The dehydrogenation of lower alkanes was investigated on Pt–Sn/SiO2 catalysts prepared by impregnation with different thermal treatments. The treatment atmosphere played an important role in both the ...catalytic performance and the catalyst structure. An ensemble containing several adjacent Pt and Sn atoms from Pt–SnO2 or Pt–Sn alloy nanoparticles acts as the active site for dehydrogenation of lower alkanes, which can be respectively induced by treatment in an inert atmosphere (N2) or reductive atmosphere (H2) at high temperature.
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•Pt-SnO2 SMSI in Pt–Sn/SiO2 can be constructed via thermal treatments.•An ensemble containing Pt and Sn atoms acts as the active site for dehydrogenation.•The geometric effect of Sn on Pt contributes to the superior catalytic performance.
The addition of tin (Sn) is commonly used as a design strategy for catalyst optimization of platinum-based catalysts. The mechanistic understanding of this class of systems is, however, obscured by the structural complexity. Herein, a series of catalyst characterization techniques including X-ray absorption fine structure (XAFS) and in-situ CO diffuse reflectance infrared fourier transform spectroscopy (CO-DRIFTS) were utilized to study the catalyst structure. It was found that the structure and catalytic properties are closely related with the interaction between Pt and SnO2 (specifically the Pt-SnO2 strong metal-support interaction (SMSI)), which can be continuously tuned by thermal treating the Pt-Sn/SiO2 precursor at different atmospheres and temperatures. The treatment in an oxidative atmosphere (O2) also can generate Pt-SnO2 SMSI, which became weak at higher temperatures and led to the growth of Pt nanoparticles (NPs). Pt-SnO2 SMSI became stronger when the oxygen atmosphere was changed to an inert (N2) atmosphere. Small metallic Pt NPs were formed and their dispersion was increased with increasing treatment temperature with inert gas. The catalyst presented a moderate activity in the dehydrogenation of lower alkanes. The treatment in a reductive atmosphere (H2) produced the strongest Pt-SnO2 SMSI and most active catalyst. Highly dispersed Sn surface-enriched Pt–Sn alloy NPs were formed on SiO2, in which Pt was most electron rich. The apparent activation energy in n-butane dehydrogenation is higher on Pt–Sn/SiO2_1073 K H2 than the corresponding one on Pt–Sn/SiO2_1073 K N2. The kinetic studies revealed that the extreme isolation of Pt on Pt–Sn/SiO2_1073 K H2 (geometrical effects) dominantly contributed to its superior catalytic performance. The present work highlights the effects of thermal treatment-induced Pt-SnO2 SMSI, providing a new insight into the structure of Pt–Sn bimetallic catalysts and the promotional role of Sn in the dehydrogenation of lower alkanes to olefins on Pt surfaces.
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•WO3/Al2O3–TiO2 showed high activity for Brønsted acid-catalyzed reactions.•Brønsted acids were formed at the boundaries between amorphous WO3 and Al–Ti support.•Surface Lewis acid ...and OH groups are key to form Brønsted acid on Al2O3-based supports.
The effect of alumina-based supports (Al2O3, Al2O3–TiO2, Al2O3–ZrO2, SiO2–Al2O3, and SiO2) on the structure and acid properties of supported tungsten oxide catalysts was investigated. Among the tested supported tungsten oxide catalysts, WO3/Al2O3–TiO2 (Al2O3/TiO2 = 9, Al–Ti9) showed the highest activity for reactions catalyzed by Brønsted acid sites and the largest Brønsted acidity. Structural characterization revealed that Brønsted acid sites on WO3/Al–Ti9 were generated at the boundaries between domains of amorphous monolayer WO3 and Al2O3–TiO2 support and WO3/Al2O3 reported previously, and that Al2O3 and Al–Ti9 with a high density of Lewis acid and surface hydroxyl groups resulted in the formation of Brønsted acid sites. Crystalline WO3 species formed mainly on SiO2–Al2O3 and SiO2 with a low density of Lewis acid sites and a high density of surface hydroxyl groups. These results suggested that a high density of Lewis acid sites and surface hydroxyl groups are important factors to form amorphous WO3 monolayer domains and to generate Brønsted acid sites on alumina-based supports.
