The data on the performance in water gas shift reaction of a powder 5 wt% Pt/Ce0.75Zr0.25O2 and a structured 0.33 wt% Pt/Ce0.75Zr0.25O2/θ-Al2O3/FeCrAl catalysts are reported in this work. For the ...powder one the lowest outlet CO concentrations were shown to be 0.5, 0.9 and 1.5 vol% corresponding to the initial ones of 5, 10 and 15 vol%, respectively; the temperature required to reach these values did not exceed 310 °C. The quasi in situ XPS data have shown that doping CeO2 with Zr enhances the reducibility of the oxide allowing Ce3+ formation without any treatment. Additionally, it was found that there are 20–30% of nonmetallic Pt atoms on the surface even after a treatment in CO at 300 °C. For the structured catalyst the downward temperature gradient along the monolith was observed with a dispersion of 50–60 °C. The lowest CO concentrations were observed at the temperatures at the catalyst's back point of 280 °C–3.9 and 4.3 vol% CO in the dry gas for 15,700 and 31,400 cm3·gcat−1·h−1, respectively, for 10 vol% CO in the feed gas.
•The powder and structured catalysts 5 wt% Pt/Ce0.75Zr0.25O2 for water gas shift reaction.•The catalysts show a good performance below 350 °C in reformate-simulating mixtures.•Doping CeO2 with Zr allows Ce3+ on the oxide surface without any treatment.•20–30% of surface Pt atoms are in nonmetallic state even in a reductive atmosphere.
•Preferential CO oxidation (CO PROX).•Nanopowder of unordered solid solution Pt0.5Co0.5 shows high CO PROX performance.•Pt0.5Co0.5 is more active in total CO oxidation than Pt.•DFT calculations of ...the oxidation of CO on Pt13 and Pt12Co clusters.•Higher activity of Pt12Co due to an electronic effect.
CO preferential (PROX) and total (TOX) oxidation were studied over Pt and Pt0.5Co0.5 nanopowders. Pt0.5Co0.5 exhibited much higher CO PROX performance than Pt, being highly active and selective at 0–80 °C. Low-temperature activity in CO oxidation was shown to be the key feature of bimetallic Pt-Co catalysts in comparison with monometallic Pt. Density functional theory calculations of the oxidation of CO on Pt13 and Pt12Co clusters revealed that a better catalytic activity of bimetallic cluster is due to an electronic effect: the calculated atomic charges on platinum atoms change when cobalt is introduced into its composition.
Semi-regular (SR) variables are not a homogeneous class and their variability is often explained due to pulsations and/or binarity. This study focuses on IRAS 19135+3937, an SRd variable with an ...infrared excess indicative of a dusty disc. A time series of high-resolution spectra, UBV photometry as well as a very accurate light curve obtained by the Kepler satellite, allowed us to study the object in unprecedented detail. We discovered it to be a binary with a period of 127 d. The primary has a low surface gravity and an atmosphere depleted in refractory elements. This combination of properties unambiguously places IRAS 19135+3937 in the subclass of post-asymptotic giant branch stars with dusty discs. We show that the light variations in this object cannot be due to pulsations, but are likely caused by the obscuration of the primary by the circumbinary disc during orbital motion. Furthermore, we argue that the double-peaked Fe emission lines provide evidence for the existence of a gaseous circumbinary Keplerian disc inside the dusty disc. A secondary set of absorption lines has been detected near light minimum, which we attribute to the reflected spectrum of the primary on the disc wall, which segregates due to the different Doppler shift. This corroborates the recent finding that reflection in the optical by this type of discs is very efficient. The system also shows a variable H α profile indicating a collimated outflow originating around the companion. IRAS 19135+3937 thus encompasses all the major emergent trends about evolved disc systems, that will eventually help to place these objects in the evolutionary context.
New results of an investigation of NH3BH3 dehydrogenation with supplying a limited quantity of aqueous solution of a catalyst precursor to a solid-state bed of the hydride particles with subsequent ...external heating at 40–90 °C are presented. Measurements of the reaction layer temperature and the amount of the evolved hydrogen have shown that at external heating temperature higher than 85°С there was acceleration of the first stage of the process, the highly exothermic catalytic hydrolysis of a portion of ammonia borane, which resulted in a stronger heating of the reaction layer and the start of NH3BH3 thermolysis. This type of process is referred to as hydrothermolysis. A TEM, ATR FTIR, and XRD investigation has shown that in the reaction medium the metal chlorides become reduced to an amorphous catalytically active phase. During this process, ammonia reacts with chlorides to form NH4Cl. All of this leads to increased rate of hydrogen generation and hydrogen yield. Gravimetric hydrogen capacity of 7.6 wt% and the average rate of H2 evolution of 39 ml·gcomp.−1min−1 have been achieved at molar ratios of NH3BH3/MCl2 = 50 (M = Co, Ni) and H2O/NH3BH3 = 2 and at external heating of 85°С.
•Exothermal catalytic hydrolysis of NH3BH3 is coupled to its thermolysis.•Catalyst formed in situ enhances the hydrolysis step and heat-up of reaction zone.•NH3 reacts with chlorides to form NH4Cl which initiates the thermolysis step.•The H2 yield of this process depends on the temperature and the catalyst content.•H2 storage capacity −7.6 wt% and average H2 generation rate −39 ml·gcomp.−1min−1.
