Catalytic Performance Of Ag Research Articles

Controlled Synthesis and Catalytic Performance of Ag3PO4 Polyhedra Photocatalysts

Ag3PO4 is an effective green photocatalyst that exhibits higher visible light photocatalytic performance for the degradation of various organic pollutants. The photocatalytic performance of Ag3PO4 is affected by the exposed high‐energy crystal facets. Herein, Ag3PO4 with different morphologies and specific surfaces is synthesized via a direct precipitation method in the presence of triethanolamine (TEA). The Ag(TEA)n complex, which served as an intermediate medium, plays a critical role during the morphological transformation. When the molar ratio of Ag+ to TEA is set as 1:12, 18‐facet polyhedral morphology of Ag3PO4 crystals is obtained. The spherical and dodecahedral samples are also obtained by adjusting the molar ratio of Ag+ to TEA as 1:1 and 1:14. The photocatalytic activity of the samples for the degradation of methylene blue (MB) is tested under visible light irradiation. It is demonstrated when the molar ratio of Ag+/TEA is 1:12, Ag3PO4 polyhedra with 18‐facet are fabricated. X‐ray diffraction and scanning electron microscopy results indicate that the 18‐facet polyhedron, with six {100} facets and twelve {110} facets, enjoys the most exposed high‐energy crystal facets. Photocatalytic experiments show that the 18‐facet polyhedron has the best performance, and the degradation of MB by Ag3PO4 polyhedron with 18‐facet morphology reaches 90% within 70 min.

An efficient Ag/MIL-100(Fe) catalyst for photothermal conversion of CO2 at ambient temperature

The conversion of CO2 under mild condition is of great importance because these reactions involving CO2 can not only produce value-added chemicals from abundant and inexpensive CO2 feedstock but also close the carbon cycle. However, the chemical inertness of CO2 requires the development of high-performance catalysts. Herein, Ag nanoparticles/MIL-100(Fe) composites were synthesized by simple impregnation-reduction method and employed as catalysts for the photothermal carboxylation of terminal alkynes with CO2. MIL-100(Fe) could stabilize Ag nanoparticles and prevent them from aggregation during catalytic process. Taking the advantages of photothermal effects and catalytic activities of both Ag nanoparticles and MIL-100(Fe), various aromatic alkynes could be converted to corresponding carboxylic acid products (86%–92% yields) with 1 atm CO2 at room temperature under visible light irradiation when using Ag nanoparticles/MIL-100(Fe) as photothermal catalysts. The catalysts also showed good recyclability with almost no loss of catalytic activity for three consecutive runs. More importantly, the catalytic performance of Ag nanoparticles/MIL-100(Fe) under visible light irradiation at room temperature was comparable to that upon heating, showing that the light source could replace conventional heating method to drive the reaction. This work provided a promising strategy of utilizing solar energy for achieving efficient CO2 conversion to value-added chemicals under mild condition.

Bio-synthesis and structural characterization of highly stable silver nanoparticles decorated on a sustainable bio-composite for catalytic reduction of nitroarenes

Bio-polymers are the most significant natural alternative stabilizers compared to their synthetic counterparts for fabrication of noble metal nanoparticles because of their higher thermal stability, renewability, low cost, eco-friendliness, strong mechanical capacity, and biodegradability properties. Therefore, a new bio-composite (CMC-Pct-AG), which is consisted of sodium carboxymethyl cellulose, agar, and pectin natural biopolymers, was fabricated as an immobilizing agent in this study. Then, highly stable silver nanoparticles (Ag NPs@CMC-AG-Pct) were successfully decorated on the surface of designed CMC-Pct-AG without the use of any hazardous reducing agents, and their chemical structures were illuminated with Uv–Vis, FT-IR, TG/DTG, SEM, EDS, XRD, and ICP-OES analyses. Subsequently, the catalytic performance of Ag NPs@CMC-AG-Pct was studied in the reduction of various nitroarenes in the presence of NaBH4 at room temperature. These tests indicate that Ag NPs@CMC-AG-Pct is an efficient catalyst which converts nitroarenes to desired amines with good yields and short reaction times. Reproducibility of the catalyst was also investigated, and it is found that Ag NPs@CMC-AG-Pct served several times as a retrievable and reusable catalyst for catalytic reduction of nitroarenes.

Catalytic performance of Ag, Au and Ag-Au nanoparticles synthesized by lichen extract

AbstractIn the present study, the green chemistry approach for the biosynthesis of Ag, Au and Ag-Au bimetallic nanoparticles (NPs) was applied using lichen extract [Cetraria islandica(L.) Ach.]. The lichen extract acts both as a reducing and stabilizing agent. The monometallic and bimetallic NPs were characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The results showed that NPs were successfully synthesized and the prepared structures were generally spherical. The synthesized nanostructures exhibited excellent catalytic activities towards reduction of nitrophenols (4-nitrophenol; 4-NP) to aminophenols (4-aminophenol; 4-AP) with sodium borohydride (NaBH4). It was determined that bimetallic NPs exhibit more effective catalytic activity than monometallic Ag and Au nanostructures. This is the first report on 4-NP reduction with Ag, Au and Au-Ag NP catalysts prepared by lichen extract.

