions assisted by microwave heating. Additionally, the functionality of HAp NPs as potential catalyser agents was proposed by Nakagiri et al [3]. The catalytic properties of calcium hydroxyapatite NPs were investigated as a function of the Ca/P molar ratio of the HAp.…”