Abstract
This study shows the effect of conditions on methylene blue sorption from aqueous solutions using amorphous silicon dioxide obtained from rice husk by oxidative roasting with and without ...pre-treatment with 0.1 M HCl. Adsorption activity for methylene blue increases with increasing pH, reaching its maximum above the point of zero charge. Thermodynamic parameter values (ΔG298 > 0, ΔH < 0, ΔS > 0) indicate that methylene blue adsorption is exothermic and occurs with an increase in molecular mobility in the adsorption layer. The process is described by the Freundlich and Dubinin-Astakhov equations, which indicates that it is determined by both electrostatic interaction with active centers on the surface and the volumetric filling of micropores.
The influence of the properties of copper ferrite, prepared by the combustion method from glycine-nitrate precursor, on the kinetics of NH3BH3 hydrolysis, thermolysis and hydrothermolysis are ...presented. As-prepared and annealed samples were studied by X-ray diffraction, scanning electron microscopy, differential dissolution, and attenuated total reflection infrared spectroscopy. It has been shown that in the hydrolysis and hydrothermolysis of NH3BH3, the as-prepared combustion product, which mainly consisted of a cubic spinel Cu0.67Fe2.33O4 with Fe2+ higher content, had the highest activity, as compared with oxides of copper and iron and the annealed samples. According to transmission electron microscopy and X-ray diffraction, in the reaction medium copper ferrite is reduced to nanosized Cu0 and Fe0. This allowed the average rate of H2 evolution per 1 g of the composition to be increased from 30 to 76 ml⋅min−1, as compared with non-catalytic process. The high gravimetric hydrogen capacity (7.3 wt%) was observed at 90 °C.
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•CuO, Fe2O3, Fe3O4, and copper ferrite (CF) were studied in NH3BH3 dehydrogenation.•The combustion method provides an active CF with a high content of Fe2+.•The Fe3+/Fe2+ ratio and water influence the spinel reduction by NH3BH3 to Cu0 and Fe0.•A rate of 76 mlH2⋅min−1⋅g−1comp was achieved in hydrothermolysis (HT) over CF at 90 °C.•Copper facilitates the reduction of iron in CF and increase the GHSC in HT to 7.3 wt%.
The data obtained for the first time on the influence of the sequence of metal deposition and the conditions of formation of the Re-containing component on the properties of a series of catalysts 1.9 ...wt % Pt–1.8 wt % Re/Ce0.75Zr0.25O2 in the water gas shift reaction are presented. It is shown that catalysts in which platinum is deposited first have a content of both metals close to the expected level and make it possible to achieve the maximum CO conversion at a lower temperature compared to a monometallic platinum catalyst. Based on the data on CO chemisorption and calculations of the reaction rate per platinum surface area, it is assumed that the role of the Re-containing phase is to a greater degree related to the stabilization of a highly dispersed platinum state, rather than to participation in the catalysis of the reaction.
The study is presented on the influence of the composition of a ceria-zirconia support on the structure and the activity in water-gas shift reaction of platinum catalysts (Pt/Ce
0.75
Zr
0.25
O
2
and ...Pt/Ce
0.4
Zr
0.5
Y
0.05
La
0.05
O
2
). The structure diagnostics of the samples were performed using high-resolution transmission electron microscopy, powder X-ray diffraction, CO chemisorption and X-ray atomic pair distribution function method. It was shown that the catalysts contain highly dispersed platinum particles not exceeding 2 nm in size. Platinum particles supported on Ce
0.75
Zr
0.25
O
2
are smaller due to the higher specific surface area of the support. The catalysts Pt/Ce
0.75
Zr
0.25
O
2
and Pt/Ce
0.4
Zr
0.5
Y
0.05
La
0.05
O
2
proved to have similar efficiency while having the same platinum content. It was assumed that the catalysts supported on Ce
0.4
Zr
0.5
Y
0.05
La
0.05
O
2
demonstrate a slightly higher turnover frequency per platinum surface atom, but it is likely compensated by the difference in the supported metal particle size.
Nickel-containing catalysts Ni/Ce
1–
x
Zr
x
O
2
exhibit good activity in the methanation of carbon oxides. The studies devoted to the synthesis and testing of Ni–Ce–Zr–O mixed oxide catalytic systems ...have been developed in recent years. However, the possibility of preparing solid solutions Ni–Ce–Zr–O is still not clear. In this work, Ni–Ce
1–
x
Zr
x
O
2
catalysts are synthesized using the Pechini method that has a proven effectiveness in the preparation of mixed oxides. Structural features of the samples are studied by a wide range of powder diffraction and transmission electron microscopy methods, as well as by the atomic pair distribution analysis. The obtained results prove the possibility of preparing the fluorite-like Ni–Ce–Zr–O substitutional solid solution. The crystal structure of this solution is distorted due to the differences between characteristic coordinations and the radii of nickel, cerium, and zirconium cations. It is shown that the Ni–Ce–Zr–O solid solution with a “strained” defective crystal structure is not stable and decomposes under reducing conditions of methanation of carbon oxides to form fine metallic nickel particles.
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