Kinetic and DFT Studies on the Ag/TiO₂‐Photocatalyzed Selective Reduction of Nitrobenzene to Aniline

Abstract

TiO2 particles loaded with silver nanoparticles with a mean diameter of 1.5 nm exhibit a high photocatalytic activity (84 % conversion after 1 h irradiation) for the reduction of nitrobenzene to aniline with 100 % selectivity in the presence of CH3OH (concentration=100 mM). High-resolution transmission electron microscopic studies of Pt-photodeposited Ag/TiO2 demonstrate that the Ag nanoparticles act as reduction sites in the photocatalytic reaction. Both spectroscopic measurements and density functional theory (DFT) calculations reveal that nitrobenzene is selectively adsorbed onto the Ag surfaces of Ag/TiO2 via partial electron transfer from Ag to nitrobenzene, whereas the interaction between aniline and Ag/TiO2 is weak. The kinetic analysis indicates that the recombination between the electrons flowing into the Ag nanoparticle and the holes left in the TiO2 valence band is significantly suppressed, particularly in the presence of CH3OH. The high activity and selectivity in the present Ag/TiO2-photocatalyzed reduction are rationalized in terms of the charge separation efficiency, the selective adsorption of the reactants on the catalyst surfaces, and the restriction of the product readsorption.

Effect of acrylic acid feed contents of microgels on catalytic activity of silver nanoparticles fabricated hybrid microgels

“…For example, p-nitrophenol (p-NP), 9,18 nitrobenzene (NB), 19,20 o-nitrophenol (o-NP) 21,22 and m-nitrophenol 22 can be reduced in aqueous medium using metal nanoparticles as catalysts. Aggregation or coagulation of nanoparticles limits their activity in the field of catalysis, because catalysis is a surface phenomenon and coagulation of nanoparticles results in a decrease in surface area.…”

Surface Properties and Photocatalytic Activity of Ptcore/Agshell Nanoparticle‐Loaded TiO2

“…[18] First, oxidation (TiO 2 ) and reduction sites (Ag) are separated by the Ag, although a feature of TiO 2 photocatalysis is that oxidation and reduction concurrently proceed at adjacent sites on the surface. Second, the substrates to be reduced (NB) and oxidized (CH 3 OH and/or H 2 O) are selectively and abundantly supplied to the reduction and oxidation sites, respectively.…”

“…The structure of the Ag shell layer could not be determined directly by HRTEM; however, the (111) plane having the smallest surface energy in the fcc crystal structure tends to be exposed on the surfaces of both Pt (Figure 1 B) and Ag nanoparticles. [18] Thus, by assuming an epitaxial growth of the Ag layer on the PtA C H T U N G T R E N N U N G (111) surface, [20] one can estimate the value of n L from the division of half the increment in d after the Ag photodeposition by the AgA C H T U N G T R E N N U N G (111) lattice spacing (0.235 nm). [21] A good linear relation is obtained between the mean number of the Ag shell layer (n L ) and y for the PtAg/TiO 2 samples with varying Ag amounts, which were prepared by changing the AgNO 3 concentration during Ag photodeposition: n L = 9.23 y + 0.08 (R 2 = 0.995).…”

“…More recently, we have found that the reaction is drastically enhanced with the loading of Ag nanoparticles on less active TiO 2 . [17,18] This reaction can also be expected to provide information regarding the reduction of NO x , which is important from the perspective of environmental conservation. [19] This article reports a 2-step photochemical method for preparing Pt@Ag nanoparticle loaded-TiO 2 (Pt@Ag/TiO 2 ) with varying mean Ag shell layer number (n L ), and analysis of the surface properties of Pt@Ag/TiO 2 and its reactivity in the photocatalytic reduction of NB as a function of n L .…”

Factors affecting the selectivity of the photocatalytic conversion of nitroaromatic compounds over TiO2 to valuable nitrogen-containing organic compounds

“…The photocatalytic reduction of the nitro group to the amino group on the surface of TiO 2 , in the absence of oxygen and in the presence of alcohols as sacrificial electron donors, is well established and summarized in eqn (1)-(6). [13][14][15] ). The potential of the conduction band electrons in the anatase phase was reported 16 to be À0.908 V vs. SCE at pH = 12 which is negative enough to reduce almost all nitrobenzene derivatives (formal potentials of m-NH 2 -Ph-NO 2 , m-CH 3 -Ph-NO 2 , m-Cl-Ph-NO 2 , are, respectively, À0.705, À0.705, À0.635 V vs. SCE at pH E 12).…”