Wyniki wyszukiwania - BazTech

1

Low temperature-ethanol steam reforming over Ni-based catalysts supported on CeO2

Palma V, Castaldo F, Ruocco C, Ciambelli P, Iaquaniello G

Journal of Power Technologies

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2015

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Vol. 95, nr 1

54--66

EN

Recent research has been focused on methods to produce hydrogen. There is growing interest in the properties of hydrogen as an energy carrier and the prospects look good for hydrogen use in fuel cell applications, especially when production processes involve clean, renewable sources. Although natural gas steam reforming is the most common way to obtain hydrogen, ethanol steam reforming (ESR) may reduce the dependence on fossil fuels and cut harmful emissions. The ESR reaction is promoted at high temperatures, being strongly endothermic, but in some cases it can be performed at low temperatures, using this process as a pre-reforming step before conventional methane steam reforming (MSR). The low temperature range could reduce: the thermal duty, costs and CO formation, making the produced hydrogen capable of being fed into a fuel cell. The performances of Ni-based catalysts for ethanol steam reforming in a low temperature range (LT-ESR) were evaluated. In particular, the activity of bimetallic samples, prepared by impregnation and coprecipitation, was monitored in both diluted and concentrated feed stream conditions. By comparing bimetallic catalysts with monometallic ones prepared at different Pt or Ni loadings, it was possible to identify the most suitable sample. 3%wtPt / 10wt%Ni / CeO2 obtained by impregnation achieved the highest performances in terms of both H2 yield and durability, allowing perfect agreement with thermodynamic data. However, during stability tests, reaction plugging phenomena occurred. By changing the water-to-ethanol molar ratio from 3 to 6, a considerable increase in durability was observed. The investigation of exhaust catalysts through various characterization techniques was helpful for studying in detail possible sintering or deactivation occurrence.

2

Selektywność i stabilność katalizatorów Pd-Te/Al2O3 w reakcji utleniania glukozy w fazie ciekłej

Frajtak M., Witońska I., Karski S.

Przemysł Chemiczny

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2012

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T. 91, nr 2

193-198

PL

Przedstawiono wyniki badań selektywności i stabilności katalizatorów bimetalicznych o składzie 5%Pd-(0,1–8)%Te/Al₂O₃ w reakcji utleniania glukozy w fazie ciekłej w temp. 60°C. Nośnikowe katalizatory bimetaliczne zawierające 5% mas. Pd i do 5% mas. Te wykazują wyższą aktywność i selektywność do kwasu glukonowego w porównaniu z monometalicznym układem 5%Pd/Al₂O₃. Ponadto, katalizatory Pd-Te/Al₂O₃ charakteryzują się wysoką stabilnością w reakcji utleniania glukozy w fazie ciekłej. Badania XRD i ToF-SIMS wykazały obecność związków międzymetalicznych typu PdTe i PdTe₂ w katalizatorach bimetalicznych, które prawdopodobnie wpływają na ich właściwości katalityczne.

EN

Five bimetallic 5%Pd-X%Te/Al₂O₃ (X = 0.1–8% by mass Te) catalysts were prepd. and used for liq.-phase oxidn. of glucose at 60°C. The catalysts contg. up to 5% of Te showed high stability and higher catalytic activity and selectivity to gluconic acid than the monometallic 5%Pd/Al₂O₃ catalyst. The presence of PdTe and PdTe₂ intermetallic compds. in the catalysts studied was evidenced.

3

Układy bimetaliczne Pd-Ag, Pd-Pt, Pd-Au, Pt-Ag i Pt-Au jako katalizatory heterogeniczne reakcji z udziałem wodoru

Matczak P.

Wiadomości Chemiczne

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2008

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[Z] 62, 7-8

683-708

EN

Heterogeneous catalysts play an important role in the manufacture of various chemical substances in large-scale processes, e.g. crude oil processing and organic synthesis [1]. Heterogeneous catalyst most often consists of a transition metal arranged on an oxide support [2]. The transition metal employed is usually one from Group 10 of the Periodic Table (Ni, Pd or Pt). The Group 10 metals are efficient catalysts of reactions with hydrogen. Such reactions occur in the above-mentioned crude oil processing and organic synthesis. In large-scale applications some modifications of the catalyst properties are often necessary to increase the rate of an appropriate stage of catalyzed reaction and to avoid by-products. The change of the catalytic properties can be obtained by incorporating another metal into the catalyst. Heterogeneous catalysts in which the active part contains two metals are called bimetallic catalysts or, more generally, bimetallic systems [3, 4]. Research on bimetallic catalysts was initiated in the 1960s and since then these catalysts have become an object of increasingly in-depth investigations [5]. The aim of this review is to summarize the available knowledge on heterogeneous bimetallic catalysts. The review has been narrowed only to a few combinations of metals, i.e. Pd-Ag, Pd-Pt, Pd-Au, Pt-Ag, and Pt-Au. In the first part of the review some general information on the forms of the bimetallic systems is presented. The term bimetallic system itself is quite broad and includes, among other, the following representatives (Fig. 1): alloys, surface alloys, monometallic monolayer or pseudomorphic overlayers arranged on the surface of the other metal, monometallic nanoparticles and clusters arranged on the surface of the other metal, alloyed nanoparticles and clusters, core/shell nanoparticles and clusters, and heteroaggregates. Recently, the last three of these representatives have been in the centre of interest [5, 6]. They offer properties very different from those characteristic of bulk materials [15]. Later, the methods of synthesis and structural characterization of the bimetallic systems are described. At present, the preparation of the bimetallic catalysts that exhibit an appropriate structure is difficult and expensive. Hence, further progress in this field is still required. Some new methods of preparation [7, 16-41], as well as many experimental [42-45, 48-67] and theoretical papers [69-77] on structural, energetic and electronic properties of the bimetallic systems are reviewed. In the last part of the review the catalytic behaviour of the Pd-Ag, Pd-Pt, Pd-Au, Pt-Ag and Pt-Au systems is discussed in detail. The discussion concentrates on the catalytic reactions with hydrogen, e.g. hydrogenation, dehydrogenation, hydrogenolysis, etc. [106-137]. In such reactions the bimetallic catalysts exhibit higher selectivity than the monometallic ones. They also have better resistance to deactivation. At the very end of this review the theoretical investigations on H2 dissociation and H adsorption on the bimetallic systems have been mentioned [138-155].

4

Oddziaływanie wodoru z powierzchnią katalizatorów bimetalicznych

Bartczak W. M., Stawowska J., Romanowski S.

Przemysł Chemiczny

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2003

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T. 82, nr 8-9

664-670