Catalyst performance targets

Catalyst performance targets for stationary and portable applications have not been as consolidated and are usually embedded into MEA performance... 

Ohma A, Shinohara K, liyama A, Yoshida T, Daimaru A (2011) Membrane and catalyst performance targets for automotive fuel cells by FCCJ membrane, catalyst, MEA WG. ECS Trans 41(l) 775-784... 

In general, the following steps are used to ensure optimum regeneration and catalyst performance recovery alow temperature first pass to remove low boiling point hydrocarbons and other volatile matter, an initial combustion step to remove a portion of the sulfur and carbon, and a final combustion step to remove the remaining carbon to the target level. 

The highly evolved catalyst 20 combines several features that have proved successful in simpler cases. The ionic sulfonate groups make the substrate sufficiently soluble for the reaction to be run in water. (The four hydrophilic cyclodextrins perform the same service for the catalyst.) The target reaction, the seledive oxidation of the steroid skeleton, goes back to the early days of enzyme models,1711 and the choice of porphyrin and of manganese as the metal cation are based on many years experience. The aryl groups are perfluorinated because an earlier version of the catalyst suffered self-oxidation. 

The screening work demonstrated that with a (cj-hex3P)2PdCl2 catalyst the targeted methyl pivaloylacetate concentrations and desired reactor residence times could be achieved. Unfortunately, the process still would not meet the targeted catalyst performance (TON >5,000 mol MPA/mol Pd) and required further development directed at improving catalyst and reactor productivity. 

But most of the issues involve the catalyst system itself. The catalyst must be active and selective for the fuel of choice, stable, and resistant to poisoning and attrition while subjected to variations in flow, temperature, and pressure." For successful operation at commercial scale, the reforming process must be able to achieve high conversion of the hydrocarbon feedstock at high space velocities, as well as high H2 and CO selectivities. The reforming catalyst has to meet performance targets (see Table 1) as identified by U.S. DOE before it becomes feasible for use in the fuel reformers of transportation fuel cell... 

The performance targets, such as reactivity of the reaction mixture, selectivity, extension of a production campaign or reproducibility, are controlled by quite a number of parameters. The most important parameters are temperature, pressure, catalyst and promoters, poisons and inhibitors, silicon composition and structure, particle size distribution of solids, dust removal from fluidized-bed reactor, homogeneity of fluidized-bed and the purity of chloromethane. 

Scope Rather broad scope and well-known limitations, also for commercially interesting targets. Often inferior catalyst performance (ee, TON, TOF) compared to an optimized homogeneous analogue. 

At the beginning of our investigations, we set the minimal objectives for the catalyst performance which would allow a future industrial application of the process. The following targets had to be reached enantioselectivity >80%, S/C ratio >1500, TOFav >200 per hour. 

The effect of sulphur on catalyst performance has become more critical as lower tailpipe emissions are targeted. The loss of catalyst efficiency caused by sulphur in the fuel has a larger impact at very low emission levels. 

Fuel flexibility of the fuel reforming subsystem was demonstrated using methane, propane, butane, methanol, ethanol, isooctane, and benchmark gasoline. A 1000-hour catalyst and reactor durability test was completed using benchmark gasoline. Warm transient response of less than 5 seconds was achieved for 10 to 90% of full reformer capacity. A three-fold increase in reformer productivity was achieved compared to the previous year, due to improved catalyst performance and more uniform flow within the reactor. Reactor concepts that would meet FreedomCAR s rapid start-up targets were developed. 

On the improved catalyst project, a combination of higher activity catalysts and thinner catalyst layers is required to achieve the aggressive DOE performance targets. 

Time between catalyst and major component replacement performance targets must be reached at the end of the durability period. 

Due to packaging constraints, not even a DOC could be close-coupled to the engine aU catalysts would be located underbody. It was decided to proceed with the DOC -I- SCR -I- DPF configuration in order to meet the NOx performance target to 85+ % conversion on the FTP-75. Even with rapid warm up, the overall system performance presented a huge challenge. A schematic of the final system includes two DOC bricks, DEF injection (DEF — diesel exhaust fluid, a trade name for automotive grade aqueous urea), a twist mixer, two SCR bricks, and a diesel particulate filter (Fig. 21.10). The DOC and SCR substrates were cordierite and the... 

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