**10.7. Catalysts**

des, mercury ionizes to produce the radiation having the primary wavelengths of 185 nm and 254 nm. This ultraviolet radiation, in turn, excites phosphors on the inside surface of the envelope to produce visible light that is emitted through the glass. Generally, the fluorescent lamp for illumination uses a phosphor that absorbs the 254 nm Hg-resonance wave; the phosphor is activated so as to convert the ultraviolet light into the visible light. In order to improve the color-rendering properties and the emission output of fluorescent lamps, efficient illumination of a white color has been recently provided using a three-band-type fluorescent lamp, which employs a mixture ofred, green and blue-emitting phosphors. In such three-bandtype phosphorlamp, the emitting colors of the respective phosphors are considerably different from one another. Therefore, if the emitting intensity of any of the three corresponding phosphors is decreased, the color deviation occurs, degrading the color-rendering properties of the lamp [90]. The literature dedicated to the preparation of apatite-type light-emitting

474 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

A series of orange-red-emitting Ba2Y3(SiO4)3F:xSm3+ (0.003 ≤ *x* ≤ 0.08) fluorosilicate apatite phosphors were synthesized via the conventional solid-state reaction by YU et al [91]. The emission spectra of the Ba2Y3(SiO4)3F:Sm3+ phosphors contained some sharp emission peaks of Sm3+ ions centered at 564, 601, 648 and 710 nm. The strongest one is located at 601 nm. The optimum dopant concentration of Sm3+ ions in Ba2Y3(SiO4)3F:xSm3+ is around 3 mol.% and the critical transfer distance of Sm3+ was calculated to be 26 Å. The quenching temperature is

Red-emitting phosphors Ba2Gd8(SiO4)6O2:Eu3+ (BGS:Eu3+) with silicate apatite structure were prepared by LIU et al [92] via the conventional high-temperature solid-state reaction method. There are two different sites (4*f* and 6*h* [93]) for Eu3+ occupying the host. It was found that the phosphors BGS:Eu3+ exhibit red emission with high quenching concentration at ~70.75 at.%, and the critical transfer distance of Eu3+ in BGS:Eu3+ was calculated to be ~12.3 Å. More importantly, it has better CIE chromaticity coordinate for white light-emitting diode (w-LED) application in comparison with commercial phosphor (Y,Gd)BO3:Eu3+ (YGB:Eu3+) under nearultraviolet (n-UV) 393 nm excitation [92],[94]. White Tb3+/Sm3+ ions co-doped Ca2La8(GeO4)6O2 (CLGO) phosphors prepared by JEON et al [95] show observable emission spectra under 374

A novel blue-emitting phosphor Sr8La2(PO4)6O2:Eu2+ was synthesized by LIU et al [96] via conventional high-temperature solid-state method and its photoluminescence (PL) proper‐ ties were investigated for the applications in white light-emitting diodes. The phosphor exhibited strong broad absorption band in the near-ultraviolet (n-UV) range and generated bright-blue emission centered at 442 nm upon 365 nm excitation light. The critical Eu2+ quenching concentration (QC) mechanism was verified to be the dipole-dipole interaction.

A green-emitting phosphor of Eu2+-doped Ca5(PO4)2SiO4 was prepared via a solid-state reaction by ROH et al [97]. The phosphor was excited at the wavelengths of 220 – 450 nm, which was suitable for the emission band of near-ultraviolet (n-UV) light-emitting diode (LED) (350 – 430 nm). In Ca5(PO4)2SiO4:Eu2+ phosphor, there were three distinguishable Eu2+ sites, which resulted in a strong green emission peaking at 530 nm and broad bands up to 700 nm.

phosphors is really abundant.

above 500 K.

nm excitation.

Catalysts are usually defined as the substances that increase the rate at which a chemical reaction approaches the equilibrium without becoming permanently involved in this reac‐ tion. Basically, the catalysis can be divided to [98]:


Heterogeneously catalyzed process is more complex because the catalyst is not uniformly distributed throughout the reaction medium. Considering a two-phase system, either vapor/ solid or liquid/solid, with the catalyst in the solid phase, the several steps need to be realized to complete the catalytic cycle [98]:


Due to their versatility in anionic and cationic composition and their ability to adsorb organ‐ ic and organometallic molecules as well as metallic salts, the surface properties of apatites can be tuned and they can behave as powerful catalysts in a wide range of organic reactions. In many cases, the apatite-based catalysts can be used without a solvent and show good recy‐ cling capacity. The catalytic properties mainly arise from the acid-base character of the apa‐ tite's surface. In some cases, adsorbed moieties are responsible for the catalytic properties, apatites playing the role of a solid support. Finally, the catalytic activities can result from the combination of properties of the apatite's surface and of the adsorbed or anchored moieties [99].

The oxidative Glaser-Hay coupling reaction of terminal alkynes is a very important reaction in organic chemistry to achieve the synthesis of diyne compounds. In general, the reaction is performed under homogeneous conditions using Cu(I) or Cu(II) salts in the presence of a reagent such as tetramethylethylenediamine (TMEDA), which can bind to copper ions, an organic base and dioxygen. Although this reaction is known for a long time, the mechanism is still under the discussion. It is possible to catalyze the Glaser-Hay reaction under hetero‐ geneous conditions using Cu-modified hydroxyapatite (Cu-HAp). With several para-substi‐ tuted phenyl-acetylenes and alkynols, we can show that Cu-HAp acts as a catalyst for singlebond coupling reactions leading to diyne derivatives in high yields without using auxiliary chelating molecules and organic bases. These heterogeneous conditions allow easy recovery of the catalyst and simplify the purification work-up.

The oxidative Glaser-Hay coupling reaction of terminal alkynes (acetylenes) is a very impor‐ tant reaction in organic chemistry to achieve the synthesis of diyne compounds. In general, the reaction is performed under homogeneous conditions using Cu(I) or Cu(II) salts in the presence of base (ethanolic ammonia solution, tetramethylethylenediamine, pyridine, …), which can bind to copper ions, an organic base and dioxygen [100],[101]:

$$\text{R}-\text{C}\equiv\text{CH}\xrightarrow[\text{base}]{\text{CuCl}}\text{R}-\text{C}\equiv\text{C}-\text{C}\equiv-\text{R}\tag{12}$$

Although this reaction is known for a long time, the mechanism is still under the discussion. It is possible to catalyze the Glaser-Hay reaction under heterogeneous conditions using Cumodified hydroxyapatite (Cu-HAp). With several para-substituted phenyl-acetylenes and alkynols, where Cu-HAp acts as a catalyst for single-bond coupling reactions leading to diyne derivatives in high yields without using auxiliary chelating molecules and organic bases. These heterogeneous conditions allow easy recovery of the catalyst and simplify the purification work-up [100].

The apatite catalyst was utilized for the catalysis of the synthesis of n-butanol, 1,3-butadiene and high octane fuel from bioethanol. The process requires relatively low temperature. The synthesis shows significantly lower cost compared to n-butanol derived from petroleum-based processes. The technology offers a closed-loop system with no waste or emissions [102].
