Nanozarah titanium-karbon terkurung dalam silika mesoliang sebagai mangkin untuk pengoksidaan stirena

Abstract

Nano-sized metal for heterogeneous catalytic process has attracted the attention of many researchers due to its surface area and high efficiency in the liquidliquid phase reaction. For oxidation o f organic compounds with H2O2 as the oxidant, not only nano-sized catalysts are needed, but also the presence o f organic moiety at the surface o f metal active site, besides having the silica shell. Therefore, titanium nanoparticles that have covalent bonding with organic compounds (T i-C ) and with the silica shell are expected to increase stability and activity o f the Ti-C nanoparticles (Ti-C@ SiO2). In this study, the Ti-C nanoparticle was synthesized by the reduction method with three different organic groups i.e. phenyl, phenol and thiophenol. Meanwhile, the silica shells o f the Ti-phenyl, Ti-phenol, Ti-thiophenol surfaces were synthesized via hydrolysis of TEOS. The catalysts were characterized using various techniques such as FTIR, DR-UV-Vis, TGA, NMR, XRD, FESEM, TEM, adsorption-desorption o f nitrogen analysis (BET) and pore volume analysis. The existence of silica shell with its morphology and porosity confirmed by FESEM and BET showed the agglomeration of Ti-C in the silica shell with nearly spherical shape and in mesopore size range. The titanium metals with lattice spacings o f 2 .2 A and 1.8 A in Ti-phenyl@SiO2, Ti-phenol@SiO2and Ti-thiophenol@SiO2 nano particles have sizes in the range o f 3-5 nm, 3-10 nm, and 3-10 nm, respectively. Furthermore, the Ti-phenyl, Ti-phenyl@SiO2 and commercial anatase (TiO2) were applied as catalysts for the oxidation of alkenes such as 1 -dodecene, 1 -octene, and styrene. The results show that, Ti-phenyl@SiO2 was inactive for both 1-octene and 1 -dodecene oxidation. Ti-phenyl, Ti-phenol, and Ti-thiophenol show high catalytic activity for oxidation of styrene but cannot be reused. However, the Ti-phenyl@SiO2 shows high catalytic activity for styrene oxidation and can be reused with only ca. 10% decrease in conversion. The Ti-phenyl@SiO2 with Si/Ti mol ratio of 2 exhibits the highest catalytic performance for alkene oxidation, especially for styrene with 92% o f conversion and 99% of selectivity towards benzaldehyde. In addition, the Ti-phenol@SiO2(1) was the most active among the catalysts with 90% o f conversion and 99% o f selectivity towards benzaldehyde. Meanwhile, the Ti-thiophenol@SiO2(2 ) catalyst was the most active to produce benzaldehyde with the conversion of 80% and selectivity of 97%. The high catalytic activity shown by Ti-C@ SiO2 catalysts in the oxidation of styrene can be explained based on structural similarity of the phenyl group of Ti-phenyl@SiO2 catalysts with the styrene structure, and the easier access of the substrates to the Ti active sites due to the mesoporous silica shells.