Reforming platinum/rhodium steam

Giroux et al. and Farrauto et al., from Engelhard, presented a proprietary catalyst formulation for autothermal reforming, whicii was actually composed of a layer of platinum/rhodium steam reforming catalyst covered with a platinum/pallachum partial oxidation catalyst [57,107]. The catalyst was capable of reforming natural gas. 

Other materials have been studied as catalysts for steam methane reforming. Platinum, rhodium, and ruthenium have high catalytic activity for methane reforming. Suzuki et al. [23] studied the RuAfSZ cermet. They observed that ruthenium had a great activity and a high resistance to carbon deposition. Some promising results have been obtained with ruthenium inserted into strontium doped lanthanum chromite [24]. 

Lenz et al. [73] described the development of a 3 kW monolithic steam-supported partial oxidation reactor for jet fuel, which was developed to supply a solid oxide fuel cell (SOFC). The prototype reactor was composed of a ceramic honeycomb monolith (400 cpsi) operated between 950 C at the reactor inlet and 700°C at the reactor outlet [74]. The radial temperature gradient amoimted to 50 K which was attributed to inhomogeneous mixing at the reactor inlet. The feed composition corresponded to S/C ratio of 1.75 and O/C ratio of 1.0 at 50 000 h GHSV. Under these conditions, about 12 vol.% of each carbon monoxide and carbon dioxide were detected in the reformate, while methane was below the detection limit. Later, Lenz et al. [74] described a combination of three monolithic reactors coated with platinum/rhodium catalyst switched in series for jet fuel autothermal reforming. An optimum S/C ratio of 1.5 and an optimum O/C ratio of 0.83 were determined. Under these conditions 78.5% efficiency at 50 000 h GHSV was achieved. The conversion did not exceed 92.5%. In the product of these... 

The amount of wash coat which was deposited in the testing reactors was in the same range, between 14 and 17 mg, for the rhodium, platinum and palladium samples tested. The platinum sample was calcined after impregnation at a lower temperature of 450 °C, all other samples at 800 °C. The reason for this will be explained below. The content of the active noble metal was around 5 wt.%. All noble metal-containing samples were laboratory-made catalysts. A commercial a-alumina-based catalyst containing 14 wt.% Ni was added for comparison, as nickel catalysts are applied in industrial steam reforming [52],... 

Partial oxidation runs at 700-1000 °C, typically on a platinum or rhodium catalyst supported on alumina or other oxides and c) Autothermal Reforming (ATR) which combines steam reforming and partial oxidation reactions to produce a roughly thermo-neutral reaction ... 

The curves reported in Figure 10 show that the conversion of propane by steam reforming occurs on the Pt-Rh/Al203-La203 between 400°C and 600°C. This result means that rhodium is accessible to the reactants and that the Pt-Rh/Al203-La203 catalyst is composed mainly of monometallic platinum and rhodium particles. 

The metal catalysts active for steam reforming of methane are the group VIII metals, usually nickel. Although other group VIII metals are active, they have drawbacks for example, iron rapidly oxidizes, cobalt cannot withstand the partial pressures of steam, and the precious metals (rhodium, ruthenium, platinum, and palladium) are too expensive for commercial operation. Rhodium and ruthenium are ten times more active than nickel, platinum, and palladium. However, the selectivity of platinum and palladium are better than rhodium [1]. The supports for most industrial catalysts are based on ceramic oxides or oxides stabilized by hydraulic cement. The commonly-used ceramic supports include a-alumina, magnesia, calcium-aluminate, or magnesium-alu-minate [4,8]. Supports used for low temperature reforming (< 770 K) are... 

The purpose of our paper is to compare the behaviors of platinum,rhenium, iridium and rhodium under the same coking conditions (Cyclopentane, 400 0. Re and lr were chosen as they are usually added to Pt in reforming bimetallic catalysts. Rh was studied since it is the most active metal in hydrocarbon steam reforming (Refs. 5-7). 

Steam can be considered a cor-eactant of oxidation during rich-phases (lean in O2) [3-5], In oxy-steam conversion of propane, we showed (fig.l) that propane oxidation was catalyzed by platinum (between 200 and 350°C) while rhodium was the key-component in the catalysis of steam reforming (between 350 and 600°C). Ceria was an excellent promotor of steam reactions [3, 6], particularly when this reaction was carried out in the presence of oxygen. Therefore, the steam reforming activity is an excellent indicator of the rhodium surface state since the activity systematically decreases when the metallic rhodium area decreases [7]. On the other hand, oxidation activity is a more complex indicator of platinum surface state because there exists an optimum dispersion [8,9]. 

Extensive studies of CPO reactions were carrried out by Lanny Schmidt et al. [229] [443] using a millisecond fixed-bed reactor. It was possible to produce syngas over a rhodium monolitii at residence times of milliseconds [229]. Platinum was less active than rhodium. It was shown [242] that the reaetions take place in an oxidation zone as combined surface/gas-phase reactions followed by a steam reforming zone with equilibration of the steam reforming and shift reactions. It was also possible to convert liquid hydrocarbons [164], ethanol [434] and biomass [444] in the milliseeond reactor. 

Carbon deposition is a particular problem with dry reforming, especially with nickel-based catalysts [44—46]. Platinum and rhodium based catalysts show greater tolerance to carbon deposition [47,48]. Therefore, in addition to steam, CO2 can also reform the methane, though it also represents a possible source of carbon deposition. Like steam reforming, dry reforming is also a strongly endothermic reaction. In the case of the dry reforming of methane (Eq. (9)). the heat of reaction AH is -t-248 kj mol . ... 

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