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•The selective catalytic oxidation of NH3 (NH3-SCO) at low temperatures was studied.•Mordenite-supported Pt-Au alloy catalysts with various Pt:Au ratios were prepared.•The NH3 ...conversion and N2 selectivity depended on the Pt:Au ratio.•The effect of combination of electron-deficient Pt and electron-rich Au was investigated.•Brønsted acid sites were found to be essential for the selective formation of N2.
The selective catalytic oxidation of ammonia (NH3-SCO) to N2 and H2O at low temperatures was studied to remove low-concentration (50 ppm) NH3 from the air. A series of mordenite (M20)-supported Pt-Au alloy catalysts with different Pt:Au ratios were synthesized and tested in the NH3-SCO. The NH3 conversion and N2 selectivity both depended on the ratio of Pt to Au. The 0.52 wt% Pt84Au16/M20 catalyst showed the highest NH3 conversion (90% at 144 °C) even better than Pt100/M20, which was ascribed to the combination of electron-deficient Pt and electron-rich Au in the alloy nanoparticles. The effects of acid sites on the NH3-SCO were investigated by NaOH treatment of Pt84Au16/M20 catalyst. Results suggested that the acid sites could help to increase NH3 conversion, and that Brønsted acid sites are essential for the selective formation of N2.
Highly efficient and selective transformations of glycerol to valuable chemicals are currently an attractive and challenging target reaction in biorefineries. A bifunctional catalyst consisting of Pt ...nanoparticles (Pt NPs) and layered-Nb2O5 (L-Nb2O5) efficiently catalyzed the one-pot conversion of glycerol to lactic acid (LA) in water under an oxygen atmosphere without the use of any additives such as strong bases. Mechanistic studies revealed that glycerol was initially oxidized to dihydroxyacetone and glyceraldehyde through dehydrogenation on Pt NPs. After the dehydration step catalyzed by acid sites on L-Nb2O5, the dehydrated intermediate pyruvic aldehyde was converted exclusively on Lewis acid sites, rather than a Brønsted acid, to produce LA through the Cannizzaro reaction. These experimental results represent the successful development of a binary catalyst consisting of metal NPs and solid acid, Pt/L-Nb2O5, for one-pot synthesis of LA from glycerol under additive-free conditions.
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•Glycerol conversion to lactic acid by Pt-based catalysts on supports was examined.•Layered-structure-type Nb2O5 was synthesized and applied as a support.•Pt/L-Nb2O5 possessed the highest acid sites and strongest Lewis acid strength.•The Lewis acid on Pt/L-Nb2O5 catalyzed conversion of pyruvic aldehyde to lactic acid.•Pyruvic aldehyde to lactic acid conversion via the Cannizzaro reaction.
Catalytic biomass conversion under moderate reaction conditions is of great significance as a means of developing synthesis routes to replace petroleum products. The present study demonstrates that a ...high glycerol conversion (40.9%) and significant dihydroxyacetone (DHA) selectivity (65.1%) can be obtained at 303 K under 1 atm air in a base-free solution during the oxidation of glycerol over a bimetallic catalyst supported on SBA-15 (Pt–Bi/SBA-15). CO chemisorption data and transmission electron microscopy characterization show that Bi was deposited on both the step and terrace sites of the Pt surface and consequently modified the catalytic activity. Kinetic studies revealed that the addition of Bi significantly altered the reaction route such that DHA was produced rather than glyceraldehyde (GLD) during the initial stage of the process. 13C NMR analysis found that glycerol tended to chelate with Bi atoms via hydroxyl groups (−OH) to modify the stereochemistry of the reactants. Density functional theory calculation confirmed that each of the three hydroxyl groups of glycerol were captured by the bismuth species, and the middle −OH simultaneously interacted with the platinum surface resulting in selective oxidation of glycerol to DHA. Bismuth ions (Bi3+) were also determined to promote the isomerization of GLD to DHA, which improved the DHA selectivity. These experimental and theoretical results together explain the high activity of the Pt–Bi/SBA-15 under moderate conditions.
