For the first time, it was demonstrated that the catalytic properties of semiconductors can be activated using an external electric field only. More particularly, the TiO2 and Fe2O3 were found to ...produce noticeable amounts of carbon monoxide from carbon dioxide – water vapor gas mixture under the electric field with the strength in the 104 V/cm range. The reported process, i.e. the activation of semiconductors using the electric field is more efficient than the utilization of UV–vis radiation in terms of energy efficiency and amount of products formed.
Display omitted
•Catalytic properties of semiconductors was activated using the external electric field only.•Wet CO2 was converted into CO over TiO2 and Fe2O3 in the presence of field in the 104 V/cm range.•The activity of investigated semiconductors depended on both surface and electronical properties.
Herein, we reported the method of synthesis of sodium titanates using metal-ammonia solution and their photocatalytic activity for the gas-phase reduction of carbon dioxide under visible light. The ...results of physicochemical measurements showed that the obtained samples resemble multiphase systems containing Na2Ti4O9, Na4Ti5O12, and Na0.8Ti4O8 of cylindrical forms. They demonstrated perfect adsorption of visible light and improved activity in the investigated process.
Display omitted
•Intercalation of sodium into titanium dioxide was performed using a solution of sodium metal in liquid ammonia.•Multiphase systems containing sodium titanates of different stoichiometry (Na2Ti4O9, Na4Ti5O12, and Na0.8Ti4O8) were formed.•Localization of sodium ions in titanium dioxide depended on its initial concentration in liquid ammonia.•Absorption of visible light and photocatalytic activity of titanium dioxide were greatly improved.
Ethanol steam reforming was studied over Ni supported catalysts. The effects of support (Al
2
O
3
, Al
2
O
3
–ZnO, and Al
2
O
3
–CeO
2
), metal loading, catalyst activation method, and ...steam-to-ethanol molar feed ratio were investigated. The properties of catalysts were studied by N
2
physisorption, TPD-CO
2
, X-ray diffraction, and temperature programmed reduction. After activity tests, the catalysts were analyzed by TOC analysis. The catalytic activity measurements showed that the addition either of ZnO SSor CeO
2
to alumina enhances both ethanol conversion and promotes selectivity towards hydrogen formation. The same effects were observed for catalysts with higher metal loadings. High process temperature and high water-to-ethanol ratio were found to be beneficial for hydrogen production. An extended catalyst stability tests showed no loss of activity over 50 h on reaction stream. The TOC analysis of spent catalysts revealed only insignificant amounts of carbon deposit.
Monometallic copper and bimetallic palladium–copper catalysts supported on ZnO–Al
2
O
3
, CeO
2
–Al
2
O
3
and ZrO
2
–Al
2
O
3
were prepared by conventional impregnation method and tested in the ...methanol synthesis reaction in a gradient less reactor under elevated pressure (3.5 MPa) at 220°C. The physicochemical properties of prepared catalytic systems were studied using BET, TPR-H
2
, TPD-NH
3
, XRD, SEM-EDS and FT-IR techniques. The results of XRD and SEM-EDS measurements showed the formation of Pd–Cu alloy during the activation of bimetallic catalysts. It was found that the formed alloy was responsible for the improved activity and selectivity of catalysts in the studied reaction. Among investigated catalysts, the highest formation rate of methanol was observed with 2%Pd–20%Cu/ZnO–Al
2
O
3
system. Based on the results of FT-IR measurements it can be concluded that hydrogen molecules adsorb dissociatively on the metallic copper surface to form hydrogen atoms, increasing the hydrogen spillover effect on the metal-support interface. In contrast, CO
2
adsorb on the oxygen vacancies of the support to form carbonates, which can further undergo hydrogenation to methanol.
This review describes features of the structure of carbon nanotubes, their principal characteristics, methods of synthesis, and regions of potential application. Most attention has been paid to the ...use of nanotubes in catalysis. Examples are given of the functionalization of nanotubes and also their use as catalysts, catalytic additives, and catalyst supports.
