Ordered Mesoporous Pd/Silica−Carbon as a Highly Active Heterogeneous Catalyst for Coupling Reaction of Chlorobenzene in Aqueous Media

Abstract

Heterogeneous palladium catalysts, which are supported on ordered mesoporous silica-carbon nanocomposites, have been applied in water-mediated coupling reactions of chlorobenzene without assistance of any phase-transfer catalysts. Characterization by XRD, TEM, N(2) sorption, FT-IR, TG, XPS, and H(2) chemisorption techniques reveals the highly ordered mesostructure, high surface areas (approximately 345 m(2)/g), large pore volumes (approximately 0.46 cm(3)/g), uniform mesopore sizes (approximately 6.3 nm), hybrid silicate and carbonaceous compositions, and a high dispersion of palladium nanoparticles (about 3 nm) in the mesopores. The catalyst exhibits a high yield for trans-stilbene (approximately 60%) in the Heck coupling reaction of chlorobenzene and styrene at 100 degrees C and for biphenyl (46%) in the Ullmann coupling reaction of chlorobenzene at 30 degrees C, using water as a solvent. When substituted aryl chlorides (hydroxyl, methoxyl, and methyl) are involved in the Ullmann reaction, the yields of symmetrical substituted biphenyl are also higher than 44% (this value reaches 86% for the coupling reaction of 4-chlorophenol) at a low temperature of 30 degrees C. This heterogeneous catalyst is stable, which shows negligible metal leaching, and can be reused more than 20 times. For comparison, the catalytic activities for Pd catalysts supported on pure mesoporous polymeric, carbonaceous, and silicate frameworks are also investigated. The results clearly indicate that the pore wall nature shows great influence on the dispersion of metallic Pd species and, in turn, the catalytic performance.

Synthesis, characterization, and catalytic application of highly ordered mesoporous alumina-carbon nanocomposites

“…It is therefore reasonable to conclude that the appropriate Pt particle size on the OMCA nanocomposite support, controlled by the medium-strength metal-support interaction, is responsible for the superior performance of the Pt/OMCA. Very recently, Wan et al [33] reported that an ordered mesoporous carbon-silica nanocomposite exhibited a superior activity for the coupling reaction of chlorobenzene in aqueous media when Pd was supported on it. They also suggested that the nanocomposite improved the catalytic activity of Pd by affecting the Pd particle size, in agreement with our conclusion.…”

Synthesis of Partially Graphitic Ordered Mesoporous Carbons with High Surface Areas

“…[ 48 ] At the same time, the silica particles can separate carbon particles in the mesoporous composite, which may offer immobilization sites for ferric oxides and inhibit in situ reduction to metallic Fe by the organic matrix at higher temperatures. [ 49 ] Ferric oxides are the main product in the C-Fe 2 O 3 -SiO 2 composite after carbonization at 900 ° C even with a high metal content (about 3 wt.%). As a result, a high graphitic degree for GMC-2.3-900 and GMC-3-900 can be obtained by the ferric oxide catalyst and silica additive.…”

Fabrication and Characterization of Inorganic Silver and Palladium Nanostructures within Hexagonal Cylindrical Channels of Mesoporous Carbon

“…Mesoporous carbons have many potential applications both industrially and scientifically-for example, in adsorption [31][32][33][34], separation [32,34], solar cells [35], and electrodes [36]. One of the important applications of mesoporous carbons is their use as matrices for the preparation of nanometal/mesoporous carbon composites [37][38][39][40][41], similar to mesoporous carbons; there has also been some research into the preparation of various nanometal/mesoporous carbon composites for applications in catalysis [42,43] and adsorption [33].…”