We report that ruthenium complexes effectively catalyzed the carboxylate-directed addition of aromatic C–H bonds to aldehydes. The reactions of aromatic acids with a variety of aromatic aldehydes ...including unactivated ones proceeded efficiently to give the corresponding isobenzofuranone derivatives in high yields. The combination of ruthenium(II) complexes with tricyclohexylphosphine led to highly nucleophilic aryl–metal species, which enabled versatile 3 + 2 cycloaddition in the absence of a Lewis acid. This paper also demonstrates the application of supported ruthenium catalysts to the title reaction.
This article discusses the transformation of religious and non-religious practices in contemporary Japanese youth culture. The article employs both western analysis of ‘nones’ and Japanese theories ...to explain this transformation. Three concepts characterize (non-)religiousness in Japanese youth culture: ‘practicing belonging’, ‘vicarious spirituality’, and ‘gendered fetishism’. These concepts are first exemplified in a culture surrounding the concept of ‘tulpa’ (created paranormal beings, derived from Tibetan Buddhism) in Japan. Other examples reflecting each of these concepts are presented, along with a discussion of why Japanese youth culture came to manifest such characteristics. In so doing, we will refrain from drawing a rigid line between religious and non-religious settings, acknowledging that what may appear religious to Japanese scholars may not be viewed as such by western scholars. The factors behind the transformation of religiousness in Japan affect not only religious and spiritual but also non-religious or secular settings, resulting in parallel phenomena.
Selective catalytic oxidation of ammonia (NH3-SCO) into N2 and H2O is considered to be a promising technique to eliminate NH3 pollution. Various Ag/MnO2 catalysts were prepared and applied to ...low-temperature (especially <100 °C) NH3-SCO. The Ag/MnO2-X (X indicating the calcination temperature) catalyst had a variable Ag size and structure depending on the calcination temperature from 200 to 500 °C. The Ag/MnO2-400 catalyst showed 10% NH3 conversion at 35 °C, and the temperature was 90 °C for the complete removal of 50 ppm NH3. More importantly, the N2 selectivities of NH3-SCO over Ag/MnO2-400 at the temperatures ranging from 30 to 120 °C were higher than 96%. Turnover frequencies of NH3 oxidation, N2 selectivity, and byproducts depended on the Ag size/structure. Ag/MnO2-400 with Ag particles of 2.4 nm diameter had the highest density of Ag particles over rod-shaped MnO2 during the reaction, which would be favorable for the formation of adsorbed NO and NH2NO intermediates to form N2 and H2O.
Supported palladium‐gold alloy‐catalyzed cross‐coupling of aryl chlorides and hydrosilanes enabled the selective formation of aryl‐silicon bonds. Whereas a monometallic palladium catalyst ...predominantly promoted the hydrodechlorination of aryl chlorides and gold nanoparticles showed no catalytic activity, gold‐rich palladium‐gold alloy nanoparticles efficiently catalyzed the title reaction to give arylsilanes with high selectivity. A wide array of aryl chlorides and hydrosilanes participated in the heterogeneously‐catalyzed reaction to furnish the corresponding arylsilanes in 34–80% yields. A detailed mechanistic investigation revealed that palladium and gold atoms on the surface of alloy nanoparticles independently functioned as active sites for the formation of aryl nucleophiles and silyl electrophiles, respectively, which indicates that palladium and gold atoms on alloy nanoparticles work together to enable the selective formation of aryl‐silicon bonds.