The results are presented from investigations into the effect of oxidative treatment of carbon nanotubes on the physicochemical and catalytic characteristics of gold, ruthenium, and platinum ...catalysts deposited on them. The surface of multiwalled carbon nanotubes was functionalized in an acidified solution of potassium permanganate. The physicochemical characteristics of the carbon nanotubes and deposited catalysts were studied by the following methods: BET (the Brunauer–Emmet–Teller method), TPR-H (temperature-programmed reduction with hydrogen), XPA (x-ray diffraction), Fourier IRS (infrared spectroscopy with Fourier transformation), TGA (thermogravimetric analysis), scanning electron microscopy (SEM), and chemisorptions of CO and H
2
. The catalytic activity was determined in a flow-type quartz reactor in the range of 250-300°C at atmospheric pressure.
Results are given for a study of the catalytic and physicochemical properties of monometallic Cu/CeO
2
-Al
2
O
3
and bimetallic Pd-Cu/CeO
2
-Al
2
O
3
catalysts for the synthesis of methanol from ...hydrogen and carbon dioxide. The catalytic activity was determined in methanol synthesis in a gradientless reactor at 200°C and 3.5 MPa. The physicochemical properties of these catalytic systems were studied by the BET method (Brunauer−Emmett− Teller method), temperature-programmed reduction of hydrogen (TPR-H
2
), temperature-programmed desorption of ammonia (TPD-NH
3
), x-ray diffraction (XRD), and Fourier-transform IR spectroscopy (FTIR). Our results showed high activity for the palladium-promoted catalyst, which is attributed to a synergistic effect between palladium and copper as well as the formation of a PdCu alloy during activation of this bimetallic catalyst in a reducing atmosphere of 5% H
2
95% Ar.
In order to expand the spectral capabilities of the SERS method, Ag–Cu alloy nanoparticle arrays were studied. Arrays of Ag–Cu nanoparticles were formed by vacuum thermal evaporation and condensation ...on an unheated substrate followed by heat treatment at 230 °C. A higher Raman scattering enhancement in the red region of the spectrum when using an array of nanoparticles of the Ag–Cu eutectic system was found. This enhancement is comparable to the one of pure silver particle array in the blue region of the spectrum. Transmission electron microscopy study has shown that the feature of the Ag–Cu array is that many particles are composite: one part consists of copper, and the other part is made up of silver. These parts have a perfect (possibly heteroepitaxial) boundary. It is believed that the localized surface plasmon resonance excited in the copper part by red light can be transmitted without any loss into the silver part, while the one excited in the silver part by blue light, quickly fades out in the copper part, because blue light has a higher frequency than the copper plasma frequency. From the point of view of SERS applications, the use of Ag–Cu particle arrays allows extending the advantage of silver to the red region of the spectrum.
Display omitted
•Maximum amplification of the Raman signal for the array of Ag–Cu particles is observed in the red region of the spectrum.•Many particles in the array are composite: one part is copper the other is silver.•The border between the copper and silver parts is perfect.
Catalytic properties of monometallic Ni and bimetallic Ru–Ni supported on Al
2
O
3
, CaO–Al
2
O
3
, and MgO–Al
2
O
3
have been studied in mixed reforming of methane. Physicochemical properties of the ...catalytic systems have been studied by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscope and temperature-programmed reduction by hydrogen. It has been shown that, of all the studied samples, the highest conversion of methane and carbon dioxide is achieved in the presence of the Ru−Ni/MgO–Al
2
O
3
bimetallic catalyst. Temperature-programmed reduction has confirmed the effect of hydrogen spillower from ruthenium to NiO. The formation of Ru–Ni alloy has also been found.
Monometallic nickel and bimetallic ruthenium–nickel catalysts supported onto aluminum oxide without additives and aluminum oxide modified with MgO and CaO were prepared by an impregnation method. The ...catalysts were tested in the process of the mixed reforming of methane, and their properties were characterized by thermogravimetry, scanning electron microscopy, and X-ray diffractometry. The total organic carbon content of the catalysts was also measured. The promoting effect of ruthenium and structural promoters on the catalytic activity of Ni/Al
2
O
3
was confirmed. The Ru–Ni/MgO–Al
2
O
3
catalyst exhibited the highest stability and activity; this fact can be explained by the increased adsorption of methane on the surface of ruthenium–nickel clusters.
PDF