Structural and Catalytic Properties of Ag- and Co3O4-Impregnated Strontium Titanium Ferrite SrTi0.7Fe0.3O3−δ in Methanol Steam Reforming

The catalytic performance of Ag- and Co3O4-impregnated strontium titanium ferrite (SrTi0.7Fe0.3O3-δ, STF) has been assessed in methanol steam reforming as a test reaction and accordingly correlated with spectroscopic and structural characterization after each step of a catalytic cycle including pre-oxidation and pre-reduction. After pre-reduction in hydrogen at 400 °C, metallic silver and oxidized Co in the form of Co3O4 are present. As for catalysis, it was observed that both Ag and Co3O4 are strongly promoting the methanol chemistry with respect to pure STF already at low temperatures (230 °C for both materials). As a consequence, the selectivity towards carbon monoxide is strongly enhanced in comparison to pure STF. On Co3O4-STF, the catalytic profile is basically dominated by a temperature-dependent complex interplay between methanol steam reforming, methanol dehydrogenation and the water-gas shift equilibrium. The results also prove that despite the obvious inadequacy of H2-prereduced Ag-STF to act a...

Preparation and catalytic performance of Ag, Au, Pd or Pt nanoparticles supported on 3DOM CeO2–Al2O3 for toluene oxidation

Three-dimensionally ordered macro-/mesoporous 26.9wt% CeO2–Al2O3 (denoted as 3DOM 26.9CeO2–Al2O3)-supported noble metal nanocatalysts (xM/3DOM 26.9CeO2–Al2O3, x=0.27–0.81wt%; M=Au, Ag, Pd, and Pt) were prepared using the polymethyl methacrylate-templating and polyvinyl pyrrolidone- or polyvinyl alcohol-protected reduction methods, respectively. It is shown that the xM/3DOM 26.9CeO2–Al2O3 samples displayed a high-quality 3DOM architecture with a bimodal pore (macropore size=180–200nm and mesopore size=4–6nm) structure and a surface area of 102–108m2/g, with the noble metal nanoparticles (3–4nm in size) being highly dispersed on the 3DOM 26.9CeO2–Al2O3 surface. The 0.27Pt/3DOM 26.9CeO2–Al2O3 sample performed the best (T90%=198°C at space velocity=20,000mL/(gh)) for toluene oxidation. The addition of moisture to the feedstock induced a positive effect on catalytic activity. The apparent activation energies obtained over the xM/3DOM 26.9CeO2–Al2O3 samples were in the range of 46–100kJ/mol, with the 0.27Pt/3DOM 26.9CeO2–Al2O3 sample possessing the lowest apparent activation energy. It is concluded that the good catalytic performance of 0.27Pt/3DOM 26.9CeO2–Al2O3 was associated with its higher adsorbed oxygen species concentration, better low-temperature reducibility, and stronger interaction between Pt and 3DOM 26.9CeO2–Al2O3 as well as the unique bimodal porous structure.

Ag–Cu–BTC prepared by postsynthetic exchange as effective catalyst for selective oxidation of toluene to benzaldehyde

A mixed-node MOF catalyst Ag–Cu–BTC was prepared by postsynthetic exchange (PSE) method. It is believed that PSE method can realize isomorphous replacement of Ag ion to framework Cu ion in Cu–BTC successfully. The catalytic performance of Ag–Cu–BTC was investigated via selective oxidation of toluene to benzaldehyde by molecular oxygen in the absence of solvent and initiator. This catalyst exhibits good catalytic performance: on the premise of keeping highly selective catalysis of Cu–BTC for toluene oxidizing to benzaldehyde, the introduction of Ag (Ag content is 2.76wt.%) can promote toluene conversion from 6.5% to 12.7%.

Catalytic performance of Ag–Co/CeO2 catalyst in NO–CO and NO–CO–O2 system

A new bimetallic catalyst (Ag–Co/CeO2) was studied for simultaneously catalytic removal of NO and CO in the absence or presence of O2. CeO2 prepared by homogeneous precipitation method was optimized as supports for the active components. The addition of Ag on CeO2 greatly improved the catalytic activities in the lower temperature regions (⩽300°C), and the introduction of Co on CeO2 increased the activities at higher temperatures (⩾250°C). The bimetallic Ag–Co/CeO2 catalyst combined the advantages of the corresponding individual metal supported catalysts and showed superior activity due to the synergetic effect. The effect of support, temperature, loading amount, GHSV and oxygen on catalysis was investigated. NO and CO could be completely removed in the temperature range of 200–600°C at a very high space velocity of 120 000h−1. No deactivation was observed over 4% Ag–0.4% Co/CeO2 catalyst even after 50h test.