Silica‐Supported Silver Nanoparticles with Surface Oxygen Species as a Reusable Catalyst for Alkylation of Arenes

Abstract

A series of silica‐supported silver catalysts with various Ag loading (3–30 wt %) and different treatment (oxidation and subsequent reduction by H2) were prepared, and their local structures were characterized by extended X‐ray absorption fine structure (EXAFS) analysis. In oxidized catalysts, silver were mainly present as small nanoparticles with surface oxygen atoms, and the number of surface oxygen atoms decreased with increased silver loading. The H2 reduction of these samples resulted in a removal of the surface oxygen atoms. The structure–activity relationship was studied for the alkylation of anisole with benzyl alcohol and styrene. AgI oxide, AgI ion, bulk silver metal, and silica‐supported silver nanoparticles were non‐active species. In contrast, silica‐supported silver nanoparticles with the surface oxygen atoms acted as an effective heterogeneous catalyst for the alkylation of arenes with alcohols and styrenes. Kinetic studies in alkylation of anisole with alcohols showed that the cleavage of the α‐CH bond of alcohol was the rate‐limiting step. It is proposed that the surface oxygen adjacent to the silver surface atoms plays an important role in the dissociation of the α‐CH bond.

Highly Selective Liquid-Phase Benzylation of Anisole with Solid-Acid Zeolite Catalysts

“…The conversion of benzyl alcohol was completed in 45 min irrespective of the substituents on anisole, however the distribution of ortho, meta, and para isomer products was altered (Figure 7). The obtained distribution of isomers was in close agreements with the orientation abilities of substituents on anisole [29]. Since the benzylation reaction is expected to follow an electrophilic substitution pathway (similar to Friedel-Craft reactions) the stability of the benzyl carbocation (electrophile) should play a major role in the rate of the benzylation reaction.…”

“…The yields of mono-benzylated products of anisole with the examined benzylating agents were all found to be high but following the order of: dibenzyl ether > benzyl alcohol > benzyl chloride > benzyl bromide. This order can be rationalized by the size of the leaving groups, thus supporting formation of benzyl carbocataions from reaction between the surface Brønsted acid sites of H-MOR-10 and the alkylating agent to be the rate determining step in the reaction [29]. The selectivity of benzyl alcohol and DBE to mono-alkylated products was slightly higher than for the benzyl halides, suggesting the alcohol or the ether to be the preferred alkylating agent under the given reaction conditions.…”

“…In addition, niobium oxide [8] (Nb 2 O 5 ), niobium phosphate (H 3 PO 4 -WO 3 -Nb 2 O 5 ) [11,26], phosphated and sulfated mesoporous niobium oxide [27] as well as alumina-supported niobium oxides [28] have also been reported to be active catalysts -but not very selective -for the 3 benzylation of benzene, toluene and anisole. Silver nanoparticles supported on silica are also reported as heterogeneous catalyst for the alkylation of arenes [29]. However, low yield of monobenzylated product and use of a transition metal is not attractive for practical use.…”

A novel green one-step synthesis of silver nanoparticles using chitosan: catalytic activity and antimicrobial studies

“…Silver nanoparticles are of particular interesting due to their role as substrates in the studies of catalysis (Tsujino and Matsumura 2005;Shimizu et al 2010), surface enhancement, Raman spectroscopy (Debarre et al 2004;Terekhov et al 2011) and in the biomedical field (Xu et al 2006;Liu et al 2010;Krishna Rao et al 2012). Because of their vast applications in various fields, many techniques of synthesizing silver nanoparticles have been investigated and some of them are: chemical reduction (Bhui and Misra 2012), electrochemical reduction (Starowicz et al 2006;Hosseini and Momeni 2010), photochemical reduction (Kutsenko and Granchak 2009), microemulsion (Zhang et al 2011), gamma-ray irradiation (Huang et al 2009;Rao et al 2010), UV irradiation (Spadaro et al 2010), ultrasonic method (Byeon and Kim 2012), microwave method (Nadagouda et al 2011), etc.…”

Synthesis and Characterization of Pure and Nano-Ag Impregnated Chitosan Beads and Determination of Catalytic Activities of Nano-Ag

“…The nano-Ag was preferably anchored due to its unique optical, conductive [4,5], and biomedical properties [6][7][8]. The nano-Ag can also demonstrate reliable oxidative and reductive catalytic properties [9,10].…”