Steam-hydrocarbon reforming observation

When steam reforming of saturated hydrocarbons was carried out on nickel catalysts at a high steam - carbon ratio (eg >1.5 mol/atom) [1,8], no carbon deposition was observed after several hours of reaction. The same results (on N1/AI2O3) were observed during CO methanation at H2 CO ratios of 1 to 3 [4]... 

Graf et al.108 performed a comparative study of steam reforming of methane, ethane and ethylene on Pt, Rh, and Pd supported on YSZ. They observed that the reactivity and product distribution depends on the type of noble metal loaded. Over Rh/YSZ catalyst, the reactivity decreased in the order C2H6 > CdE > CH4. On the other hand, over Pt/YSZ, methane reacted much faster than the C2 hydrocarbons and the order of reactivity is CH4 > C2H4 > C2H6 (Fig. 2.8). The higher reactivity of Rh... 

Carbon formation and catalyst deactivation have also been observed in the SRE. Approaches similar to those discussed above for the steam reforming of hydrocarbons are also employed to suppress the carbon formation in ethanol reforming as well.1 7... 

In addition, some of the formation of carbon oxides may be due to steam reforming reactions. The amount of hydrogen produced in the reaction was considerably higher over a pre-oxidized surface, while the amount of hydrocarbons was lower (Figures 2 and 5). It could well be that some of these effects are due to steam reforming reactions catalyzed by nickel exposed in the preoxidized surface. These reactions would lead to the effects observed ... 

Carbon formation has been observed to occur both in the partial oxidation/steam reforming catalyst and in the reformate after it exits the catalyst. Analysis of carbon formed in the steam reformer catalyst found that the carbon was mostly carbonaceous carbon with an approximate H/C ratio of 0.2 - thus about 97% carbon. Carbon that formed in the reformate after it exited the catalyst (probably from unconverted hydrocarbons) has been analyzed to contain 30% by weight solidified hydrocarbons. 

Three-Way Conversion (TWC) Catalyst. TWC-1 was evaluated on the same test unit with the catalyst inlet temperature raised to 650°C. The conversion of all three pollutants over a virgin catalyst is shown in Figure 11. The conversions of carbon monoxide and hydrocarbon at nominal A/F ratios much less than stoichiometric must be attributable mostly to steam reforming since the oxygen available was not sufficient to account for the observed conversion levels. This activity was lost... 

By far the most reports deal with the partial reduction of ZnO, used as support, and subsequent formation of Zn-containing intermetallic compovmds. In the case of Pd/ZnO, a catalyst used for the decomposition (83), the partial oxidation (84-89) and the steam reforming of methanol (90-94), the interaction between the supported Pd particles and the partial reduced support can lead to a mixture of ZnPd, ZnsPd2, and ZnPd2. When this catalyst is used for the hydrogenation of unsaturated hydrocarbons, such as butenes, isoprene, or crotonaldehyde, only the formation of ZnPd is observed (95-97). The same holds for reductive treatments of Pd/ZnO at temperatures above 400°C (Fig. 4). The supported catalyst Pd/ZnO is not the usual case, since normally a mixture of intermetallic compovmds and the originally supported transition metal is observed. 

It is widely accepted that steam reforming of higher hydrocarbons requires S/C ratios higher than 2.5 to prevent coke formation. Thus, coke formation might well have been the origin of catalyst deactivation observed by Villegas et cd. [71]. 

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