Oxy-steam reforming

The relative activity of the Pt and Rh in the oxy-steam reforming is of interest. As shown in fig. 43, over Pt catalysts the two steps, i.e. oxidation and steam reforming, are clearly discernible, while for the Rh a typical light-off type of conversion curve is observed. This is attributed (Barbier and Duprez 1993, 1994) to both the low oxidation activity of the Rh catalyst and the high steam reforming activity which makes the two steps indistinguishable. The effects of CeC>2 are complex, especially... 

Pt(lwt%)Rh(0.2wt%) catalysts supported on AI2O3 and Ce02-Al203, carbon monoxide and propane oxidation by oxygen (direct oxidation), by steam (water gas shift and steam reforming) and by a mixture of oxygen and steam (oxy-WGS and oxy-steam reforming). 

Fig 1 Oxy-steam reforming of propane on PtRh/Ce02-Al203... 

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]. 

Parizotto NV, Zanchet D, Rocha KO, Marques CMP, Bueno JMC (2009) The effect of Pt promotion on the oxi-reduction properties of alumina supported nickel catalysts for oxidative steam-reforming of methane temperature-resolved XAFS analysis. Appl Catal A 366 122-129... 

The most important aspects of these three processes are summarized in Table 7.7. Pre- and post-combustion processes, as well as oxy-fuel combustion power qrcles, all give a significant reduction in thermal efficiency, and both material and operative costs for a power plant based on these processes would be quite high. Concerning the C02-capture, membranes can be applied in all the three processes cited. In principle, both polymeric and inorganic membranes can be used to produce clean fuel from a mixture gas (from coal gasification or steam-reforming processes) (Bredesen et al., 2004). From one side, due to their simplicity, flexibility, ability to maintain... 

The thermal energy required for methane decomposition is less than that for steam reforming of methane, 37.8 versus 63 kJ/mol H2. Theoretically, no CO2 will be produced via methane decomposition. However, in an oxy-methane decomposition process, a small portion of methane is used as fuel to provide thermal energy for the remaining methane decomposition ... 

Schematically, CO2 capture can be achieved following three main strategies (Figure 39.1) [12] (1) oxy-combustion (or oxy-fuel combustion) where the fuel combustion is performed with pure or enriched O2 instead of air, so that a CO2/ H2O mixture is produced (2) pre-combustion, where the carbon from the fuel is removed prior to combustion (decarbonization) either as CO2, as coke, or in other forms, and whereby the primary fuel heating value is transformed into H2 through partial oxidation, steam reforming, or autothermal reforming with subsequent water-gas shift (WGS) reaction and (3) post-combustion, where CO2 recovery is performed at the end of pipe from a wet exhaust flue gas, usually at 10-30% (v/v) CO2 concentration. The target separations to achieve in these processes to make them feasible are O2/N2 for oxy-combustion, CO2/H2 for precombustion, and CO2/N2 for post-combustion CO2 capture.

The overall analysis of results suggested that the behaviour of the Pt-coated foam was dominated by the gas-phase chemistry (characterized by a moderately exothermic oxy-pyrolysis process), while the behaviour of the Rh-coated foam was dominated by the heterogeneous chemistry (characterized by a sequence of highly exothermic oxidation reactions and highly endothermic steam reforming of the hydrocarbons species). The superiority of the Rh catalyst in steam reforming was very evident and confirmed previous results by Beretta and Forzatti. In both... 

---